electrical engineering construction

Ground Loop Basics

2010-02-22T19:48:00.000-08:00

What is ground loop ?
A ground loop occurs when there is more than one ground connection path between two pieces of equipment. The duplicate ground paths form the equivalent of a loop antenna which very efficiently picks up interference currents. Lead resistance transforms these currents into voltage fluctuations. As a consequence of ground-loop induced voltages, the ground reference in the system is no longer a stable potential, so signals ride on the noise. The noise becomes part of the program signal.

Ground loop is a common wiring conditions where a ground current may take more than one path to return to the grounding electrode at the SERVICE PANEL. AC powered computers all connected to each other through the ground wire in common building wiring. Computers may also be connected by data communications cables. Computers are therefore frequently connected to each other through more than one path. When a multi-path connection between computer circuits exists, the resulting arrangement is known as a "ground loop". Whenever a ground loop exists, there is a potential for damage from INTER SYSTEM GROUND NOISE.

A ground loop in the power or video signal occurs when some components in the same system are receiving its power from a different ground than other components, or the ground potential between two pieces of equipment is not identical.

Usually a potential difference in the grounds causes a current to flow in the interconnects. This in turn modulates the input of the circuitry and is treated like any other signal fed through the normal inputs. Here is an example situation where two grounde equipments are interconnected though signal wire ground and the mains grounding wire. In this situation there is 1A current flowing flowing in the wire which causes 0.1V voltage difference between those two equipemt grounding points.

Example of groundloop problem in system interconnection
Because there is voltage difference between the ewuipments, the signal in the interconnection wire sees that difference added to signal. This canbe heard as humming noise on the wire because the AC current cause the voltage difference of those ground potentials to be also AC voltage. This is one reason for this 50 Hz or 60 Hz noise you hear in the audio signal (or see in video signal as annoying horizonal bars).

Another problem is the current flowing in the signal cable grounding wire. This current passes though the cable and through the equipment. Of the way the curren parsses is not weel designed this can cause lots noise to the equipment or other kind of problems (like computer lockups). Lots of designers count on ground being ground and do not optimize their design to eliminate their sensitivity to ground noise. If you are a product desiger remeber to take care that ground loop current does not cause problems in your equipment by designing proper grounding scheme inside the equipment.

Why ground loop is a problem ?
Ground loop is a common problem when connecting multiple audio-visual system components together, there is a good change of making a nasty ground loops. Ground loop problems are one of the most common noise problems in audio systems. Typical indication of the ground loop problem is audible 50 Hz or 60 Hz (depends on mains voltage frequency used in your country) noise in sound. Most common situation where you meet ground loop problems are when your system includes equipment connected to earthed elecric outlet and antenna network or equipments connected to different grounded outlets around the room.

Everything connected to a single mains earth, which is usually connected to all the earth pins in all the power sockets in one room. Then antenna network is also grounded to same grounding point. This would normally be okay, as the grounding is only connected to each other in a star-like fashion from a central earth wire (leading to the real Earth via a grounding cable or metal pipe) earth cables run through your power cables into the equipment.

Once you take into account that some of your equipment is linked with shielded cable you are quite likely to face some problems. Currents could quite possibly run from one piece of equipment, into the earth cable, into another piece of equipment, then back to the first piece via a shielded audio cable. That wire loop can also pick up interference from nearby magnetic fields and radio transmitters.

The result is that the unwanted signal will be amplified until it is audible and clearly undesireable. Even voltage differences lower than 1 mV can cause annoying humming sound on your audio system.

A problem with audible noise coming from your audio system when other electronic components (fridge, water cooler, ect.) could be the result of of a contaminated ground/neutral conductor in your A/C wiring and a ground loop in uour audio system. This can happen when certain type of devices come on. Typically their power supplies are non-linear and throw garbage back onto the neutral and/or ground conductors. Usually line conditioners or UPS devices will not do anything to help solve this problem.

Common Causes for Computer System Problems
Many times when a user thinks that his system is 'bad' or has 'gone bad' the fault is electrical or magnetic in nature. Monitor problems are very often caused by nearby magnetic fields, neutral wire harmonics, or conducted/transmitted electrical noise. Intermittent lockups of computers are very often the caused by a Ground Loop, an electrical phenomena that sometimes manifests itself when a system and it's peripherals are improperly plugged into different electrical circuits. Many don't even know if their wall outlet is properly wired and grounded, an absolute necessity for a computer and peripheral to operate reliably and safely.

Have you ruled out Ground Loops in your computer system ? Ground loops can cause problems to LAN connections if not properly wired. A ground loop caused by RS-232 connection to other computer can cause computer lockups.

When ground loop is not a problem
Ground loop does not cause problems when all of the following thing are true:
* None of the wires in the loop carry any current
* The loop is not exposed to external changing magnetic fields
* There is no radio frequency interference nearby
If there is any current folowing in any wires, there is then some potentital difference which causes current to flow in other wires also which causes problems. The loop will also act as coil and pick current from the changing magnetic fields around it. Wire loop acts also like an antenna picking up radio signals.

What size of ground potential difference problems we are talking about ?
Literature is speaking about Common Mode Noise of 1 to 2 Volt in "well grounded" plants and over 20 Volts in "poorly grounded" plants. Literature is also speaking of the current measured on a main service grounding (in a large building) in terms of Amps.

Where does this current and voltage difference come from ?
Current leakage of condensators between hot and ground and between neutral and ground, in for instance main filters, cause current in ground wires (and ground loops). The leakage current is typically measures in milliamperes (typically less than 1 mA in computer equipments) per equipment. When you sum up maybe hundreds of such equipments you can easyly get amperes.

The capacitance between line and ground of large heaters and motors, for example, can be much larger than the capacitance in filter capacitors. Currents from this source are usually of the order of 1 amp (rather than 0.1 A or 10 A)

Even a very small induced voltage can cause a very large current in a ground conductor loop, because the resistance (and inductance) are very low. These currents can indeed be tens of amps. Current induction can be caused for example by cables carrying high currents and from transformers.

What those grounding currents and voltage differences can do ?
Small voltage differences just cause noise to be added to the signals. This can cause humming noise to audio, interference bars to video signals and transmission errors to computer networks.

Higher currents can cause more serious problems like sparking in connections, damages equipment and burned wiring. My own experience on th field is limited to sparking connectors, heating cables and damaged computer serial port cards. I have read about burned signal cables and smoking computers because of the ground differentials and large currents caused by them. So be warned about this potential problem and do not do any stupid installations.

Geothermal Energy

2009-04-21T02:34:00.000-07:00

The term geothermal comes from the Greek geo, meaning earth, and therine, meaning heat, thus geothermal energy is energy derived from the natural heat of the earth. The earth’s temperature varies widely, and geothermal energy is usable for a wide range of temperatures from room temperature to well over 300°F. For commercial use, a geothermal reservoir capable of providing hydrothermal (hot water and steam) resources is necessary. Geothermal reservoirs are generally classified as being either low temperature (<150°c)>150°C). Generally speaking, the high temperature reservoirs are the ones suitable for, and sought out for, commercial production of electricity. Geothermal reservoirs are found in “geothermal systems,” which are regionally localized geologic settings where the earth’s naturally occurring heat flow is near enough to the earth’s surface to bring steam or hot water, to the surface. Examples of geothermal systems include the Geysers Region in Northern California, the Imperial Valley in Southern California, and the Yellowstone Region in Idaho, Montana, and Wyoming.

Dry Steam Power Plant
Power plants using dry steam systems were the first type of geothermal power generation plants built. They use steam from the geothermal reservoir as it comes from wells and route it directly through turbine/generator units to produce electricity. An example of a dry steam generation operation is at the Geysers Region in northern California.

Flash Steam Power Plant
Flash steam plants are the most common type of geothermal power generation plants in operation today. They use water at temperatures greater than 360°F (182°C) that is pumped under high pressure to the generation equipment at the surface. Upon reaching the generation equipment, the pressure is suddenly reduced, allowing some of the hot water to convert or “flash” into steam. This steam is then used to power the turbine/generator units to produce electricity. The remaining hot water not flashed into steam, and the water condensed from the steam, is generally pumped back into the reservoir. An example of an area using the flash steam operation is the CalEnergy Navy I flash geothermal power plant at the Coso geothermal field.

Binary Cycle Power Plant
Binary cycle geothermal power generation plants differ from dry steam and flash steam systems because the water or steam from the geothermal reservoir never comes in contact with the turbine/generator units. In the binary system, the water from the geothermal reservoir is used to heat another “working fluid,” which is vaporized and used to turn the turbine/generator units. The geothermal water and the “working fluid” are each confined in separate circulating systems or “closed loops” and never come in contact with each other. The advantage of the binary cycle plant is that they can operate with lower temperature waters (225°F to 360°F) by using working fluids that have an even lower boiling point than water. They also produce no air emissions. An example of an area using a binary cycle power generation system is the Mammoth Pacific binary geothermal power plants at the Casa Diablo geothermal field.

Coal Fire Power Plant

2009-04-21T02:30:00.000-07:00

Coal-fired units produce electricity by burning coal in a boiler to heat water to produce steam. The steam, at tremendous pressure, flows into a turbine, which spins a generator to produce electricity. The steam is cooled, condensed back into water, and returned to the boiler to start the process over.

For example, the coal-fired boilers at TVA’s Kingston Fossil Plant near Knoxville, Tennessee, heat water to about 1,000 degrees Fahrenheit (540 degrees Celsius) to create steam. The steam is piped to the turbines at pressures of more than 1,800 pounds per square inch (130 kilograms per square centimeter). The turbines are connected to the generators and spin them at 3600 revolutions per minute to make alternating current electricity at 20,000 volts. River water is pumped through tubes in a condenser to cool and condense the steam coming out of the turbines.

The Kingston plant generates about 10 billion kilowatt-hours a year, or enough electricity to supply 700,000 homes. To meet this demand, Kingston burns about 14,000 tons of coal a day, an amount that would fill 140 railroad cars.

Power Transmission Line

2009-04-21T02:04:00.000-07:00

Classification of transmission lines

Transmission lines are classified as short, medium and long. When the length of the line is less than about 80Km the effect of shunt capacitance and conductance is neglected and the line is designated as a short transmission line. For these lines the operating voltage is less than 20KV.

For medium transmission lines the length of the line is in between 80km - 240km and the operating line voltage wil be in between 21KV-100KV.In this case the shunt capacitance can be assumed to be lumped at the middle of the line or half of the shunt capacitance may be considered to be lumped each end of the line.The two representations of medium length lines are termed as nominal-T and nominal- π respectively.

Lines more than 240Km long and line voltage above 100KV require calculations in terms of distributed parameters.Such lines are known as long transmission lines.This classification on the basis of length is more or less arbitrary and the real criterion is the degree of accuracy required.

Performance of Transmission Lines
The performance of a power system is mainly dependent on the performance of the transmission lines in the system.It is necessary to calculate the voltage,current and power at any point on a transmission line provided the values at one point are known.

The transmission line performance is governed by its four parameters - series resistance and inductance,shunt capacitance and conductance.All these parameters are distributed over the length of the line.The insulation of a line is seldom perfect and leakage currents flow over the surface of insulators especially during bad weather.This leakage is simulated by shunt conductance.The shunt conductance is in parallel with the system capacitance.Generally the leakage currents are small and the shunt conductance is ignored in calculations.
Performance of transmission lines is meant the determination of efficiency and regulation of lines.The efficiency of transmission lines is defined asThe end of the line where load is connected is called the receiving end and where source of supply is connected is called the sending end.

The Regulation of a line is defined as the change in the receiving end voltage, expressed in percent of full load voltage, from no load to full load, keeping the sending end voltage and frequency constant.

uninterruptible power supply (UPS)

2008-10-29T00:13:00.000-07:00

uninterruptible power supply (UPS) is an electronic device that continues to supply electric power to the load for a certain period of time during a loss of utility power or when the line voltage varies outside normal limits. Its typical application is computer backup power.

The generic standard for UPS systems is IEC 62040-3, which defines limits on the amplitude and duration of deviation of the output voltage acceptable for switching power supply (SMPS) loads.

To make a power supply uninterruptible you need to add an energy storing backup battery, an AC-DC charger and an DC-AC inverter. There are three main types of UPS power backup devices: Standby, Line Interactive and Online. All of them use battery backup when the input fails, but under normal conditions they handle the power differently.

Standby UPS includes a transfer switch that switches the load to the
battery / inverter should the primary AC power source fails. The typical transfer time is between 2 ms and 10 ms depending on the amount of time it takes to detect the lost utility voltage and turn on DC-AC inverter. During this time the power to the load is momentarily interrupted. The equipment's power supply should have hold up ("ride through") time larger then UPS transfer time to avoid data loss. For reference, a typical power factor corrected (PFC) SMPS of a personal computer has at least 10 to 20 ms hold-up time.
Since the inverter operates in standby mode and starts up only when input power fails, the SPS has the highest efficiency (95-97%) and reliability. Because it is also the cheapest UPS, it the most common backup type used for PCs. Note, in some older systems the inverter produced square-wave type output rather then sinusoidal, which could cause problems to sensitive equipment.

The Ferroresonant type of Standby UPS has an additional ferroresonant transformer that shapes output voltage and stores some energy for a smoother transfer. Its main drawback is instability when it is loaded by an SMPS with PFC front end. For this reason such systems are no longer commonly used.

Line Interactive UPS under normal condition smoothes and to some degree regulates the input AC voltage by a filter and a tap-changing transformer. The bi-directional inverter/charger is always connected to the output of the UPS and uses a portion of AC power to keep the battery charged. When the input power fails, the transfer switch disconnects AC input and the battery/inverter provides output power. Its typical efficiency is 90-96%. This type is currently the most common design in 0.5-5 kVA power range.

Online UPS always delivers all or at least a portion of the output power through its inverter even under normal line conditions. There are two main types of on-line UPS: double conversion and delta conversion.

Double Conversion Online UPS is continuously processing the whole power through series connected AC-DC rectifier / charger and DC-AC inverter. Although such type provides PFC and better output power quality then the previous types, the double conversion is resulting in reduced efficiency (80-90 % typical).

Delta Conversion Online UPS includes an additional "Delta Converter" that delivers a portion of the input power directly to the load and provides power factor correction. Such partial bypassing the rectifier / inverter stages
during normal operation results in higher efficiency (up to 97%).

