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Ground Loop Basics

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

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-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.

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