Method and device for assessing and monitoring voltage security in a power system

• US 8,498,832 B2
• Filed: 09/26/2008
• Issued: 07/30/2013
• Est. Priority Date: 09/28/2007
• Status: Active Grant

• Current Assignee: Schweitzer Engineering Laboratories, Incorporated
• Original Assignee: Schweitzer Engineering Laboratories, Incorporated
• Inventors: Venkatasubramanian, Vaithianathan
• Primary Examiner(s): Kundu, Sujoy
• Assistant Examiner(s): BETSCH, REGIS J
• Application Number:
  US12/239,637
• Publication Number:
  US 20090085407A1
• Time in Patent Office: 1,768 Days
• Field of Search: 702/60, 702/57, 702/65, 700/291, 700/295
• US Class Current: 702/65
• CPC Class Codes: G05F 1/70 Regulating power factor; Regulating reactive current or power

Abstract

Provided is a method and device for assessing and monitoring voltage security in a power system. More specifically, a method and device for assessing and monitoring the value of reactive power load when changes in reactive power outputs of at least some of the generators in the electrical power system cause all of the generators in the system to reach the combined operating limit of their reactive power output. In response thereto, the method and device are further adapted to initiate suitable control measures such as switching of transformer banks and/or capacitor/reactor banks, as well as shedding loads whenever necessary to mitigate an impending voltage stability problem.

Claims

1. A device for assessing and monitoring voltage stability in an electrical power system including a plurality of generators and phasor measurement units, said phasor measurement units adapted to acquire and communicate phasor measurements from various locations on the power system, the device comprising:

a communications port adapted to receive the phasor measurements from the phasor measurement units,

a predictive reactive power load limit calculator to calculate a reactive power loading margin where the plurality of generators will reach their respective and combined reactive power limits using a small number of power-flow runs, the calculator in communication with the communications port and receiving the phasor measurements, and the calculator adapted to;

calculate a predictive generator reactive power sensitivity indicating an anticipated change in generation reactive power output resulting from a predictive change in reactive power load at a specified reactive power load using the phasor measurements, wherein the magnitude of the sensitivity is related to the proximity to a static limit;

determine, based on the sensitivity, a load increment used for calculating the specified reactive power load for the next power-flow run, and,

when the sensitivity is not less than a threshold, calculate the reactive power loading margin as a difference between the specified reactive power load and a current reactive power load.

2. The device of claim 1 further comprising an apparatus for reducing the reactive power load at one or more of the generators.

3. The device of claim 2 wherein the apparatus is a load shedding apparatus.

4. The device of claim 1 further comprising an apparatus for increasing or decreasing reactive power outputs of some of the generators.

5. The device of claim 1 further comprising an apparatus for accelerating the calculation processing of the predictive reactive power load limit calculator.

6. The device of claim 1 further including a generator reactive power sensitivity calculator.

7. The device of claim 6 wherein the generator reactive power sensitivity calculator is based at least in part on power-flow Jacobian.

8. The device of claim 1 further comprising an alarm coupled to the predictive reactive power load limit calculator adapted to indicate when a plurality of generators in the electrical power system have reached their combined maximum operating limit of providing reactive power.

9. The device of claim 1 further comprising a signaling circuit coupled to the predictive reactive power load limit calculator adapted to provide a signal representative of a control or monitoring action when a plurality of generators in the electrical power system have reached their combined maximum operating limit of providing reactive power.

10. The device of claim 1 wherein the communications port is adapted to receive Supervisory Control and Data Acquisition (SCADA) measurements, and the predictive reactive power load limit calculator is adapted to calculate a reactive power loading margin based in part on the SCADA measurements.

18. The device of claim 1, wherein the predictive reactive power load limit calculator is adapted to calculate a predictive generator reactive power sensitivity by evaluating a power-flow solution.

19. The device of claim 1, wherein the predictive reactive power load limit calculator is adapted to calculate a predictive generator reactive power sensitivity at a particular bus by evaluating a number of power flow solutions.

21. The device of claim 19, wherein the reactive power loading margin comprises a reactive power loading margin at the particular bus calculated as a difference between the reactive power load at the particular bus and the predictive change in reactive power load at the particular bus when the next generator will cause the plurality of generators to reach a combined reactive power operating limit.

23. The device of claim 1, wherein the static limit comprises a nose of a QV curve.

25. The device of claim 1, wherein the calculator is further adapted to calculate a plurality of power-flow solutions at a plurality of different reactive power loads, and wherein the sensitivity is calculated based on the incremental difference between a second reactive power generated at a second of the plurality of different reactive power loads and a first reactive power generated at a first of the plurality of different reactive power loads.

26. The device of claim 1, wherein the calculator is adapted to directly calculate the sensitivity when it is assumed only reactive power load is changing using a sensitivity equation:

27. The device of claim 1, wherein the calculator is adapted to directly calculate the sensitivity when real and reactive load powers are changing using a first sensitivity equation:

11. A method for assessing and monitoring voltage stability in an electrical power system including a plurality of generators, including the steps of:

a voltage security processor acquiring phasor or Supervisory Control and Data Acquisition (SCADA) measurements from various locations on the power system,

calculating, using the voltage security processor, a reactive power loading margin where the plurality of generators will reach their respective and combined reactive power limits using a small number power-flow runs, at least one power-flow run comprising;

calculating a predictive generator reactive power sensitivity indicating an anticipated change in generation reactive power output resulting from a predictive change in reactive power load at a specified reactive power load using the measurements, wherein the magnitude of the sensitivity is related to the proximity to a static limit,

determining, based on the sensitivity, a load increment used for calculating the specified reactive power load for the next power-flow run, and,

when the sensitivity is not less than a threshold, calculating the reactive power loading margin as a difference between the specified reactive power load and a current reactive power load.

12. The method of claim 11 further comprising the step of reducing the reactive power load at one or more of the generators.

13. The method of claim 11 further comprising the step of increasing the reactive power outputs of some of the generators.

14. The method of claim 11 further comprising the step of decreasing the reactive power outputs of some of the generators.

15. The method of claim 11 wherein the generator reactive power sensitivity is calculated based at least in part on power-flow Jacobian.

16. The method of claim 11 further comprising the step of signaling an alarm to indicate when a plurality of generators in the electrical power system have reached their combined maximum operating limit of providing reactive power.

17. The method of claim 11, wherein the step of calculating a predictive generator reactive power sensitivity comprises evaluating a power-flow solution.

20. The method of claim 11, wherein the step of calculating a predictive generator reactive power sensitivity comprises calculating the sensitivity at a particular bus by evaluating a number of power flow solutions.

22. The method of claim 20, wherein the reactive power loading margin comprises a reactive power loading margin at the particular bus, and the step of calculating the reactive power loading margin comprises calculating as a difference between the reactive power load at the particular bus and the predictive change in reactive power load at the particular bus when the next generator will cause the plurality of generators to reach a combined reactive power operating limit.

24. The method of claim 11, wherein the static limit comprises a nose of a QV curve.