Power Inverter DC-AC definition

2008-10-28T23:50:00.000-07:00

Power inverter is a device that converts electrical power from dc form to ac form using electronic circuits. Its typical application is to convert battery voltage into conventional household AC voltage allowing you to use electronic devices when an AC power is not available. There are basically three kinds of dc-ac inverters: square wave, modified sinewave, and pure sine wave. The square wave is the simplest and the least expensive type, but nowadays it is practically not used commercially because of low quality of power. The modified sine wave topologies (which are actually modified square waves) produce square waves with some dead spots between positive and negative half-cycles. They are suitable for many electronic loads and are the most popular low-cost inverters on the consumer market today. Pure sine-wave inverters produce AC voltage with low total harmonic distortion (typically below 3%). They are used when there is a need for clean sine-wave outputs for some sensitive devices such as medical equipment, laser printers, stereos, etc.
Most commercial DC-AC inverters circuits use the same basic concept: a low dc voltage from the input source is first stepped-up to a higher-voltage dc link corresponding to the peak value of the desired ac voltage. A second power stage then generates an ac voltage by using full-bridge or half bridge configuration. Cheap square wave circuits may also use push-pull converter with step-up transformer. Output voltage can be controlled either in square-wave mode or in pulse width-modulated (PWM) mode. In PWM pure sine-wave circuits, the output voltage and frequency are controlled by varying the duty cycle of the high frequency pulses. Chopped voltage then passes through an output LC lowpass filter to produce a clean sinusoidal output.

Electrical Grid Code

2008-09-15T20:58:00.000-07:00

Philippines Grid code
Energy Regulatory COmmision
Download pdf

Grid Code
Department of Energy
Download pdf

Guidelines to Govern The Formartion of the Grid Management Committee
Department of Energy (DOE), Distribution Code.Distributor, Electric Cooperative, Energy Regulatory Commission (ERC)., Grid Code, Grid Management Committee (GMC)., Grid Owner., Large Customer., Large Generator, Market Operator., National Electrification Administration (NEA), Small Generator., Supplier, System Operator.
Download pdf

SA distributrion grid code development
Distribution Network Code (NC) , Distribution System Operating Code (OC),Distribution Metering Code (MC),Distribution Information Exchange Code (IC): first draft still under construction,Distribution Tariff Code (TC): first draft still under construction
View

Governance of Electrical Standards
With question and Answer portion at the free pdf file
Download pdf

Grid Code Compliance - Voltage Aspects
Download pdf

Review Of The Grid Code
Decision and Notice in Relation to Consultation, COntrol Telephony Electrical Standard
Download pdf

DER Grid Interconnection Standard and Codes
Introduction, Activities and Results,National standards for interconnection of DER, Upgrade to the Canadian Electrical Code:,
Download pdf

Mapping of grid faults and grid codes
Events in Electrical Network, Requirements for LVRT Capability in NationalGrid COdes, Fault Analysis, General Conclusion.
Download pdf

Wind Energy and Grid Integration
Evolution of US Grid Code Activities, Summary of Wind Interconnection Best Practices, System Stability Case Study,
Download pdf

Interpreting the National Electrical Code
Beginning Special Applications Wiring
Preview

The Punjab State Electricity Regulatory Commision
General Code, Planning Code, Load Despatch & System Operation Code, Protection Code, Metering Code, Data Registration Code, Appendices
Preview

grounding electricity

2008-07-14T22:38:00.000-07:00

Electrical codes now require that all 120- and 240-volt circuits have a system of grounding. Grounding assures that all metal parts of a circuit that you might come in contact with are connected directly to the earth, maintaining them at zero voltage. This is a preventive measure. During normal operation, a grounding system does nothing; in the event of a malfunction, however, the grounding protects you and your home from electric shock or fire.

To see why grounding is necessary, look at the drawing, which shows a circuit during normal conditions. Now let's take that same circuit and add a metal ceiling fixture. If the hot wire accidentally became dislodged from the fixture terminal and came into contact with the light fixture's metal canopy, which is highly conductive, the fixture would become electrically charged, or "hot." If you were to touch the fixture under those conditions, a current leakage, or "ground fault," could occur in which you would provide the path to ground for the electric current, and you would get a shock.

The same result could occur in any number of places where electricity and conductive materials are together, such as in power tools and appliances with metal housings, in metal housing boxes, and in metal faceplates. In our example, shock could have been prevented if the circuit had had a grounding system. A grounding wire connecting the neutral bus bar in the service entrance panel to the metal housing of the light fixture would provide an auxiliary electrical path to ground. This grounding wire would carry the fault current back to the distribution center, where the fuse or circuit breaker protecting the circuit would open, shutting off all current flow.

In a typical house circuit, the wiring method dictates how grounding is done. When a home is correctly wired with armored cable, metal conduit, or flexible metal conduit, the metal enclosure can itself serve as the grounding path. But most modern construction uses nonmetallic sheathed cable (type NM), so a separate grounding wire must be run with the circuit wires. Running a separate grounding wire isn't as complicated as it may sound because NM cable contains a grounding wire.

In any of these systems, the end result is the same: an auxiliary path for fault current is provided leading to the neutral bus bar in the service entrance panel, which is tied to ground via the grounding electrode conductor.

In the drawing, the bare grounding wire of the NM cable provides the grounding continuity. The final grounding connection to the receptacle is made through a short piece of wire called a jumper that is bonded to the metal box with either a grounding screw or a grounding clip. If a nonmetallic box were used instead, the grounding wire would be connected directly to the receptacle because that kind of box needs no grounding.

The ground fault circuit interrupter (GFCI or GFI) also protects against electric shock. Whenever the amounts of incoming and outgoing current are unequal, indicating current leakage, the GFCI opens the circuit instantly, cutting off the power. GFCIs are built to trip in 1/40th of a second in the event of a ground fault of 0.005 ampere.

There are two types of GFCIs, both shown. The GFCI breaker is installed in the service panel; it monitors the amount of current going to and coming from an entire circuit. A GFCI receptacle monitors the flow of electricity to that receptacle, as well as to all devices installed in the circuit from that point onward (called "downstream").

The electrical code now requires that receptacles in bathrooms, kitchens, garages, and outdoor locations (in other words, any potentially damp location where the risk of shock is greatest) be protected by a GFCI. You can use either type to serve these areas.

Transformer Theory

2008-06-12T01:59:00.000-07:00

High voltage DC, (Direct Current), transmission lines are the most efficient way to deliver electrical power over long distances with a minimum of loss to heat. However, before this electricity can be used, it must be inverted to AC, (Alternating Current), so that it can be transformed to a manageable voltage. Consequently, most distribution lines are AC voltages. Distribution of electrical power is done at a variety of different voltages, and voltage changes within a distribution system are accomplished by the use of transformers. Below is an example of a typical transformer, used in rural and residential areas of the United States.
In the image on the left, the tall insulators on the top of the transformer are the primary voltage terminals, and the smaller terminals on the side of the cylinder, are the secondary voltage connection points. These transformers are usually mounted to telephone poles, and a copper conductor is routed down the pole to a ground rod. This grounding conductor is attached to the center tap, or neutral terminal, and provides the neutral conductor with a reference to earth ground. Fuses are installed in the tap conductors, between the distribution lines and the primary voltage terminals, and a single transformer often serves several homes.
The voltage waveforms for the output of the transformer on the previous page look like this;
Industrial and commercial electrical systems differ from residential in a rather significant way. Three phase power is considerable more complex than single phase, but more efficient in motor applications, and large area uses. The higher voltages of 277/480v distribution systems are more
efficient, but considerably more dangerous, and should only be maintained and modified by trained and qualified electricians. The seemingly odd voltage relationships of 277/480, and 120/208, result from the timing of the individual output waveforms of the three transformers. In a single phase transformer that is center tapped and referenced to earth ground to produce a neutral, the line-to-neutral voltages are 180 degrees out of phase to each other. Therefore, the line-to-line voltage is exactly twice the line-to-neutral value. Since the line-to-neutral voltage waveforms of a three phase system are 120 degrees out of phase, they never cross the 0 voltage line at the same time. When two of the waveforms intersect above and below the 0 voltage line, they are at the exact same potential, and there is no voltage between them.
The B phase to C phase waveform shown in purple is a single phase, 208 volt relationship that exists in the output from the transformer on the previous page. The waveform produced by the relationship between A phase and C phase, is very similar to this one, except that it occurs 120 electrical degrees away. Likewise, the waveform for A phase and B phase makes up the third “leg” of this three phase, 208 volt transformer output.

The common voltages that exist in the majority of large, commercial and industrial buildings in the United States are 277/480v, and 120/208v, (60hrz, or cycles per second). In parts of Canada and some European countries, the common voltage relationship is 220/380v, (50hrz). In each case, the mathematical relationship between voltages is the same; the larger number is 1.73 times the smaller number. This relationship is a math function derived from the fact that the waveforms are 120 electrical degrees apart. In the following diagram, the 120/208 could be replaced with 277/480, or 220/380. The change in frequency from 60hrz to 50hrz, simply changes the time it takes for each cycle of 360 electrical degrees to occur.
At 60hrz, voltage changes direction 120 a second, and at 50hrz, it changes 100 times a second.
This means that the magnetic field around the conductors of these AC circuits is constantly and rapidly changing. The higher the current the stronger the magnetic field. This constant change in magnetic flux consumes power and produces heat in what is called hysteresis loss. When the current and resulting magnetic fields are strong enough, conductors of other systems in close proximity, such as voice and data transfer circuits, can experience induced voltages that can cause errors and electrical noise.
Motors, lighting ballasts, and switching power supplies, (typical to computer equipment), all produce electrical characteristics that can distort the AC waveform. Electrical circuits and devices are always logical, but sometimes they can be unpredictable, and therefore dangerous, even to qualified electricians. The best tools are knowledge and understanding.

Ohm's Law

2008-06-01T23:09:00.000-07:00

For many conductors of electricity, the electric current which will flow through them is directly proportional to the voltage applied to them. When a microscopic view of Ohm's law is taken, it is found to depend upon the fact that the drift velocity of charges through the material is proportional to the electric field in the conductor. The ratio of voltage to current is called the resistance, and if the ratio is constant over a wide range of voltages, the material is said to be an "ohmic" material. If the material can be characterized by such a resistance, then the current can be predicted from the relationship:
The AC analog to Ohm's law is
where Z is the impedance of the circuit and V and I are the rms or effective values of the voltage and current. Associated with the impedance Z is a phase angle, so that even though Z is the also the ratio of the voltage and current peaks, the peaks of voltage and current do not occur at the same time. The phase angle is necessary to characterize the circuit and allow the calculation of the average power used by the circuit.

If an rms voltage of Vrms =380
is applied to an impedance Z = 10 ohms,
then the rms current will be Irms = 38 A.
If the phase is φ = 3 degrees,
then the power factor is cosφ = 0.9986
and the average power is
Pavg = VrmsIrmscosφ = 14420.21 watts.

The illustration is for a case where the inductive reactance is dominant over the capacitive reactance as shown in the phasor diagram.

Default values will be entered for V and Z above is they are left unspecified, but those values can be changed. If the current is changed, then Z will be recalculated. If a phase angle outside the allowed range -90 to +90 is entered, it will be replaced by a default value.

Electric current

2008-06-01T22:54:00.000-07:00

Electric current is the rate of charge flow past a given point in an electric circuit, measured in Coulombs/second which is named Amperes. In most DC electric circuits, it can be assumed that the resistance to current flow is a constant so that the current in the circuit is related to voltage and resistance by Ohm's law. The standard abbreviations for the units are 1 A = 1C/s.

Y-Δ transformation

2008-06-01T22:50:00.000-07:00

The transformation is used to establish equivalence for networks with 3 terminals. Where three elements terminate at a common node and none are sources, the node is eliminated by transforming the impedances. For equivalence, the impedance between any pair of terminals must be the same for both networks. The equations given here are valid for real as well as complex impedances.Equations for the transformation from Δ-load to Y-load 3-phase circuit

The general idea is to compute the impedance Ry at a terminal node of the Y circuit with impedances R', R'' to adjacent nodes in the Δ circuit by

where RΔ are all impedances in the Δ circuit. This yields the specific formulae

Equations for the transformation from Y-load to Δ-load 3-phase circuit

The general idea is to compute an impedance RΔ in the Δ circuit by
where RP = R1R2 + R2R3 + R3R1 is the sum of the products of all pairs of impedances in the Y circuit and Ropposite is the impedance of the node in the Y circuit which is opposite the edge with RΔ. The formulae for the individual edges are thus

Moving Coil Meters

2008-05-30T21:39:00.000-07:00

The design of a voltmeter, ammeter or ohmmeter begins with a current-sensitive element. Though most modern meters have solid state digital readouts, the physics is more readily demonstrated with a moving coil current detector called a galvanometer. Since the modifications of the current sensor are compact, it is practical to have all three functions in a single instrument with multiple ranges of sensitivity. Schematically, a single range "multimeter" might be designed as illustrated.

Electrical Motor Efficiency

2008-05-29T07:02:00.001-07:00

Electrical motor efficiency is the ratio between the shaft output power - and the electrical input power.
Electrical Motor Efficiency when Shaft Output is measured in Watt

If the power output is measured in Watt (W), efficiency can be expressed as:

ηm = Pout / Pin (1)

where

ηm = motor efficiency

Pout = shaft power out (Watt, W)

Pin = electric power in to the motor (Watt, W)

Electrical Motor Efficiency when Shaft Output is measured in Horsepower

If the power out is measured in horsepower (hp), efficiency can be expressed as:

ηm = Pout 746 / Pin (2)

where

Pout = shaft power out (horsepower, hp)

Pin = electric power in to the motor (Watt, W)

Primary and Secondary Resistance Losses

The electrical power lost in the primary rotor and secondary stator winding resistance are also called the copper losses. The copper loss vary with the load in proportion to the current squared and can be expressed as

Pcl = R I2 (3)

where

Pcl = stator winding - copper loss (W)

R = resistance (Ω)

I = current (Amp)

Iron Losses

These losses are the result of magnetic energy dissipated when when the motors magnetic field is applied to the stator core.

