Method and component for voltage instability protection in an electric power system

1. A method of protecting an electric power system against voltage instability, the method comprising:

determining a change in power injected into a region of interest within the electric power system based on synchronized power measurements from different power injection points of the region of interest;

determining a change in power absorbed by one or more loads in the region of interest based on synchronized power measurements from different load points of the region of interest;

determining a change in power loss for the region of interest based on the difference between the change in power injected into the region of interest and the change in power absorbed by the region of interest;

indicating a voltage instability condition when the change in power loss for the region of interest approximates the change in power injected into the region of interest; and

controlling one or more protective devices based on determining the voltage instability.

2. The method according to claim 1 , wherein the power injection points comprise at least one of border points at a boundary of the region of interest and power generators located within the region of interest.

3. The method according to claim 2 , wherein the electric power system has one or more dominant lines which deliver the majority of the injected power to the region of interest, and wherein only the border points connected to the dominant lines are monitored to determine the change in power injected into the region of interest.

4. The method according to claim 1 , wherein each power injection point and each load point has an intelligent electronic device for measuring power, and wherein the synchronized power measurements are obtained from the intelligent electronic devices.

5. The method according to claim 1 , wherein the change in power loss for the region of interest, the change in power injected into the region of interest, and the change in power absorbed by the region of interest are calculated for a present evaluation period when the power injected into the region of interest changes by more than a predetermined amount from an immediately preceding evaluation period to the present evaluation period.

6. The method according to claim 1 , wherein indicating a voltage instability condition comprises:

calculating a loss index as a function of the change in power loss for the region of interest and the change in power injected into the region of interest; and

setting an alarm when the loss index violates an alarm threshold.

7. The method according to claim 6 , wherein the loss index is a real number between zero and two, and wherein a voltage collapse within the region of interest is more likely the closer the loss index is to zero.

8. The method according to claim 6 , further comprising forcing one or more protective devices in the electric power system to open into a protective state so that the region of interest is isolated from the remainder of the electric power system when the loss index violates a trip threshold which is different than the alarm threshold.

9. The method according to claim 8 , wherein the one or more protective devices are forced to open into the protective state if the loss index violates the trip threshold for a predetermined time period.

10. The method according to claim 6 , wherein calculation of the loss index for a present evaluation period is skipped if the power injected into the region of interest changes by less than a predetermined amount from an immediately preceding evaluation period to the current evaluation period.

11. A component of an electric power system, comprising:

a controller operable to:

determine a change in power injected into a region of interest within the electric power system based on synchronized power measurements from different power injection points of the region of interest;

determine a change in power absorbed by one or more loads in the region of interest based on synchronized power measurements from different load points of the region of interest; and

determine a change in power loss for the region of interest based on the difference between the change in power injected into the region of interest and the change in power absorbed by the region of interest; and

a transmitter operable to indicate a voltage instability condition when the change in power loss for the region of interest approximates the change in power injected into the region of interest;

wherein the controller controls one or more protective devices based on determining the voltage instability.

12. The component according to claim 11 , wherein the component comprises an intelligent electronic device including the controller and the transmitter, and wherein the intelligent electronic device is operable to measure power at one of the power injection points or the load points.

13. The component according to claim 12 , wherein the intelligent electronic device is included in a border point at a boundary of the region of interest or a power generator located within the region of interest.

14. The component according to claim 11 , wherein each power injection point and each load point has an intelligent electronic device for measuring power, wherein the synchronized power measurements are obtained from the intelligent electronic devices, and wherein the component is one of the intelligent electronic devices.

15. The component according to claim 11 , wherein the controller is operable to calculate the change in power loss for the region of interest, the change in power injected into the region of interest, and the change in power absorbed by the region of interest for a present evaluation period when the power injected into the region of interest changes by more than a predetermined amount from an immediately preceding evaluation period to the present evaluation period.

16. The component according to claim 11 , wherein the controller is operable to calculate a loss index as a function of the change in power loss for the region of interest and the change in power injected into the region of interest, and set an alarm indicating a voltage instability condition when the loss index violates an alarm threshold.

17. The component according to claim 16 , wherein the loss index is a real number between zero and two, and wherein a voltage collapse within the region of interest is more likely the closer the loss index is to zero.

18. The component according to claim 16 , wherein the controller is operable to force one or more protective devices in the electric power system to open into a protective state so that the region of interest is isolated from the remainder of the electric power system when the loss index violates a trip threshold which is different than the alarm threshold.

19. The component according to claim 18 , wherein the controller is operable to force the one or more protective devices to open into the protective state if the loss index violates the trip threshold for a predetermined time period.

20. The component according to claim 16 , wherein the controller is operable to skip the calculation of the loss index for a present evaluation period if the power injected into the region of interest changes by less than a predetermined amount from an immediately preceding evaluation period to the current evaluation period.