Compensated inverse-time undervoltage load shedding systems

A compensated inverse-time undervoltage load shedding system for shedding a load in an electrical power system, the compensated inverse-time undervoltage load shedding system comprising:

• a compensation element for calculating a compensated value from an impedance phasor value;
• and
• an inverse-time undervoltage element in communicating relation with said compensation element, said inverse-time undervoltage element determining a load shedding signal based on a comparison of the compensated value with a predetermined threshold, wherein the load of the electrical power system is shed based on the load shedding signal,
• wherein the impedance phasor value is selected to cause the load to shed more slowly for a measured current of the electrical power system when a measured current value of the measured current is smaller than a selected current value and when the measured current is substantially in phase with a measured voltage of the electrical power system.

A compensated inverse-time undervoltage load shedding system for shedding a load in an electrical power system, the compensated inverse-time undervoltage load shedding system comprising:

• a compensation element for calculating a compensated value, comprising:
• a rate-of-change calculator adapted to calculate a rate-of-change over time;
• and,
• an adder coupled to the rate-of-change calculator, the adder adapted to add the rate-of-change over time to a magnitude to form the compensated value;
• and
• an inverse-time undervoltage element in communicating relation with said compensation element, said inverse-time undervoltage element determining a load shedding signal based on a comparison of the compensated value with a predetermined threshold, wherein the load of the electrical power system is shed based on the load shedding signal,
• wherein a smaller compensated value causes the load to shed more quickly than a larger compensated value.

A compensated inverse-time undervoltage load shedding system for shedding a load in an electrical power system, the compensated inverse-time undervoltage load shedding system comprising:

• a compensation element for calculating a compensated value from an impedance phasor value;
• and
• an inverse-time undervoltage element in communicating relation with said compensation element, said inverse-time undervoltage element determining a load shedding signal based on a comparison of the compensated value with a predetermined threshold, wherein the load of the electrical power system is shed based on the load shedding signal,
• wherein the impedance phasor value is selected to cause the load to shed more quickly when a measured current of the electrical power system lags a measured voltage of the electrical power system than when the measured current does not lag the measured voltage.

A compensated inverse-time undervoltage load shedding system for shedding a load in an electrical power system, the compensated inverse-time undervoltage load shedding system comprising:

• a compensation element for calculating a compensated value from an impedance phasor value;
• and
• an inverse-time undervoltage element in communicating relation with said compensation element, said inverse-time undervoltage element determining a load shedding signal based on a comparison of the compensated value with a predetermined threshold, wherein the load of the electrical power system is shed based on the load shedding signal,
• wherein the impedance phasor value is selected to cause the load to shed more slowly when a measured current of the electrical power system leads a measured voltage of the electrical power system than when the measured current does not lead the measured voltage.

A compensated inverse-time undervoltage load shedding system for shedding a load in an electrical power system, the compensated inverse-time undervoltage load shedding system comprising:

• a compensation element for calculating a compensated value from an impedance phasor value;
• and
• an inverse-time undervoltage element in communicating relation with said compensation element, said inverse-time undervoltage element determining a load shedding signal based on a comparison of the compensated value with a predetermined threshold, wherein the load of the electrical power system is shed based on the load shedding signal,
• wherein the impedance phasor value is selected to cause the load to shed more quickly for a measured current of the electrical power system when a measured current value of the measured current is larger than a selected current value and when the measured current is substantially in phase with a measured voltage of the electrical power system.

A method for undervoltage load shedding with a compensated inverse-time undervoltage load shedding system in an electrical power system, the method comprising:

• calculating a rate-of-change of a magnitude over time;
• adding the rate-of-change of the magnitude over time to the magnitude to form a compensated value;
• enabling the inverse-time undervoltage element based on the compensated value;
• and,
• determining a load shedding signal by comparing the compensated value with a predetermined threshold,
• wherein a load of the electrical power system is shed based on the load shedding signal.

A method for undervoltage load shedding with a compensated inverse-time undervoltage load shedding system in an electrical power system, the method comprising:

• selecting an impedance phasor value to cause the load to shed more quickly when a measured current of the electrical power system lags a measured voltage of the electrical power system than when the measured current does not lag the measured voltage;
• calculating a compensated value from the impedance phasor value;
• enabling the inverse-time undervoltage element based on the compensated value;
• and,
• determining a load shedding signal by comparing the compensated value with a predetermined threshold;
• wherein a load of the electrical power system is shed based on the load shedding signal.