Stray Losses

Stray losses are the losses that remains after primary copper and secondary losses, iron losses and mechanical losses. The largest contribution to the stray losses is harmonic energies generated when the motor operates under load. These energies are dissipated as currents in the copper windings, harmonic flux components in the iron parts, leakage in the laminate core.

Mechanical Losses

Mechanical losses includes friction in the motor bearings and the fan for air cooling.

NEMA Design B Electrical Motors

Electrical motors constructed according NEMA Design B must meet the efficiencies below

Power (hp)	Minimum nominal efficiency *
1-4	78.8
5-9	84.0
10-19	85.5
20-49	88.5
50-99	90.2
100-124	91.7
>125	92.4

*NEMA Design B, Single Speed 1200, 1800, 3600 RPM. Open Drip Proof (ODP) or Totally Enclosed Fan Cooled (TEFC) motors 1 hp and larger that operate more than 500 hours per year.

power factor for a three phase electrical motor

2008-05-29T06:41:00.000-07:00

The power factor of an AC electric power system is defined as the ratio of the active (true or real) power to the apparent power.

Active (Real or True) Power is measured in watts (W) and is the power drawn by the electrical resistance of a system that does useful work.
Apparent Power is measured in volt-amperes (VA) and is the voltage on an AC system multiplied by all the current that flows in it. It is the vector sum of the true and the reactive power.

The third component of the AC power flow, the

Reactive Power, is measured in volt-amperes reactive (VAR). Reactive Power is the power stored in and discharged by the inductive motors, transformers or solenoids.

The reactive power required by an inductive load will increase the amount of apparent power - measured in kilovolt amps (kVA) - in the distribution system. Increasing the reactive and apparent power will cause the power factor - PF - to decrease.

Power Factor
It is common to define the Power Factor - PF - as the cosine of the phase angle between voltage and current - or the "cosφ". The power factor defined by IEEE and IEC is the ratio between the applied true power - and the apparent power, and can in general be expressed as:

PF = Wactive / Wapparent (1)

where

PF = power factor
Wactive = active (true or real) power (Watt)
Wapparent = apparent power (VA, volts amps)

A low power factor is the result of inductive loads such as transformers and electric motors. Unlike resistive loads creating heat by consuming kilowatts, inductive loads require a current flow to create magnetic fields to produce the desired work.

Power factor is an important measurement in electrical AC systems because

an overall power factor less than 1 indicates that the electricity supplier need to provide more generating capacity than actually required
the current waveform distortion that contributes to reduced power factor is caused by voltage waveform distortion and overheating in the neutral cables of three-phase systems

International standards such as IEC 61000-3-2 have been established to control current waveform distortion by introducing limits for the amplitude of current harmonics.

Example - Power Factor
A industrial plant draws 200 A at 400 V and the supply transformer and backup UPS is rated 200 A × 400 V = 80 kVA.

If the power factor - PF - of the loads is only 0.7 - only 80 kVA × 0.7 = 56 kVA of real power is consumed by the system. If the power factor was close to 1, the supply system with transformers, cables, switchgear and UPS could have been done considerably smaller.

A low power factor is expensive and inefficient and some utility companies may charge additional fees when the power factor is less than 0.95. A low power factor will reduce the electrical system's distribution capacity by increasing the current flow and causing voltage drops.

Power Factor for a Three-Phase Motor
The total power required by an inductive device as a motor or similar consists of

Active (true or real) power (measured in kilowatts, kW)
Reactive power - the nonworking power caused by the magnetizing current, required to operate the device (measured in kilovars, kVAR)

The power factor for a three-phase electric motor can be expressed as:

PF = Wapplied / [(3)1/2 U I] (2)

where

PF = power factor
Wapplied = power applied (W, watts)
U = voltage (V)
I = current (A, amps)

electric formulas

2008-05-29T06:31:00.001-07:00

Common electrical units used in formulas and equations are:

Volts - The units of electrical potential or motive force. The force is required to send one ampere of current through one ohm of resistance.
Ohms - The units of resistance. One ohm is the resistance offered to the passage of one ampere when impelled by one volt.
Amperes - The units of current. One ampere is the current which one volt can send through a resistance of one ohm.
Watts - The unit of electrical energy or power. One watt is the product of one ampere and one volt. One ampere of current flowing under the force of one volt gives one watt of energy.
Volt Amperes - The product of the volts and amperes as shown by a voltmeter and ammeter. In direct current systems, volt ampere is the same as watts or the energy delivered. In alternating current systems, the volts and amperes may or may not be 100% synchronous. When synchronous, the volt amperes equal the watts on a wattmeter. When not synchronous, volt amperes exceed watts. More about reactive power.
Kilovolt Ampere - One kilovolt ampere - KVA - is equal to 1,000 volt amperes.
Power Factor - is the ratio of watts to volt amperes.

Electric Power Formulas

W = E I (1a)
W = R I2 (1b)
W = E2/ R (1c)

where

W = power (Watts)
E = voltage (Volts)
I = current (Amperes)
R = resistance (Ohms)

Electric Current Formulas

I = E / R (2a)
I = W / E (2b)
I = (W / R)1/2 (2c)

Electric Resistance Formulas

R = E / I (3a)
R = E2/ W (3b)
R = W / I2 (3c)

Electrical Potential Formulas - Ohms Law

Ohms law can be expressed as:

E = R I (4a)
E = W / I (4b)
E = (W R)1/2 (4c)

Example - Ohm's law

A 12 volt battery supplies power to a resistance of 18 ohms.

I = (12 Volts) / (18 ohms)
= 0.67 Ampere

Electrical Motor Formulas
Electrical Motor Efficiency

μ = 746 Php / Winput (5)

where

μ = efficiency
Php = output horsepower (hp)
Winput = input electrical power (Watts)

or alternatively

μ = 746 Php / (1.732 E I PF) (5b)

Electrical Motor - Power

W3-phase = (E I PF 1.732) / 1,000 (6)

where

W3-phase = electrical power 3-phase motor (kW)
PF = power factor electrical motor

Electrical Motor - Amps

I3-phase = (746 Php) / (1.732 E μ PF) (7)

where

I3-phase = electrical current 3-phase motor (Amps)
PF = power factor electrical motor

2008-05-27T21:51:00.000-07:00

The value of electrical resistance associated with a circuit element or appliance can be determined by measuring the voltage across it with a voltmeter and the current through it with an ammeter and then dividing the measured voltage by the current. This is an application of Ohm's law, but this method works even for non-ohmic resistances where the resistance might depend upon the current. At least in those cases it gives you the effective resistance in ohms under that specific combination of voltage and current.

Conductors and Insulators

2008-05-27T19:16:00.000-07:00

Conductors

In a conductor, electric current can flow freely, in an insulator it cannot. Metals such as copper typify conductors, while most non-metallic solids are said to be good insulators, having extremely high resistance to the flow of charge through them. "Conductor" implies that the outer electrons of the atoms are loosely bound and free to move through the material. Most atoms hold on to their electrons tightly and are insulators. In copper, the valence electrons are essentially free and strongly repel each other. Any external influence which moves one of them will cause a repulsion of other electrons which propagates, "domino fashion" through the conductor.

Simply stated, most metals are good electrical conductors, most nonmetals are not. Metals are also generally good heat conductors while nonmetals are not.

Insulators

Most solid materials are classified as insulators because they offer very large resistance to the flow of electric current. Metals are classified as conductors because their outer electrons are not tightly bound, but in most materials even the outermost electrons are so tightly bound that there is essentially zero electron flow through them with ordinary voltages. Some materials are particularly good insulators and can be characterized by their high resistivities:

materials	Resistivity (ohm m)
Glass	10¹²
Mica	9 x 10¹³
Quartz (fused)	5 x 10¹⁶

This is compared to the resistivity of copper:

materials	Resistivity (ohm m)
Copper	1.7 x 10^-8

Current Law

2008-05-27T18:31:00.000-07:00

The electric current in amperes which flows into any junction in an electric circuit is equal to the current which flows out. This can be seen to be just a statement of conservation of charge. Since you do not lose any charge during the flow process around the circuit, the total current in any cross-section of the circuit is the same. Along with the voltage law, this law is a powerful tool for the analysis of electric circuits.
The current law is one of the main tools for the analysis of electric circuits, along with Ohm's Law, the voltage law and the power relationship. Applying the current law to the above circuits along with Ohm's law and the rules for combining resistors gives the numbers shown below. The determining of the voltages and currents associated with a particular circuit along with the power allows you to completely describe the electrical state of a direct current circuit.

ac three phases

2008-05-25T22:40:00.000-07:00

Three-phase, abbreviated 3φ, refers to three voltages or currents that that differ by a third of a cycle, or 120 electrical degrees, from each other. They go through their maxima in a regular order, called the phase sequence. The three phases could be supplied over six wires, with two wires reserved for the exclusive use of each phase. However, they are generally supplied over only three wires, and the phase or line voltages are the voltages between the three possible pairs of wires. The phase or line currents are the currents in each wire. Voltages and currents are usually expressed as rms or effective values, as in single-phase analysis.

When you connect a load to the three wires, it should be done in such a way that it does not destroy the symmetry. This means that you need three equal loads connected across the three pairs of wires. This looks like an equilateral triangle, or delta, and is called a delta load. Another symmetrical connection would result if you connected one side of each load together, and then the three other ends to the three wires. This looks like a Y, and is called a wye load. These are the only possibilities for a symmetrical load. The center of the Y connection is, in a way, equidistant from each of the three line voltages, and will remain at a constant potential. It is called the neutral, and may be furnished along with the three phase voltages. The benefits of three-phase are realized best for such a symmetrical connection, which is called balanced. If the load is not balanced, the problem is a complicated one one whose solution gives little insight, just numbers. Such problems are best left to computer circuit analysis. Three-phase systems that are roughly balanced (the practical case) can be analyzed profitably by a method called symmetrical components. Here, let us consider only balanced three-phase circuits, which are the most important anyway.

The key to understanding three-phase is to understand the phasor diagram for the voltages or currents. In the diagram at the right, a, b and c represent the three lines, and o represents the neutral. The red phasors are the line or delta voltages, the voltages between the wires. The blue phasors are the wye voltages, the voltages to neutral. They correspond to the two different ways a symmetrical load can be connected. The vectors can be imagined rotating anticlockwise with time with angular velocity ω = 2πf, their projections on the horizontal axis representing the voltages as functions of time. Note how the subscripts on the V's give the points between which the voltage is measured, and the sign of the voltage. Vab is the voltage at point a relative to point b, for example. The same phasor diagram holds for the currents. In this case, the line currents are the blue vectors, and the red vectors are the currents through a delta load. The blue and red vectors differ in phase by 30°, and in magnitude by a factor of √3, as is marked in the diagram.
where Vph is the phase voltage.
In Y(Star) connected system VLine = √3 VPhase , ILine = IPhase .
In Delta connected system VLine = VPhase , ILine = √3 IPhase
The above figure sows the one voltage cycle of a three - phase system .The three colours represent 3 phase voltages displaced by 120 electrical degrees.In the figure Phase 'a' in black , phase 'b' in red ,phase 'c' in blue colour are represented.

transmission lines

2008-05-25T22:34:00.000-07:00

Capacitors

2008-05-25T19:49:00.000-07:00

Capacitance is typified by a parallel plate arrangement and is defined in terms of charge storage:

where

* Q = magnitude of charge stored on each plate.
* V = voltage applied to the plates.

Capacitor Combinations

Capacitors in parallel add ...

If = 50 ,= 20

then

=C1 + C2 = 70

Capacitors in series combine as reciprocals ...

=14.286

Voltage Law

2008-05-25T18:28:00.000-07:00

he voltage changes around any closed loop must sum to zero. No matter what path you take through an electric circuit, if you return to your starting point you must measure the same voltage, constraining the net change around the loop to be zero. Since voltage is electric potential energy per unit charge, the voltage law can be seen to be a consequence of conservation of energy.

The voltage law has great practical utility in the analysis of electric circuits. It is used in conjunction with the current law in many circuit analysis tasks.
The voltage law is one of the main tools for the analysis of electric circuits, along with Ohm's Law, the current law and the power relationship. Applying the voltage law to the above circuits along with Ohm's law and the rules for combining resistors gives the numbers shown below. The determining of the voltages and currents associated with a particular circuit along with the power allows you to completely describe the electrical state of a direct current circuit.

Voltmeter

2008-05-23T21:43:00.000-07:00

A voltmeter measures the change in voltage between two points in an electric circuit and therefore must be connected in parallel with the portion of the circuit on which the measurement is made. By contrast, an ammeter must be connected in series. In analogy with a water circuit, a voltmeter is like a meter designed to measure pressure difference. It is necessary for the voltmeter to have a very high resistance so that it does not have an appreciable affect on the current or voltage associated with the measured circuit. Modern solid-state meters have digital readouts, but the principles of operation can be better appreciated by examining the older moving coil meters based on galvanometer sensors.

Electric Charge

2008-05-23T20:02:00.000-07:00

The unit of electric charge is the Coulomb (abbreviated C). Ordinary matter is made up of atoms which have positively charged nuclei and negatively charged electrons surrounding them. Charge is quantized as a multiple of the electron or proton charge:
The influence of charges is characterized in terms of the forces between them (Coulomb's law) and the electric field and voltage produced by them. One Coulomb of charge is the charge which would flow through a 120 watt lightbulb (120 volts AC) in one second. Two charges of one Coulomb each separated by a meter would repel each other with a force of about a million tons!

The rate of flow of electric charge is called electric current and is measured in Amperes.

In introducing one of the fundamental properties of matter, it is perhaps appropriate to point out that we use simplified sketches and constructs to introduce concepts, and there is inevitably much more to the story. No significance should be attached to the circles representing the proton and electron, in the sense of implying a relative size, or even that they are hard sphere objects, although that's a useful first construct. The most important opening idea, electrically, is that they have a property called "charge" which is the same size, but opposite in polarity for the proton and electron. The proton has 1836 times the mass of the electron, but exactly the same size charge, only positive rather than negative. Even the terms "positive" and "negative" are arbitrary, but well-entrenched historical labels. The essential implication of that is that the proton and electron will strongly attract each other, the historical archtype of the cliche "opposites attract". Two protons or two electrons would strongly repel each other. Once you have established those basic ideas about electricity, "like charges repel and unlike charges attract", then you have the foundation for electricity and can build from there.

