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 as
The 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.
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 as
The 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) 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%).
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%).
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Energy Regulatory COmmision
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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
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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
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Events in Electrical Network, Requirements for LVRT Capability in NationalGrid COdes, Fault Analysis, General Conclusion.
Download pdf
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Download pdf
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Beginning Special Applications Wiring
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