A method for undervoltage load shedding with a compensated inverse-time undervoltage load shedding system in an electrical power system, the method comprising:

• selecting an impedance phasor value to cause the load to shed more slowly when a measured current of the electrical power system leads a measured voltage of the electrical power system than when the measured current does not lead the measured voltage;
• calculating a compensated value from the impedance phasor value;
• enabling the inverse-time undervoltage element based on the compensated value;
• and,
• determining a load shedding signal by comparing the compensated value with a predetermined threshold,
• wherein a load of the electrical power system is shed based on the load shedding signal.

A method for undervoltage load shedding with a compensated inverse-time undervoltage load shedding system in an electrical power system, the method comprising:

• selecting an impedance phasor value to cause the load to shed more quickly for a measured current of the electrical power system when a measured current value of the measured current is larger than a selected current value and when the measured current is substantially in phase with a measured voltage of the electrical power system;
• calculating a compensated value from the impedance phasor value;
• enabling the inverse-time undervoltage element based on the compensated value;
• and,
• determining a load shedding signal by comparing the compensated value with a predetermined threshold,
• wherein a load of the electrical power system is shed based on the load shedding signal.

A method for undervoltage load shedding with a compensated inverse-time undervoltage load shedding system in an electrical power system, the method comprising:

• selecting an impedance phasor value to cause the load to shed more slowly for a measured current of the electrical power system when a measured current value of the measured current is smaller than a selected current value and when the measured current is substantially in phase with a measured voltage of the electrical power system;
• calculating a compensated value from the impedance phasor value;
• enabling the inverse-time undervoltage element based on the compensated value;
• and,
• determining a load shedding signal by comparing the compensated value with a predetermined threshold,
• wherein a load of the electrical power system is shed based on the load shedding signal.

A method for undervoltage load shedding with a compensated inverse-time undervoltage load shedding system in an electrical power system, the method comprising:

• selecting an impedance phasor value to prevent the load from shedding for a measured current of the electrical power system when a measured current value of the measured current is smaller than a selected current value and when the measured current is substantially in phase with a measured voltage of the electrical power system;
• calculating a compensated value from and the impedance phasor value;
• enabling the inverse-time undervoltage element based on the compensated value;
• and,
• determining a load shedding signal by comparing the compensated value with a predetermined threshold,
• wherein a load of the electrical power system is shed based on the load shedding signal.

A method for undervoltage load shedding with a compensated inverse-time undervoltage load shedding system in an electrical power system, the method comprising:

• calculating a current phasor;
• calculating a voltage phasor;
• multiplying the current phasor by an impedance phasor value to form a compensated current value
• calculating a compensated value from the compensated current value;
• subtracting the compensated current value from the voltage phasor to form a compensated voltage value;
• enabling the inverse-time undervoltage element based on the compensated value;
• and,
• determining a load shedding signal by comparing the compensated value with a predetermined threshold,
• wherein a load of the electrical power system is shed based on the load shedding signal, and,
• wherein a smaller compensated voltage value causes the load to shed more quickly than a larger compensated voltage value.

A compensated inverse-time undervoltage load shedding system for shedding a load in an electrical power system, the compensated inverse-time undervoltage load shedding system comprising:

• a compensation element for calculating a compensated value, comprising:
• a current phasor calculator adapted to calculate a current phasor;
• a voltage phasor calculator adapted to calculate a voltage phasor;
• a multiplier coupled to the current phasor calculator and adapted to multiply the current phasor by an impedance phasor value to form the compensated current value;
• and,
• an adder coupled to the current phasor calculator and the voltage phasor calculator and adapted to subtract the compensated current value from the voltage phasor to form a compensated voltage value;
• and
• an inverse-time undervoltage element in communicating relation with said compensation element, said inverse-time undervoltage element determining a load shedding signal based on a comparison of the compensated value with a predetermined threshold, wherein the load of the electrical power system is shed based on the load shedding signal,
• wherein a smaller compensated voltage value causes the load to shed more quickly than a larger compensated voltage value.