From the precise electrical neutrality of bulk matter as well as from detailed microscopic experiments, we know that the proton and electron have the same magnitude of charge. All charges observed in nature are multiples of these fundamental charges. Although the standard model of the proton depicts it as being made up of fractionally charged particles called quarks, those fractional charges are not observed in isolation -- always in combinations which produce +/- the electron charge.

An isolated single charge can be called an "electric monopole". Equal positive and negative charges placed close to each other constitute an electric dipole. Two oppositely directed dipoles close to each other are called an electric quadrupole. You can continue this process to any number of poles, but dipoles and quadrupoles are mentioned here because they find significant application in physical phenomena.

One of the fundamental symmetries of nature is the conservation of electric charge. No known physical process produces a net change in electric charge

Ammeter

2008-05-21T21:46:00.000-07:00

An ammeter is an instrument for measuring the electric current in amperes in a branch of an electric circuit. It must be placed in series with the measured branch, and must have very low resistance to avoid significant alteration of the current it is to measure. By contrast, an voltmeter must be connected in parallel. The analogy with an in-line flowmeter in a water circuit can help visualize why an ammeter must have a low resistance, and why connecting an ammeter in parallel can damage the meter. Modern solid-state meters have digital readouts, but the principles of operation can be better appreciated by examining the older moving coil meters based on galvanometer sensors.

Ohmmeter

2008-05-20T21:48:00.000-07:00

The standard way to measure resistance in ohms is to supply a constant voltage to the resistance and measure the current through it. That current is of course inversely proportional to the resistance according to Ohm's law, so that you have a non-linear scale. The current registered by the current sensing element is proportional to 1/R, so that a large current implies a small resistance. Modern solid-state meters have digital readouts, but the principles of operation can be better appreciated by examining the older moving coil meters based on galvanometer sensors.

Torques in Electrical Motors

2008-05-16T00:32:00.000-07:00

Torque is the turning force through a radius and the units is rated in - N.m - in the SI-system and in - lb.ft - in the imperial system. The torque developed by a synchronous induction motors varies with the speed of the motor when its accelerate from full stop or zero speed, to maximum operating speed.
Locked Rotor or Starting Torque
The Locked Rotor Torque or Starting Torque is the torque the electrical motor develop when its starts at rest or zero speed. A high Starting Torque is more important for application or machines hard to start - as positive displacement pumps, cranes etc. A lower Starting Torque can be accepted in applications as centrifugal fans or pumps where the start load is low or close to zero.

Pull-up Torque
The Pull-up Torque is the minimum torque developed by the electrical motor when it runs from zero to full-load speed (before it reaches the break-down torque point). When the motor starts and begins to accelerate the torque in general decrease until it reach a low point at a certain speed - the pull-up torque - before the torque increases until it reach the highest torque at a higher speed - the break-down torque - point. The pull-up torque may be critical for applications that needs power to go through some temporary barriers achieving the working conditions.

Break-down Torque
The Break-down Torque is the highest torque available before the torque decreases when the machine continues to accelerate to the working conditions.
Full-load Torque or Braking Torque
The Full-load Torque is the torque required to produce the rated power of the electrical motor at full-load speed.
In imperial units the Full-load Torque can be expressed as:

Tfl = Php 5,252 / ωmax (1)
where
Tfl = full-load torque (lb.ft)
Php = horsepower
ωmax = maximum shaft rotational speed (rev/min, rpm)

Example - The Braking Torque
The torque of a 60 hp motor rotating at 1725 rpm can be expressed as:
Tfl = 60 (hp) 5,252 / 1725 (rpm)
= 182.7 lb.ft
NEMA Design
NEMA (National Electrical Manufacturers Association) have classified electrical motors in four different NEMA designs where torques and starting-load inertia are important criterions.
Reduced Voltage Soft Starters
Reduced Voltage Soft Starters are used to limit the starting current and reducing the Locked Rotor Torque or Starting Torque and are common in applications which is hard to start or must be handled with care - as positive displacement pumps, cranes, elevators and similar.

Smoke Detector

2008-05-14T22:56:00.000-07:00

How a Smoke Detector Works

The inner workings of a smoke detector include three main parts: the sensing chamber, a loud horn and a battery (or house voltage power source). A test button lets you know if the battery, sensor and alarm are working properly. Batteries should be replaced yearly, on a regular schedule.

Standard smoke detectors work by ionization; some use a photoelectric cell. With ionization, a tiny amount of radioactive material conducts electricity through the air between two electrodes.

When smoke upsets the current, the alarm sounds. Photoelectric models use a small beam of light. Smoke causes the light to disperse and, when it does, the alarm begins to bleat its warning

Using Smoke Detectors

Most smoke detectors are battery powered but some, particularly those installed during house construction, are wired into a home's electrical system.
Most of the ones that run on line voltage (household current) have a battery backup in case a fire knocks out the house's electrical power.
The main problem with battery-powered smoke detectors is that people don't maintain them. It's estimated that a third of all smoke detectors have missing or dead batteries.
All battery-operated detectors are supposed to signal a low battery; newer models won't close if the battery is removed. New lithium battery models have last up to 10 years; the entire unit is disposable.
Inner workings of a smoke detector include three main parts: the sensing chamber, a loud horn and a battery (or house voltage power source). A test button lets you know if the battery, sensor and alarm are working properly. Batteries should be replaced yearly, on a regular schedule.Smoke detectors should be located on each level of a house and outside each sleeping area (one hallway detector can serve several bedrooms).
Some models sound false alarms when they detect kitchen cooking smoke or high bathroom humidity. It's best not to put them within 20 feet of kitchens, garages, furnaces, hot water heaters, or within 10 feet of a bathroom. Also avoid drafty locations.
A detector should be mounted according to the manufacturer's directions-on the wall or ceiling but not within 4 inches of the corner. The idea is to keep it away from dead air space where smoke might not go.

Galvanometer

2008-05-12T22:17:00.000-07:00

Galvanometer is the historical name given to a moving coil electric current detector. When a current is passed through a coil in a magnetic field, the coil experiences a torque proportional to the current. If the coil's movement is opposed by a coil spring, then the amount of deflection of a needle attached to the coil may be proportional to the current passing through the coil. Such "meter movements" were at the heart of the moving coil meters such as voltmeters and ammeters until they were largely replaced with solid state meters.

The accuracy of moving coil meters is dependent upon having a uniform and constant magnetic field. The illustration shows one configuration of permanent magnet which was widely used in such meter

dc electric power

2008-05-10T04:54:00.000-07:00

The electric power in watts associated with a complete electric circuit or a circuit component represents the rate at which energy is converted from the electrical energy of the moving charges to some other form, e.g., heat, mechanical energy, or energy stored in electric fields or magnetic fields. For a resistor in a D C Circuit the power is given by the product of applied voltage and the electric current:

P = VI

Power = Voltage x Current

The details of the units are as follows:
Power Dissipated in Resistor
Convenient expressions for the power dissipated in a resistor can be obtained by the use of Ohm's Law.
These relationships are valid for AC applications also if the voltages and currents are rms or effective values. The resistor is a special case, and the AC power expression for the general case includes another term called the power factor which accounts for phase differences between the voltage and current.

The fact that the power dissipated in a given resistance depends upon the square of the current dictates that for high power applications you should minimize the current. This is the rationale for transforming up to very high voltages for cross-country electric power distribution.

DC Power in Series and Parallel Circuits
The power relationship is one of the main tools for the analysis of electric circuits, along with Ohm's Law, the voltage law and the current law. Applying the current law to the above circuits along with Ohm's law and the rules for combining resistors gives the numbers shown below. The determining of the voltages and currents associated with a particular circuit along with the power allows you to completely describe the electrical state of a direct current circuit.

Impedance

2008-05-02T02:12:00.000-07:00

While Ohm's Law applies directly to resistors in DC or in AC circuits, the form of the current-voltage relationship in AC circuits in general is modified to the form:
where I and V are the rms or "effective" values. The quantity Z is called impedance. For a pure resistor, Z = R. Because the phase affects the impedance and because the contributions of capacitors and inductors differ in phase from resistive components by 90 degrees, a process like vector addition (phasors) is used to develop expressions for impedance. More general is the complex impedance method.
Impedance Combinations
Combining impedances has similarities to the combining of resistors, but the phase relationships make it practically necessary to use the complex impedance method for carrying out the operations. Combining series impedances is straightforward:
Combining parallel impedances is more difficult and shows the power of the complex impedance approach. The expressions must be rationalized and are lengthy algebraic forms.
Parallel Impedance Expressions
The complex impedance of the parallel circuit takes the form
when rationalized, and the components have the form

Resistance

2008-05-01T23:01:00.000-07:00

The electrical resistance of a circuit component or device is defined as the ratio of the voltage applied to the electric current whichflows through it:

If the resistance is constant over a considerable range of voltage, then Ohm's law, I = V/R, can be used to predict the behavior of the material. Although the definition above involves DC current and voltage, the same definition holds for the AC application of resistors.

Whether or not a material obeys Ohm's law, its resistance can be described in terms of its bulk resistivity. The resistivity, and thus the resistance, is temperature dependent. Over sizable ranges of temperature, this temperature dependence can be predicted from a temperature coefficient of resistance.

Resistivity and Conductivity

The electrical resistance of a wire would be expected to be greater for a longer wire, less for a wire of larger cross sectional area, and would be expected to depend upon the material out of which the wire is made. Experimentally, the dependence upon these properties is a straightforward one for a wide range of conditions, and the resistance of a wire can be expressed as
The factor in the resistance which takes into account the nature of the material is the resistivity . Although it is temperature dependent, it can be used at a given temperature to calculate the resistance of a wire of given geometry.

The inverse of resistivity is called conductivity. There are contexts where the use of conductivity is more convenient.

Electrical conductivity = σ = 1/ρ

Resistor Combinations

The combination rules for any number of resistors in series or parallel can be derived with the use of Ohm's Law, the voltage law, and the current law.
Resistivity Calculation

The electrical resistance of a wire would be expected to be greater for a longer wire, less for a wire of larger cross sectional area, and would be expected to depend upon the material out of which the wire is made (resistivity). Experimentally, the dependence upon these properties is a straightforward one for a wide range of conditions, and the resistance of a wire can be expressed as
Resistance = resistivity x length/area
For a wire of length L = m = ft
and area A = cm2
corresponding to radius r = cm
and diameter inches for common wire gauge comparison
with resistivity = ρ = x 10^ ohm meters
will have resistance R = ohms.

.Electron Volts

2008-04-29T22:23:00.000-07:00

A convenient energy unit, particularly for atomic and nuclear processes, is the energy given to an electron by accelerating it through 1 volt of electric potential difference. The work done on the charge is given by the charge times the voltage difference, which in this case is:

Energies in Electron Volts
Room temperature thermal energy of a molecule..................................0.04 eV

Visible light photons....................................................................................1.5-3.5 eV

Energy for the dissociation of an NaCl molecule into Na+ and Cl- ions:................................................................................................................4.2 eV

Ionization energy of atomic hydrogen ........................................................13.6 eV

Approximate energy of an electron striking a color television screen...............................................................................................................20,000 eV

High energy diagnostic medical x-ray photons...............................200,000 eV (=0.2 MeV)

Typical energies from nuclear decay:
(1) gamma..................................................................................................0-3 MeV
(2) beta.......................................................................................................0-3 MeV
(3) alpha....................................................................................................2-10 MeV

Cosmic ray energies ........................................................................1 MeV - 1000 TeV

Literatur and Free download control system for electric system

2008-04-15T23:56:00.001-07:00

Adaptive Control Systems
Download file

The Control Techniques Drives AND Controls Handbook
Download file
Download file rapidshare

Control in Power Electronics
Portable communication devices and computers would also be impractical. High-performance lighting systems, motor controls, and a wide range of industrial controls depend on power electronics.
Download file rapidshare

Automation And Control Systems Economics
Download file rapidshare
Other file Download

Analysis and Design of Nonlinear Control Systems
Download file rapidshare
Other file Download

introduction to plc controllers
Inside the books: Control panel with a PLC controller, Systematic approach to designing a process control system, PLC controller parts , Power supply, Connecting sensors and output devices, Normally open and Normally closed contacts, Automation a storage door.
Download file rapidshare

High Performance Control
Contents: Performance Enhancement, Book Outline, Stabilizing Controllers, The Stabilizing Controller, All Stabilizing Feedback Controllers,Design Environment, Signals and Disturbances, Off-line Controller Design, Hardware Platform, Control of Hard-disk Drives, Positive Definite Matrices and Matrix Decompositions,
Download file rapidshare

Neural Systems for Control
Book Contents : Neural Networks and Automatic Control, ALearning Sensorimotor Map of Arm Movements: a Step Toward Biological Arm Control, Neuronal Modeling of the Baroreceptor Reflex with Applications in Process Modeling and Control, Identification of Nonlinear Dynamical Systems Using Neural Networks, Neural Network Control of Robot Arms and Nonlinear Systems, Neural Networks for Intelligent Sensors and Control — Practical Issues and Some Solutions, Approximation of Time–Optimal Control for an Industrial Production Plant with General Regression Neural Network
Download file rapidshare

Observers in Control Systems
Contents : Control Systems and the Role of Observers, Control-System Background, Review of the Frequency Domain, 4 The Luenberger Observer: Correcting Sensor Problems, European Symbols for Block Diagrams
Download file rapidshare

Modern Control Technology
Components and System, Introduction to Control System, Introduction to Microprocessor Base Control, Operating Amplifiers and Signal Conditioning, Switches, Relays and Power control Semiconductors, Mechanical System, Sensors, Direct Current Motors, Stepper Motors, Alternating Current Motors, Actuator, Electric Hydraulic and Pneumatic, Feedback Control Principles, Relays Logics, PLCs and Motion Controllers.
Download file rapidshare

Design of Distillation Column Control Systems
Level Control and Feedforward Options, Control of Sidestream Drawoff Columns, Miscellaneous Measurements and Controls, Quantitative Design of Distillation Control Systems
Download file

Modern control engineering
Features an abundance of examples and worked problems throughout the book. Chapter topics include the Laplace transform; mathematical modeling of mechanical systems, electrical systems, fluid systems, and thermal systems; transient and steady-state-response analyses, root-locus analysis and control systems design by the root-locus method
Download file rapidshare

Process Imaging For Automatic Control
This book is the first to treat the entire range of imaging techniques and their use in process control. The authors discuss the basic goals of process modeling and their application to automatic control; direct imaging devices and applications; techniques, hardware, and image reconstruction
Download file rapidshare

Sensitivity of Automatic Control Systems
The book also presents general investigation methods for discontinuous systems, including those described by operator models.Full of powerful new methods and results, this book offers a unique opportunity for those in theoretical investigation and in the design, testing, and exploitation of various control systems to explore the work of Russia's leading researchers in sensitivity theory. Furthermore, its techniques for parametric perturbation investigation, Sensitivity of Control Systems will prove useful in fields outside of control theory,
Download file rapidshare

Literatur and Free download control system for electric system

2008-04-15T23:56:00.000-07:00

Step down transformers

2008-04-05T20:08:00.001-07:00

Step down transformers are designed to reduce electrical voltage. Their primary voltage is greater than their secondary voltage. This kind of transformer "steps down" the voltage applied to it. For instance, a step down transformer is needed to use a 110v product in a country with a 220v supply.

Step down transformers convert electrical voltage from one level or phase configuration usually down to a lower level. They can include features for electrical isolation, power distribution, and control and instrumentation applications. Step down transformers typically rely on the principle of magnetic induction between coils to convert voltage and/or current levels.

Step down transformers are made from two or more coils of insulated wire wound around a core made of iron. When voltage is applied to one coil (frequently called the primary or input) it magnetizes the iron core, which induces a voltage in the other coil, (frequently called the secondary or output). The turns ratio of the two sets of windings determines the amount of voltage transformation.

An example of this would be: 100 turns on the primary and 50 turns on the secondary, a ratio of 2 to 1.

Step down transformers can be considered nothing more than a voltage ratio device.

With step down transformers the voltage ratio between primary and secondary will mirror the "turns ratio" (except for single phase smaller than 1 kva which have compensated secondaries). A practical application of this 2 to 1 turns ratio would be a 480 to 240 voltage step down. Note that if the input were 440 volts then the output would be 220 volts. The ratio between input and output voltage will stay constant. Transformers should not be operated at voltages higher than the nameplate rating, but may be operated at lower voltages than rated. Because of this it is possible to do some non-standard applications using standard transformers.

Single phase step down transformers 1 kva and larger may also be reverse connected to step-down or step-up voltages. (Note: single phase step up or step down transformers sized less than 1 KVA should not be reverse connected because the secondary windings have additional turns to overcome a voltage drop when the load is applied. If reverse connected, the output voltage will be less than desired.)

sourge : www.electricityforum.com

dry type transformers

2008-04-05T20:05:00.001-07:00

Dry type transformers require minimum maintenance to provide many years of reliable trouble free service. Unlike liquid fill transformers which are cooled with oil or fire resistant liquid dielectric, dry type units utilize only environmentally safe, CSA and UL recognized high temperature insulation systems. Dry type transformers provide a safe and reliable power source which does not require fire proof vaults, catch basins or the venting of toxic gasses. These important safety factors allow the installation of dry type transformers inside buildings close to the load, which improves overall system regulation and reduces costly secondary line losses.

Dry type transformers are a rather mature product and technology but, of all the components in a power system, a transformer replacement can be a physically challenging event, extended delivery of a replacement or repair unit and expensive transportation costs. These are transformers whose core and coils are not immersed in an insulating oil.

Fire-resistant dry type or "cast resin" transformers are well suited for installation in high-rise buildings, hospitals, underground tunnels, school, steel factories, chemical plants and places where fire safety is a great concern. Hazard free to the environment, dry type transformers have over the years proven to be highly reliable.

“Dry type” simply means it is cooled by normal air ventilation. The dry type transformer does not require a liquid such as oil or silicone or any other liquid to cool the electrical core and coils.

Dry type transformers are voltage changing (Step-up or Step-down) or isolation device that is air cooled rather than liquid cooled. The transformer case is ventilated to allow air to flow and cool the coil (coils).

sourge : www.electricityforum.com

hight voltage transformer

2008-04-05T20:01:00.000-07:00

High voltage transformers convert votages from one level or phase configuration to another, usually from higher to lower. They can include features for electrical isolation, power distribution, and control and instrumentation applications. High voltage transformers usually depend on the principle of magnetic induction between coils to convert voltage and/or current levels.

High voltage transformers can be configured as either a single-phase primary configuration or a three-phase configuration. The size and cost of a transformer increases when you move down the listing of primary windings. Single-phase primary configurations include single, dual, quad (2+2), 5-lead, and ladder. A 5-Lead primary requires more copper than a Quad (2+2) primary. A Ladder is the least economical primary configuration. Three-phase transformers are connected in delta or wye configurations. A wye-delta transformer has its primary winding connected in a wye and its secondary winding connected in a delta. A delta-wye transformer has its primary winding connected in delta and its secondary winding connected in a wye. Three phase configuration choices include delta - delta, delta - wye (Y), wye (Y) – wye (Y), wye (Y) – delta, wye (Y) – single-phase, delta – single phase, and international. Primary frequencies of incoming voltage signal to primaries available for power transformers include 50 Hz, 60 Hz, and 400 Hz. 50 Hz is common for European power. 60 Hz is common in North American power. 400 Hz is most widely used in aerospace applications. The maximum primary voltage rating is another important parameter to consider. A transformer should be provided with more than one primary winding if it is to be used for several nominal voltages.

Other important specifications to consider when searching for high voltage transformers include maximum secondary voltage rating, maximum secondary current rating, maximum power rating, and output type. A transformer may provide more than one secondary voltage value. The Rated Power of the transformer is the sum of the VA (Volts x Amps) for all of the secondary windings. Output choices include AC or DC. For Alternating Current waveform output, voltage the values are typically given in RMS values. Consult manufacturer for waveform options. For direct current secondary voltage output, consult manufacturer for type of rectification.

High voltage transformers can be constructed as either a toroidal or laminated transformer. Toroidal transformers typically have copper wire wrapped around a cylindrical core so the magnetic flux, which occurs within the coil, doesn't leak out, the coil efficiency is good, and the magnetic flux has little influence on other components. Laminated transformers contain laminated-steel cores; they are also called E-I transformers. These steel laminations are insulated with a nonconducting material, such as varnish, and then formed into a core that reduce electrical losses. Power transformers can be one of many types. These include autotransformer, control transformer, current transformer, distribution transformer, general-purpose transformer, instrument transformer, isolation transformer, potential (voltage) transformer, power transformer, step-up transformer, and step-down transformer. Mountings available for high voltage transformers include chassis mount, dish or disk mount, enclosure or free standing, h frame, and PCB mount.

sourge : www.electricityforum.com

control transformer

2008-04-05T19:56:00.000-07:00

A control transformer is generally used in an electronic circuit that requires constant voltage or constant current with a low power or volt-amp rating. Various filtering devices, such as capacitors, are used to minimize the variations in the output. This results in a more constant voltage or current.

Designed for industrial applications where electromagnetic devices such as relays and solenoids are used, the control transformer maximizes inrush capability and output voltage regulation when electromagnetic devices are initially energized.

Control transformers incorporate high-quality insulating materials. This insulation is used to electrically insulate turn to turn windings, layer to layer windings, primary to secondary windings and ground. Control transformers are vacuum impregnated with VT polyester resin and oven-cured, which seals the surface and eliminates moisture. Filling the entire unit provides a strong mechanical bond and offers protection from the environment.

For proper control transformer specification, three characteristics of the load circuit must be determined in addition to the minimum voltage required to operate the circuit. These are total steady-state (sealed) VA, total inrush VA, and inrush load power factor.

Total steady-state (sealed) VA is the volt-amperes that the transformer must deliver to the load circuit for an extended period of time — the amount of current required to hold the contact in the circuit.
Total inrush VA is the volt amperes that the transformer must deliver upon initial energization of the control circuit. Energization of electromagnetic devices takes 30…50 milliseconds. During this inrush period, the electromagnetic control devices draw many times normal current — 3…10 times normal is typical.
Inrush load power factor is difficult to determine without detailed vector analysis of all the load components. Such an analysis is generally not feasible. Therefore, a safe assumption is 40% power factor.

sourge : electricity forum.....

current transformer

2008-04-05T19:45:00.000-07:00

Central to all of the AC power transducers is the measurement of current. This is accomplished using a current transformer (CT), a "donut" shaped device through which is threaded the wire whose current is to be measured.

A current transformer is designed to produce either an alternating current or alternating voltage proportional to the current being measured. The CTs used with the Wattnode transducers produce a 333 mV alternating voltage when the rated current is measured (either 30A, or 50A). The OSI power transducers employ CT's that produce 5V output at rated value.

All of the 15 CT's employed in the energy monitoring system are "split core." This allows the CT to be opened, installed, and closed, without disconnecting the circuit to which they are attached.

Current Transformer Theory can be explained this way: Central to all of the AC power transducers is the measurement of current. This is accomplished using a current transformer (CT), a "donut" shaped device through which is threaded the wire whose current is to be measured.

A current transformer is a type of "instrument transformer" that is designed to provide a current in its secondary which is accurately proportional to the current flowing in its primary.

Current transformers are designed to produce either an alternating current or alternating voltage proportional to the current being measured. The current transformers used with the Wattnode transducers produce a 333 mV alternating voltage when the rated current is measured (either 30A, or 50A). The OSI power transducers employ CT's that produce 5V output at rated value.

Current transformers measure power flow and provide electrical inputs to power transformers and instruments. Current transformers produce either an alternating current or alternating voltage that is proportional to the measured current. There are two basic types of current transformers: wound and toroidal. Wound current transformers consist of an integral primary winding that is inserted in series with the conductor that carries the measured current. Toroidal or donut-shaped current transformers do not contain a primary winding. Instead, the wire that carries the current is threaded through a window in the toroidal transformer.

Current transformers have many performance specifications, including primary current, secondary current, insulation voltage, accuracy, and burden. Primary current, the load of the current transformer, is the measured current. Secondary current is the range of current outputs. Insulation voltage represents the maximum insulation that current transformers provide when connected to a power source. Accuracy is the degree of certainty with which the measured current agrees with the ideal value. Burden is the maximum load that devices can support while operating within their accuracy ratings. Typically, burden is expressed in volt-amperes (VA), the product of the voltage applied to a circuit and the current.

There are a variety of applications for current transformers. Some devices are used to measure current in electronics equipment or motors. Others are used in street lighting. Current transformers with small footprints mount on printed circuit boards (PCBs) and are used to sense current overloads, detect ground faults, and isolate current feedback signals. Larger devices are used in many three-phase systems to measure current or voltage. Commercial class current transformers that monitor low-power currents are also available. Some current transformers are weatherproof or are rated for outdoor use. Others meet MIL-SPEC, ANSI C-12, or IEC 1036 standards. Generally, ANSI class devices are intended for power monitoring applications where high accuracy and minimum phase angle are required

grounding power

2008-04-05T01:22:00.000-07:00

Generally speaking, the purpose of grounding is to electrically interconnect conductive objects, such as equipment, in order to minimize voltage differences between them. National Electric Code (NEC) requires that 120-volt AC power distribution in homes and other buildings must be a three-wire system

shows how AC power is typically delivered from the utility company to the load at an outlet. For simplicity, only two of the three main utility connections are shown in the drawing.

One of these incoming utility wires, which is often un-insulated, is the grounded or "neutral" conductor. Note that both neutral (white) and line (black) wires are part of the normal load current circuit shown by the arrows. Code requires that the neutral (white) and safety ground (green) wires of each branch circuit be tied or "bonded" to each other and to an earth ground rod at the service entrance.

Any AC line powered device with exposed conductive parts (that includes signal connectors) can become a shock or electrocution hazard if it develops certain internal defects. Insulation is used in power transformers, switches, motors and other internal parts to keep electricity where it belongs. (figure :A look at how AC power is typically delivered.)However, for various reasons, the insulation can fail - effectively connecting "live" power to exposed metal as shown in above figure. such a defect is called a fault.

For example, if the motor in a washing machine overheated and its insulation failed, the full line voltage could energize the housing of the machine! Anyone who accidentally touched the machine and anything grounded, such as a water faucet, at the same time could be seriously shocked or electrocuted.

Remember: current will always return to its source, whether the path is intentional or accidental. Electrons don't care - they can't read schematic. (figure : Watch out for faults… They can be mighty unpleasant)
TRIP THE BREAKER

To return this fault current directly to its source, many devices have a third wire connecting exposed metal to the safety ground pin of their plugs. The outlet safety ground is routed, either via the green wire or metallic conduit, to the neutral conductor at the main breaker panel.

This low-impedance connection to neutral causes a high fault current to flow, quickly tripping the circuit breaker that removes power from the circuit. To function properly, the safety ground must return to neutral. (Note that the EARTH connection had NOTHING to do with this process!)

LIGHTNING & DIRT
The earth itself is the return path for the current in a stroke of lightning. To protect people and equipment from lightning, we must make a connection to actual soil.

Overhead power lines are frequent targets of lightning. As a result, virtually all electric power distribution lines have one conductor connected to earth ground periodically along its length. Before this was done, power lines effectively guided lightning inside buildings, starting fires and killing people.

The (NEC) code-required earth ground at the service entry panel serves to direct lightning to earth ground before it enters the building. For the same reason, the code requires telephone, CATV, and satellite TV cables to "arrest" lightning before it enters a building.

Because soil has resistance just like any other conductor, earth ground connections are not at zero volts with respect to each other or any other mystical or "absolute" reference point. Code allows the resistance of this earth connection to be as high as 25 O.

Since this is far too high to trip the circuit breaker under fault conditions, an earth ground should never be confused with a safety ground. Safety ground must be connected to neutral at the main service entry panel. If more than one ground rod is used, Code requires that all must be bonded to the main utility power-grounding electrode.

OVERHEAD POWER LINE

2008-04-05T00:45:00.000-07:00

An overhead power line is an electric power transmission line suspended by towers or poles. Since most of the insulation is provided by air, overhead power lines are generally the lowest-cost method of transmission for large quantities of electric power. Towers for support of the lines are made of wood (as-grown or laminated), steel (either lattice structures or tubular poles), concrete, aluminum, and occasionally reinforced plastics. The bare wire conductors on the line are generally made of aluminum (either plain or reinforced with steel or sometimes composite materials), though some copper wires are used in medium-voltage distribution and low-voltage connections to customer premises.

The invention of the strain insulator was a critical factor in allowing higher voltages to be used. At the end of the 19th century, the limited electrical strength of telegraph-style pin insulators limited the voltage to no more than 40,000 volts. Today overhead lines are routinely operated at voltages exceeding 765,000 volts between conductors, with even higher voltages possible in some cases.

Overhead power transmission lines are classified in the electrical power industry by the range of voltages:

Low voltage – less than 1000 volts, used for connection between a residential or small commercial customer and the utility.
Medium Voltage – between 1000 volts (1 kV) and to about 33 kV, used for distribution in urban and rural areas.
High Voltage – between 33 kV and about 230 kV, used for sub-transmission and transmission of bulk quantities of electric power and connection to very large consumers.
Extra High Voltage – over 230 kV, up to about 800 kV, used for long distance, very high power transmission.
Ultra High Voltage – higher than 800 kV.

Lines classified as "low voltage" that contact with energized conductors still present a risk of electrocution. A major goal of overhead power line design is to maintain adequate clearance between energized conductors and the ground so as to prevent dangerous contact with the line.

Electrical Unit

2008-04-01T20:56:00.000-07:00

Ampere - (A)
The ampere is that constant current which, if maintained in two straight parallel conductors of infinite length, of negligible circular cross section, and placed 1 meter apart in vacuum, would produce between these conductors a force equal to 2 x 10-7 Newton per meter of length.

Coulomb - (C)
The standard unit of quantity in electrical measurements. It is the quantity of electricity conveyed in one second by the current produced by an electro-motive force of one volt acting in a circuit having a resistance of one ohm, or the quantity transferred by one ampere in one second.

Farad - (F)

The farad is the standard unit of capacitance. Reduced to base SI units, one farad is the equivalent of one second to the fourth power ampere squared per kilogram per meter squared (s4 A2 kg-1 m-2).

When the voltage across a 1 F capacitor changes at a rate of one volt per second (1 V/s), a current flow of 1 A results. A capacitance of 1 F produces 1 V of potential difference for an electric charge of one coulomb (1 C).

In common electrical and electronic circuits, units of microfarads (μF), where 1 μF = 10-6 F, and picofarads (pF), where 1 pF = 10-12 F, are used.

Ohm - (Ω)
The derived SI unit of electrical resistance; the resistance between two points on a conductor when a constant potential difference of 1 volt between them produces a current of 1 ampere.

Henry - (H)
The Henry is the unit of inductance. Reduced to base SI units, one henry is the equivalent of one kilogram meter squared per second squared per ampere squared (kg m2 s-2 A-2).
Inductance

An inductor is a passive electronic component that stores energy in the form of a magnetic field.

The standard unit of inductance is the henry, abbreviated H. This is a large unit. More common units are the microhenry, abbreviated μH (1 μH =10-6H) and the millihenry, abbreviated mH (1 mH =10-3 H). Occasionally, the nanohenry (nH) is used (1 nH = 10-9 H).

Joule - (J)
The unit of energy work or quantity of heat done when a force of one Newton is applied over a displacement of one meter. One joule is the equivalent of one watt of power radiated or dissipated for one second.

In imperial units, the British thermal unit (Btu) is used to express energy. One Btu is equivalent to approximately 1,055 joules.

Siemens - (S)
The unit of electrical conductance S = A / V

Watt
The watt is used to specify the rate at which electrical energy is dissipated, or the rate at which electromagnetic energy is radiated, absorbed, or dissipated.
The unit of power W or Joule/second

Weber - Wb
The unit of magnetic flux.
The flux that, when linking a circuit of one turn, produces in it an electromotive force (Emf) of 1 volt as it is reduced to zero at a uniform rate in one second.

* 1 Weber is equivalent to 108 Maxwells

Tesla - T
The unit of magnetic flux density. The Tesla is equal to 1 Weber per square meter of circuit area.

Volt
The Volt (V) is the Standard International (SI) unit of electric potential or electromotive force. A potential of one volt appears across a resistance of one ohm when a current of one ampere flows through that resistance. Reduced to SI base units, 1 V = 1 kg times m2 times s-3 times A-1 (kilogram meter squared per second cubed per ampere).

electrical engineering construction Privacy Statement

2008-03-28T22:42:00.000-07:00

What follows is the Privacy Statement for all electrical engineering construction websites (a.k.a. blogs) including all the websites run under the electricalplan.blogspot.com domain. Please read this statement regarding our blogs. If you have questions please ask us via our contact form.

Email Addresses
You may choose to add your email address to our contact list via the forms on our websites. We agree that we will never share you email with any third party and that we will remove your email at your request. We don’t currently send advertising via email, but in the future our email may contain advertisements and we may send dedicated email messages from our advertisers without revealing your email addresses to them. If you have any problem removing your email address please contact us via our contact form.

Ownership of Information
electrical engineering construction is the sole owner of any information collected on our websites.

Comments/Message Boards
Most electrical engineering construction websites contain comment sections (a.k.a. message boards). We do not actively monitor these comments and the information on them is for entertainment purposes only. If we are alerted to something we deem inappropriate in any way, we may delete it at our discretion. We use email validation on most of our message boards in order to reduce “comment spam.” These email addresses will not be shared with any third party.

Cookies
Currently we assign cookies to our readers in order to save their preferences. This data is not shared with any third party. Accessing our websites is not dependent on accepting cookies and all major browsers allow you to disable cookies if you wish.

Third Party Cookies
Many of our advertisers use cookies in order to determine the number of times you have seen an advertisement. This is done to limit the number times you are shown the same advertisement. electrical engineering construction does not have access to this data.

Traffic Reports
Our industry-standard traffic reporting records IP addresses, Internet service provider information, referrer strings, browser types and the date and time pages are loaded. We use this information in the aggregate only to provide traffic statistics to advertisers and to figure out which features and editorials are most popular.

Legal proceedings
We will make every effort to preserve user privacy but electrical engineering construction may need to disclose information when required by law.

Business Transitions
If electrical engineering construction is acquired by or merges with another firm, the assets of our websites, including personal information, will likely be transferred to the new firm.

Links
electrical engineering construction websites frequently link to other websites. We are not responsible for the content or business practices of these websites. When you leave our websites we encourage you to read the destination site’s privacy policy. This privacy statement applies solely to information collected by electrical engineering construction

Notification of Changes
When electrical engineering construction makes changes to this privacy policy we will post those changes here.

Contact Information
If you have any questions regarding our privacy policy, please contact us.

electrical engineering construction
arix.st@gmail.com

search-results

2008-03-11T04:12:00.000-07:00

Low Voltage Circuit Breaker

2008-03-02T22:29:00.000-08:00

Small circuit breakers are either installed directly in equipment, or are arranged in a breaker panel.

The 10 ampere DIN rail mounted thermal-magnetic miniature circuit breaker is the most common style in modern domestic consumer units and commercial electrical distribution boards throughout Europe. The design includes the following components:

Actuator lever - used to manually trip and reset the circuit breaker. Also indicates the status of the circuit breaker (On or Off/tripped). Most breakers are designed so they can still trip even if the lever is held or locked in the on position. This is sometimes referred to as "free trip" or "positive trip" operation.
Actuator mechanism - forces the contacts together or apart.
Contacts - Allow current to flow when touching and break the flow of current when moved apart.
Terminals
Bimetallic strip
Calibration screw - allows the manufacturer to precisely adjust the trip current of the device after assembly.
Solenoid
Arc divider / extinguisher

-- article source :wikipedia---

type of circuit breaker

2008-03-02T22:17:00.000-08:00

Many different classifications of circuit breakers can be made, based on their features such as voltage class, construction type, interrupting type, and structural features.

Low voltage (less than 1000 V AC) types are common in domestic, commercial and industrial application, include:

MCB (Miniature Circuit Breaker)—rated current not more than 100 A. Trip characteristics normally not adjustable. Thermal or thermal-magnetic operation. Breakers illustrated above are in this category.

MCCB (Moulded Case Circuit Breaker)—rated current up to 1000 A. Thermal or thermal-magnetic operation. Trip current may be adjustable in larger ratings.

Low voltage power circuit breakers can be mounted in multi-tiers in LV switchboards.

The characteristics of LV circuit breakers are given by international standards such as IEC 947. These circuit breakers are often installed in draw-out enclosures that allow removal and interchange without dismantling the switchgear.

Large low-voltage molded case and power circuit breakers may have electrical motor operators, allowing them to be tripped (opened) and closed under remote control. These may form part of an automatic tranfer switch system for standby power.

Low-voltage circuit breakers are also made for direct-current (DC) applications, for example DC supplied for subway lines. Special breakers are required for direct current because the arc does not have a natural tendancy to go out on each half cycle as for alternating current. A direct current circuit breaker will have blow-out coils which generate a magnetic field that rapidly stretches the arc when interrupting direct current.

Medium-voltage circuit breakers rated between 1 and 72 kV may be assembled into metal-enclosed switchgear line ups for indoor use, or may be individual components installed outdoors in a substation. Air-break circuit breakers replaced oil-filled units for indoor applications, but are now themselves being replaced by vacuum circuit breakers (up to about 35 kV). Likehigh voltage circuit breakers described below, these are also operated by current sensing protective relays operated through current transformers. The charcteristics of MV breakers are given by international standards such as IEC 62271.

Electric power systems require the breaking of higher currents at higher voltages. High-voltage breakers may be free-standing outdoor equipment or a component of a gas-insulated switchgear line-up. Examples of high-voltage AC circuit breakers are:

Vacuum circuit breaker—With rated current up to 3000 A, these breakers interrupt the current by creating and extinguishing the arc in a vacuum container. These can only be practically applied for voltages up to about 35,000 V, which corresponds roughly to the medium-voltage range of power systems. Vacuum circuit breakers tend to have longer life expectancies between overhaul than do air circuit breakers.

Air circuit breaker—Rated current up to 10,000 A. Trip characteristics are often fully adjustable including configurable trip thresholds and delays. Usually electronically controlled, though some models are microprocessor controlled via an integral electronic trip unit. Often used for main power distribution in large industrial plant, where the breakers are arranged in draw-out enclosures for ease of maintenance.

Circuit Breaker Operation

2008-03-02T21:28:00.000-08:00

The following animation shows how a conventional thermal/magnetic circuit breaker works. Current flowing through the circuit heats the bimetal current sensor, causing it to bend. When the amount of bending exceeds a limit, the armature is released and a spring forces the contacts to open. The load current also flows through a magnetic current sensor (coil) which creates a magnetic field that will trip the armature faster than the bimetal strip can respond when very large currents flow. When the contacts open, an arc will be generated that is dissipated in the arc channel. This opening to the outside prevents pressure buildup inside the breaker's case.
The conventional circuit breaker's performance is limited by:

Slow response time of bi-metal current sensors.
Mechanical tolerances that affect both the thermal and the magnetic trip limits.
Inability to differentiate between arcing and normal start up transients due to large motors or incandescent lamps.
The magnetic trip threshold must be set high to prevent nuisance tripping because:

(a) normal transients require a time delay, not available with magnetic sensing, and
(b) there is a strong interaction between thermal history (bi-metal strip position) and magnetic sensitivity.

----source : http://www.zlan.com/brk_info.htm----

construction and concealed equipment lightning protection

2008-02-28T00:41:00.000-08:00

Concealed equiptment for Residential, Commercial and Industrial

The nationwide trend to new home construction in cities and in suburban and rural areas is one that suggests the Concealed System. Concealed Lightning Protection must be installed during construction. Conductor Cables, grounds, and metal interconnections are inconspicuously coursed as the construction progresses. Air terminals (points) are slender and only 12" tall to blend in with the architecture, and are designed to be inconspicuous. Tree protection may be required when the home is built in natural setting.
Details of Concealed Installation
Concealed Installation - On new construction, conductors are coursed along the studding and rafters during framing, in the same manner as plumbing or electric wiring.
Semi-Concealed Installation - On completed buildings, the conductors are hidden by placement along ridge rolls, behind verge boards, spouting, and in other ways, utilizing special fittings for the purpose. There is no damage to the structure and the system is inconspicuous.
Ornamental Points - Ornate points are available on both concealed and semi-concealed systems. Owners are demanding something different - ornamental, distinctive. Modern day architecture lends itself for wrought iron effect ornaments to enhance the appearance of long, plain, ranch type ridges and flat roofs.
Aluminum and Copper - Either of these metals is acceptable for lightning protection systems, but should never be used together without special connectors. Aluminum parts are made heavier and larger to have the same conductivity as copper. There are precautions to be observed in the use of either metal. We will gladly advise on the most suitable choice for any specific condition

article source : www.lightningrod.com

Lightning and Surge Protectors / UPS Devices

2008-02-28T00:21:00.000-08:00

Surge protectors and UPS units are not suitable lightning protection devices. These appliances provide some degree of protection from voltage spikes from everyday power surges and distant lightning strikes. But when lightning strikes a structure directly or very close to it, lightning protection system or not, all bets are off.

A common surge protector simply cannot have any effect on the violent, catastrophic burst of current from a very close or direct lightning strike. Direct lightning current is simply too big to protect with a little electronic device inside a power strip, or even a hefty UPS unit. If your UPS or surge protector is in the way of the lightning's path, all or part of the lightning will just flash over or through the device - regardless of the amount of capacitors and battery banks involved.

Even 'disconnects', or devices that physically switch off power to a device by activating a set of contacts, will not guarantee protection. A small air gap will not stop a lightning bolt that has already jumped across miles of air. It won't think twice about jumping a few more inches, or even a few more feet, especially if the 'path of least resistance' to ground is across the contacts of the disconnect switch.

Not only that, but not even a full-fledged lightning protection system with rods, cables and grounds will guarantee against damage to electronics and computers. For any system to provide 100% protection, it must divert almost 100% of the lightning current from a direct strike, which is nearly physically impossible: Ohm's Law states that for a set of resistances connected in parallel, the current will be distributed across ALL resistances, at levels inversely proportional to the different values of resistance. A house or building is nothing more than a set of resistors 'connected' in parallel- the electrical wiring, plumbing, phone lines, steel framework, etc. (Even though plumbing and electrical wiring, for instance, may not be physically connected, lightning will use side flashes across air gaps to effectively connect them). In a direct lightning strike, the current will not follow only one path- it will distribute itself across all paths to ground depending on each path's resistance.

Lightning current often peaks at 100,000 or more Amperes. With that in mind, consider if you have a lightning protection system installed, and your house is hit directly by lightning. If the protection system takes even 99.9% of the current, then your electrical wiring may take the remaining 0.1%. 0.1% of 100,000 Amperes is a 100 Amp surge through your lines- which may be enough to take out your computer.

It is not uncommon for 'side flashes' to occur inside a house or building, where all or a part of the lightning will jump across an entire room to reach ground- such as from the electrical wiring system to well-grounded water pipes. If your computer is in the way, it'll be time to shop for a new one, even if you have the most expensive protection system installed.

Guarantees on the packaging of UPS/surge protection devices are somewhat misleading when it comes to lightning protection, implying that the devices can stop any effects of a strike. In some cases, they will - as long as they aren't in or near the direct line of fire. But in reality, nothing can guarantee absolute protection from a direct or very close strike.

All this doesn't mean that you shouldn't use a surge protector, UPS, disconnect, or a full-fledged lightning rod system. Any device will provide some degree of protection from everyday power line spikes and distant lightning strikes. But when lightning hits nearby or directly, all bets are off.

The best, and cheapest, way to protect your stereo, television, computer, or any electronic appliance is to unplug all power, telephone, cable, (modem), and antenna connections during a thunderstorm.

source : wvligtning.com

How a lightning protection system works

2008-02-27T21:59:00.000-08:00

Without a designated path to reach ground, a lightning strike may choose to instead utilize any conductor available inside a house or building. This may include the phone, cable, or electrical lines, the water or gas pipes, or (in the case of a steel-framed building) the structure itself. Lightning usually will follow one or more of these paths to ground, sometimes jumping through the air via a side flash to reach a better-grounded conductor (watch animation above). As a result, lightning presents several hazards to any house or building:

Fire- Fire can start anywhere the exposed lightning channel contacts, penetrates or comes near flammable material (wood, paper, gas pipes, etc) in a building - including structural lumber or insulation inside walls and roofs. When lightning follows electrical wiring, it will often overheat or even vaporize the wires, creating a fire hazard anywhere along affected circuits.
Side flashes - Side flashes can jump across rooms, possibly injuring anyone who happens to be in the way. They can also ignite materials such as a gasoline can in a garage.
Damage to building materials - The explosive shock wave created by a lightning discharge can blow out sections of walls, fragment concrete and plaster, and shatter nearby glass.
Damage to appliances - Televisions, VCRs, microwaves, phones, washers, lamps and just about anything plugged into an affected circuit may be damaged beyond repair. Electronic devices and computers are especially vulnerable.

Adding a protection system doesn't prevent a strike, but gives it a better, safer path to ground. The air terminals, cables and ground rods work together to carry the immense currents away from the structure, preventing fire and most appliance damage.

---article source : http://www.wvlightning.com---

Components of a lightning protection system

2008-02-27T20:15:00.000-08:00

Lightning rods or 'air terminals' are only a small part of a complete lightning protection system. In fact, the rods may play the least important role in a system installation. A lightning protection system is composed of three main components:

Rods or 'Air Terminals' - The small, vertical protrusions designed to act as the 'terminal' for a lightning discharge. Rods can be found in different shapes, sizes and designs. Most are topped with a tall, pointed needle or a smooth, polished sphere. The funtionality of different types of lightning rods, and even the neccessity of rods altogether, are subjects of many scientific debates. Lightning Cable.
Conductor Cables - Heavy cables (right) that carry lightning current from the rods to the ground. Cables are run along the tops and around the edges of roofs, then down one or more corners of a building to the ground rod(s).
Ground Rods - Long, thick, heavy rods buried deep into the earth around a protected structure. The conductor cables are connected to these rods to complete a safe path for a lightning discharge around a structure.

The conductor cables and ground rods are the most important components of a lightning protection system, accomplishing the main objective of diverting lightning current safely past a structure. The 'lightning rods' themselves, that is, the pointy vertically-oriented terminals along the edges of roofs, do not play much of a role in the functionality of the system. A full protection setup, given good cable coverage and good grounding, would still work sufficiently without the air terminals.

Lightning protection facts

Rods and protection system don't attract ligtning, nor do they where lightning will strike.
Rods or protection systems do not and cannot prevent lightning, nor can they 'discharge' thunderstorms.
Lightning protection systems (including placement of rods, cables, and groundings) are custom-designed for individual structures and require complex engineering to function properly. They should only be installed by qualified contractors.
Lightning protection systems do not always prevent damage to electronics or computers. You should still unplug such devices during thunderstorms to ensure sufficient protection

fiber optic cable

2008-02-22T17:26:00.000-08:00

Basic Fiber Optic Cable
Tutorial, Type, Construction, Connector and calculating
http://www.arcelect.com/fibercable.htm

Tutorial Fiber Optic Basics
Introduction, Fiber Optic Basics,Basic Cable Design, General Cable Information, Different Types of Cable,Connectors,A Cross Section of Various Cable Types, Wave Division Multiplexers, FIBER-OPTIC TECHNOLOGY, FIBER-OPTIC APPLICATIONS, FIBER-OPTIC ADVANTAGES AND DISADVANTAGES, FIBER-OPTIC ECONOMICS,
http://www.lascomm.com/tutorials/tut_fobasics.htm

What is Fiber Optics
Fiber benefits, Fiber repeaters, The optical fiber cable in the foreground has the equivalent information-carrying capacity of the copper cable in the background., key points in febers history,
http://www.corningcablesystems.com/web/college/fibertutorial.nsf/introfro?OpenForm

Fiber Optics Sensors
Fiber optic sensors can be classified generally as multimode and singlemode in operation., Singlemode devices, The Extrinsic Fizeau Interferometer,
http://www.cirl.com/sensors.php

Basic Concepts of Fiber Optics
Benefits of fiber optics, Basic fiber optics communication system, transmission windows, fiber optics loses calculations, types of fiber optics, dispersion, analog vs. digital, fiber optics sources, fiber optics detectors, fiber optics system design considerations, fiber optic couplers.
http://cord.org/step_online/st1-8/st1-8frameset2.htm

Optical Fiber Communications
Telecom Windows, fiber amplifiers, laser diodes and light-emitting diodes, silica fibers, fiber amplifiers , erbium-doped fiber amplifiers, dispersion-shifted fibers, System Design,fiber-optic link, Transmission Capacity of Optical Fibers, Key Components for Optical Fiber Communications,
http://www.rp-photonics.com/optical_fiber_communications.html

Fiber 101 selected concepts
Optical fiber concepts, core cladding, inside optical fiber
http://www.corning.com/opticalfiber/discovery_center/fiber101/of.aspx

All about fiber optics with free download
Introduction to Fiber Optics, HDTV Standards & Practices for Digital Broadcasting,Why Digital Fiber Optics?, Fiber Optic Cables and Connectors,Optical Power Meter, Scan Converter Buyer's Guide,
http://www.commspecial.com/education/assets.php?doc=eduguide

Fiber optics formulas
Losses due to lateral misalignment formulas, acceptance angle formulas, losses due to angular misalignment formulas, losses due to longitudinal misalignment formulas, determining the number of modes formulas.
http://www.ofr.com/tech_fiber_formula_1.htm

Fiber optics cables
Type codes, mechanical data, dimensions, weights,
http://www.telecables.gr/pdfs/part_II.pdf

Fiber optics
First a bit history, The advantages of using fibre optics, Fibre construction , What's the difference between single-mode and multi-mode? , Light propagation ,Intermodal Dispersion ,So what about the single-mode fibre?
http://www.datacottage.com/nch/fibre.htm

free electrical engineering ebook

2008-02-21T00:43:00.000-08:00

We have listed up several links to free electrical engineering ebooks sources. These free electrical engineering ebooks are important literature and reference for electrical engineering students and electrical engineering practices. Some free electrical engineering ebooks can be downloaded and others read online.

homepages.which.net

Learning motor speed controller completely here.

nfphampden.com
A report on Transformer Theory

bin95.com
Practical Process Control Training - PID Control Brochure, Demo of the Audio book ...'Japanese Path To Maintenance Excellence', PLC Training Seminar, 90 Electrical & Electronic Formulas, Presentation on Electrical Preventive Maintenance, Power Planner by Fabick Power Systems.

ibiblio.org
A free series of textbooks on the subjects of electricity and electronics

Free tech books
Adaptive Control: Stability, Convergence, and Robustness, Integration and Automation of Manufacturing Systems, Automated Manufacturing Systems with PLCs, The Scientist and Engineer's Guide to Digital Signal Processing, 2nd Edition.

Free Six Sigma Calculation Ebook

2008-02-21T00:29:00.000-08:00

Free Six Sigma Calculation Ebook. -This free ebook is a follow up ebook of the first Six Sigma ebook that I’ve posted two days ago. Now I want to tell you about

The ebook is a demonstrator ebook explaining the essential facts about the process sigma metric and how it is calculated.

formulas

2008-02-20T17:47:00.000-08:00

lIST Below links are all free electrical formulas.

Electrical formulas etc. - metric conversion, electrical formulas, conduit weight, maximum no. of conduit, 600 volt building wire, weights and ampacities, ampacities of a insulated conductors, copper to aluminum, receptacle configuration.

Electrical and mechanical formulas.- ohms law, power - ac circuit, power - dc circuit, mechanical, blower motors, pump motors.

Useful electrical formulas.- to find ampers when horsepower is known, amperes when kilowatts are known, amperes when kilovolt amperes are known, kilowatts, kilo volts amperes, horsepower.

Electrical formulas.- admittance, ammeter shunt, batteries, capacitance, capacitance in parallel, capacitance and series, charge division by parallel capacitances, compensation theorem, complex power, current division by parallel resistances, delta-star transformation, dielectric dissipation factor, direct current machines, efficiency, energy, fault calculation, harmonic resonance, inductance, inductance in parallel, inductance in series, induction machines, impedance, instrument transformer, joule's law, kirchhof's laws, maximum power transfer theorem, millman's theorem, mutual inductance, norton's theorem, ohm's law, per-unit system, power, power factor, power factor correction, reactance, reactive loads, reactors, reciprocity theorem, resistance, resistance in parallel, resistance in series,
resonance, star-delta transformation, superposition theorem, symmetrical components, synchronous machines, temperature rise, thermal short time rating, thevenin's theorem , thievenins and norton equivalence, three phase fault level, three phase power, time constants, transformers, voltage division by series capacitances, voltage division by series resistances, voltmater multiplier, wheatstone bridge.

Free download formulas, equation and help.- unit converter, periodic table of elements, kvar calculator, voltage drop calculator, motor protection calculator, motor calculation, circuit design calculator, conduit fill calculator, 4 function calculator, zonal cavity calculator, arc flash calculator, fault current calculator, lighting system calculator, capacitor kvar calculator, software, residential load calculations, touch potentian 2 wire circuit, conversion formulas, electrical formulas based on 60 hz.

from joel deguito

electricity flourescent lighting, lamp & bulb

2008-02-19T21:58:00.001-08:00

The 100,000watt Incandescent lamp
http://silenceisdefeat.org/~lgtngstk/Sites/Bigbulb/bigbulb.htm

An Electronic Ballast (Inverter) to Power HID Lamps from 12 Volt DC !
How The Circuit Works of An electronics Ballast inveter to power,Building The Circuit , The details on the rest of the parts required for this project are as follows:,This basic circuit is very versatile, not only for operating HID lamps or fluorescents, but a variety of other uses as well, with a few basic adaptations, to be outlined here..
http://members.tripod.com/~wvsp/light1.html

Electronic Ballast for Fluorescent Lamps
EXPERIMENT Electronic Ballast Electronic Ballast, Electronic Ballast, Energy distribution of an incandescent lamp. About 10% of the energy is converted to light.
http://www.ece.vt.edu/ece3354/labs/ballast.pdf

Incandescent light bulb
The incandescent light bulb or incandescent lamp is a source of artificial light that works by incandescence.
http://en.wikipedia.org/wiki/Incandescent_light_bulb

Halogen Lamp
Is an incandescent lamp wherein a tungsten filament is sealed into a small transparent envelope filled with a halogen gas such as iodine or bromine.
http://en.wikipedia.org/wiki/Halogen_lamp

High Pressure Sodium Lamps
Working With Exotic Materials,this discharge lamp waited on the invention of a material which sodium would not corrode.
http://americanhistory.si.edu/lighting/tech/hps.htm

Halogen Bulb Types
Halogen Cycle, Halogen Diagram,Halogen vs Standard, Bulb Types, Bases
http://www.goodmart.com/facts/light_bulbs/halogen_bulb_types.aspx

Lava Lamp
Is a novelty item typically used for decoration and ambience rather than illumination
http://en.wikipedia.org/wiki/Lava_lamp

LOw-Pressure Mercury Lamps
Is a highly efficient UV light source of short wavelength. Classified as in the same group as fluorescent lamps or germicidal
http://www.crystec.com/senlampe.htm

Metal Halide Lamps
A Life Story - Metal Halide Lamps, Metal Halide lamps however, such as the MSR and MSD lamps used in High End System's
http://www.highend.com/support/training/metalhalide.asp

Neon Lamp
Is a gas discharge lamp containing primarily neon gas at low pressure
http://en.wikipedia.org/wiki/Neon_lamp

The Low Pressure Sodium Lamp
SOX lamps aregenerally employed in streetlighting applications, primarily because they are the most efficient light sources available This means that they deliver more lumens of light for each watt of power than any other type of lamp SOX installations.
http://www.lamptech.co.uk/Documents/SO1%20Introduction.htm

Purpose of Ballast
Incandescent vs. Fluorescent Lamps, Ballast Function, Fluorescent lamps sold in the US today are available in a wide variety of shapes and sizes.
http://www.ee.bgu.ac.il/~instlab/Experiments/05_FlurLamp/Purpose%20of%20a%20Ballast.pdf

The Fluorescent Lighting System
Is a popular and efficient lighting system used worldwide.The Fluorescent Lighting System Overview, Components of the Fluorescent Lighting System,All about Fluorescent Lamps, Troubleshooting Fluorescent Lighting.
http://nemesis.lonestar.org/reference/electricity/fluorescent/index.html

Sulfur Lamp
The light is distributed though light pipe for hundreds of feet, replacing hundreds of conventional fixtures.
http://members.misty.com/don/sulfbulb.html

Metal Halide Lamps
Available in warm white and cool white correlated color temperature, Low thermal output, Double-ended contacts allow for exact fixture alignment, Operate in enclosed fixtures
http://www.goodmart.com/pdfs/HID031.pdf

Single-phase induction motors

2008-02-13T23:44:00.000-08:00

A three phase motor may be run from a single phase power source. However, it will not self-start. It may be hand started in either direction, comming up to speed in a few seconds. It will only develop 2/3 of the 3-f power rating because one winding is not used.

The single coil of a single phase induction motor does not produce a rotating magnetic field, but a pulsating field reaching maximum intensity at 0o and 180o electrically.Another view is that the single coil excited by a single phase current produces two counter rotating magnetic field phasors, coinciding twice per revolution at 0o (figure a) and 180o (figure e). When the phasors rotate to 90o and -90o they cancel in figure b. At 45o and -45o (figure c) they are partially additive along the +x axis and cancel along the y axis. An analogous situation exists in figure d. The sum of these two phasors is a phasor stationary in space, but alternating polarity in time. Thus, no starting torque is developed.
However, if the rotor is rotated forward at a bit less than the synchronous speed, It will develop maximum torque at 10% slip with respect to the forward rotating phasor. Less torque will be developed above or below 10% slip. The rotor will see 200% - 10% slip with respect to the counter rotating magnetic field phasor. Little torque (see torque vs slip curve) other than a double freqency ripple is developed from the counter rotating phasor. Thus, the single phase coil will develop torque, once the rotor is started. If the rotor is started in the reverse direction, it will develop a similar large torque as it nears the speed of the backward rotating phasor.
Single phase induction motors use a copper or aluminum squirrel cage embedded in a cylinder of steel laminations, typical of poly-phase induction motors.

Permanent-split capacitor motor

One way to solve the single phase problem is to build a 2-phase motor, deriving 2-phase power from single phase. This requires a motor with two windings spaced apart 90o electrical, fed with two phases of current displaced 90o in time. This is called a permanent-split capacitor motor as shown side.
This type of motor suffers increased current magnitude and backward time shift as the motor comes up to speed, with torque pulsations at full speed. The solution is to keep the capacitor (impedance) small to minimize losses. The losses are less than for a shaded pole motor. This motor configuration works well up to 1/4 horsepower (200watt), though, usually applied to smaller motors. The direction of the motor is easily reversed by switching the capacitor in series with the other winding. This type of motor can be adapted for use as a servo motor, described elsewhere is this chapter.This type of motor may have coils embedded into the stator as shown above for larger size motors. The smaller sizes may use the less complex to build salient pole design.

Capacitor-start induction motor

A larger capacitor may be used to start a single phase induction motor via the auxiliary winding if it is switched out by a centrifugal switch once the motor is up to speed. Moreover, the auxiliary winding may be many more turns of heavier wire than used in a resistance split-phase motor to mitigate excessive temperature rise. The result is that more starting torque is available for heavy loads like air conditioning compressors. This motor configuration works so well that it is available in multi-horsepower (multi-kilowatt) sizes.

Capacitor-run motor

A variation of the capacitor-start motor is to start the motor with a relatively large capacitor for high starting torque, but leave a smaller value capacitor in place after starting to improve running characteristics while not drawing excessive current. The additional complexity of the capacitor-run motor is justified for larger size motors.
A motor starting capacitor may be a double-anode non-polar electrolytic capacitor which could be two + to + (or - to -) series connected polarized electrolytic capacitors. Such AC rated electrolytic capacitors have such high losses that they can only be used for intermittent duty (1 second on, 60 seconds off) like motor starting. A capacitor for motor running must not be of electrolytic construction, but a lower loss polymer type.

Resistance split-phase motor
If an auxiliary winding of much fewer turns of smaller wire is placed at 90o electrical to the main winding, it can start a single phase induction motor. With lower inductance and higher resistance, the current will experience less phase shift than the main winding. About 30o of phase difference may be obtained. This coil produces a moderate starting torque, which is disconnected by a centrifugal switch at 3/4 of synchronous speed. This simple (no capacitor) arrangement serves well for motors up to 1/3 horsepower (250 watts) driving easily started loads.This motor has more starting torque than a shaded pole motor (next section), but not as much as a two phase motor built from the same parts. The current density in the auxiliary winding is so high during starting that the consequent rapid temperature rise precludes frequent restarting or slow starting loads.

Nola power factor corrrector
Frank Nola of NASA proposed a power factor corrector for improving the efficiency of AC induction motor in the mid 1970's. It is based on the premise that induction motors are inefficient at less than full load. This inefficiency correlates to a low power factor. The less than unity power factor is due to magnetizing current required by the stator. This fixed current is a larger proportion of total motor current as motor load is decreased. At light load, the full magnetizing current is not required. It could be reduced by decreasing the applied voltage, improving the power factor and efficiency. The power factor corrector senses power factor, and decreases motor voltage, thus restoring a higher power factor and decreasing losses.
Since single-phase motors are about 2 to 4 times as inefficient as three-phase motors, there is potential energy savings for 1-f motors. There is no savings for a fully loaded motor since all the stator magnetizing current is required. The voltage cannot be reduced. But there is potential savings from a less than fully loaded motor. A nominal 117 VAC motor is designed to work at as high as 127 VAC, as low as 104 VAC. That means that it is not fully loaded when operated at greater than 104 VAC, for example, a 117 VAC refrigerator. It is safe for the power factor controller to lower the line voltage to 104-110 VAC. The higher the initial line voltage, the greater the potential savings. Of course, if the power company delivers closer to 110 VAC, the motor will operate more efficiently without any add-on device.
Any substantially idle, 25% FLC or less, single phase induction motor is a candidate for a PFC. Though, it needs to operate a large number of hours per year. And the more time it idles, as in a lumber saw, punch press, or conveyor, the greater the possibility of paying for the controller in a few years operation. It should be easier to pay for it by a factor of three as compared to the more efficient 3-f-motor. The cost of a PFC cannot be recovered for a motor operating only a few hours per day.

Summary: Single-phase induction motors

* Single-phase induction motors are not self-starting without an auxiliary stator winding driven by an out of phase current of near 90o. Once started the auxiliary winding is optional.
* The auxiliary winding of a permanent-split capacitor motor has a capacitor in series with it during starting and running.
* A capacitor-start induction motoronly has a capacitor in series with the auxiliary winding during starting.
* A capacitor-run motor typically has a large non-polarized electrolytic capacitor in series with the auxiliary winding for starting, then a smaller non-electrolytic capacitor during running.
* The auxiliary winding of a resistance split-phase motor develops a phase difference versus the main winding during starting by virtue of the difference in resistance.

Calculating power factor

2008-02-10T21:09:00.000-08:00

As was mentioned before, the angle of this "power triangle" graphically indicates the ratio between the amount of dissipated (or consumed) power and the amount of absorbed/returned power. It also happens to be the same angle as that of the circuit's impedance in polar form. When expressed as a fraction, this ratio between true power and apparent power is called the power factor for this circuit. Because true power and apparent power form the adjacent and hypotenuse sides of a right triangle, respectively, the power factor ratio is also equal to the cosine of that phase angle. Using values from the last example circuitIt should be noted that power factor, like all ratio measurements, is a unitless quantity.

For the purely resistive circuit, the power factor is 1 (perfect), because the reactive power equals zero. Here, the power triangle would look like a horizontal line, because the opposite (reactive power) side would have zero length.

For the purely inductive circuit, the power factor is zero, because true power equals zero. Here, the power triangle would look like a vertical line, because the adjacent (true power) side would have zero length.

The same could be said for a purely capacitive circuit. If there are no dissipative (resistive) components in the circuit, then the true power must be equal to zero, making any power in the circuit purely reactive. The power triangle for a purely capacitive circuit would again be a vertical line (pointing down instead of up as it was for the purely inductive circuit).

Power factor can be an important aspect to consider in an AC circuit, because any power factor less than 1 means that the circuit's wiring has to carry more current than what would be necessary with zero reactance in the circuit to deliver the same amount of (true) power to the resistive load. If our last example circuit had been purely resistive, we would have been able to deliver a full 169.256 watts to the load with the same 1.410 amps of current, rather than the mere 119.365 watts that it is presently dissipating with that same current quantity. The poor power factor makes for an inefficient power delivery system.

Poor power factor can be corrected, paradoxically, by adding another load to the circuit drawing an equal and opposite amount of reactive power, to cancel out the effects of the load's inductive reactance. Inductive reactance can only be canceled by capacitive reactance, so we have to add a capacitor in parallel to our example circuit as the additional load. The effect of these two opposing reactances in parallel is to bring the circuit's total impedance equal to its total resistance (to make the impedance phase angle equal, or at least closer, to zero).

Since we know that the (uncorrected) reactive power is 119.998 VAR (inductive), we need to calculate the correct capacitor size to produce the same quantity of (capacitive) reactive power. Since this capacitor will be directly in parallel with the source (of known voltage), we'll use the power formula which starts from voltage and reactance:

Let's use a rounded capacitor value of 22 mF and see what happens to our circuit:

The power factor for the circuit, overall, has been substantially improved. The main current has been decreased from 1.41 amps to 994.7 milliamps, while the power dissipated at the load resistor remains unchanged at 119.365 watts. The power factor is much closer to being 1:

Since the impedance angle is still a positive number, we know that the circuit, overall, is still more inductive than it is capacitive. If our power factor correction efforts had been perfectly on-target, we would have arrived at an impedance angle of exactly zero, or purely resistive. If we had added too large of a capacitor in parallel, we would have ended up with an impedance angle that was negative, indicating that the circuit was more capacitive than inductive.

It should be noted that too much capacitance in an AC circuit will result in a low power factor just as well as too much inductance. You must be careful not to over-correct when adding capacitance to an AC circuit. You must also be very careful to use the proper capacitors for the job (rated adequately for power system voltages and the occasional voltage spike from lightning strikes, for continuous AC service, and capable of handling the expected levels of current).

If a circuit is predominantly inductive, we say that its power factor is lagging (because the current wave for the circuit lags behind the applied voltage wave). Conversely, if a circuit is predominantly capacitive, we say that its power factor is leading. Thus, our example circuit started out with a power factor of 0.705 lagging, and was corrected to a power factor of 0.999 lagging.

REVIEW: Poor power factor in an AC circuit may be ``corrected,'' or re-established at a value close to 1, by adding a parallel reactance opposite the effect of the load's reactance. If the load's reactance is inductive in nature (which is almost always will be), parallel capacitance is what is needed to correct poor power factor

AC commutator motors

2008-01-01T22:49:00.000-08:00

AC commutator motors, like comparable DC motors, have higher starting torque and higher speed than AC induction motors. The series motor operates well above the synchronous speed of a conventional AC motor. AC commutator motors may be either single-phase or poly-phase. The single-phase AC version suffers a double line frequency torque pulsation, not present in poly-phase motor. Since a commutator motor can operate at much higher speed than an induction motor, it can output more power than a similar size induction motor. However commutator motors are not as maintenance free as induction motors, due to brush and commutator wear.

Single phase series motor
If a DC series motor equipped with a laminated field is connected to AC, the lagging reactance of the field coil will considerably reduce the field current. While such a motor will rotate, operation is marginal. While starting, armature windings connected to commutator segments shorted by the brushes look like shorted transformer turns to the field. This results in considerable arcing and sparking at the brushes as the armature begins to turn. This is less of a problem as speed increases, which shares the arcing and sparking between commutator segments The lagging reactance and arcing brushes are only tolerable in very small uncompensated series AC motors operated at high speed. Series AC motors smaller than hand drills and kitchen mixers may be uncompensated.

Compensated series motor
The arcing and sparking is mitigated by placing a compensating winding the stator in series with the armature positioned so that its magnetomotive force (mmf) cancels out the armature AC mmf. A smaller motor air gap and fewer field turns reduces lagging reactance in series with the armature improving the power factor. All but very small AC commutator motors employ compensating windings. Motors as large as those employed in a kitchen mixer, or larger, use compensated motors.

Universal motor
It is possible to design small (under 300 watts) universal motors which run from either DC or AC. Very small universal motors may be uncompensated. Larger higher speed universal motors use a compensating winding. A motor will run slower on AC than DC due to the reactance encountered with AC. However, the peaks of the sine waves saturate the magnetic path reducing total flux below the DC value, increasing the speed of the "series" motor. Thus, the offsetting effects result in a nearly constant speed from DC to 60 Hz. Small line operated appliances, such as drills, vacuum cleaners, and mixers, requiring 3000 to 10,000 rpm use universal motors. Though, the development of solid state rectifiers and inexpensive permanent magnets is making the DC permanent magnet motor an alternative.

Repulsion motor
A repulsion motor consists of a field directly connected to the AC line voltage and a pair of shorted brushes offset by 15oto 25o from the field axis. The field induces a current flow into the shorted armature whose magnetic field oppose that of the field coils. Speed can be conrolled by rotating the brushes with respect to the field axis. This motor has superior commutation below synchronous speed, inferior commutation above synchronous speed. Low starting current produces high starting torque.

Repulsion start induction motor
When an induction motor drives a hard starting load like a compressor, the high starting torque of the repulsion motor may be put to use. The induction motor rotor windings are brought out to commutator segments for starting by a pair of shorted brushes. At near running speed, a centrifugal switch shorts out all commutator segments, giving the effect of a squirrel cage rotor . The brushes may also be lifted to prolong bush life. Starting torque is 300% to 600% of the full speed value as compared to under 200% for a pure induction motor.

Summary: AC commutator motors

The single phase series motor is an attempt to build a motor like a DC commutator motor. The resulting motor is only practical in the smallest sizes.
The addition of a compensating winding yields the compensated series motor, overcoming excessive commutator sparking. Most AC commutator motors are this type. At high speed this motor provides more power than a same-size induction motor, but is not maintenance free.
It is possible to produce small appliance motors powered by either AC or DC. This is known as a Universal Motor.
The AC line is directly connected to the stator of a repulsion motor with the commutator shorted by the brushes.
Retractable shorted brushes may start a wound rotor induction motor. This is known as a repulsion start induction motor.