Minimizing circulating current using time-aligned data

• US 8,321,162 B2
• Filed: 01/28/2010
• Issued: 11/27/2012
• Est. Priority Date: 10/09/2007
• Status: Active Grant

• Current Assignee: Schweitzer Engineering Laboratories, Incorporated
• Original Assignee: Schweitzer Engineering Laboratories, Incorporated
• Inventors: Labuschagne, Casper A., Fischer, Normann, Samineni, Satish, Guzman-Casillas, Armando
• Primary Examiner(s): Raymond, Edward
• Application Number:
  US12/695,778
• Publication Number:
  US 20100125373A1
• Time in Patent Office: 1,034 Days
• Field of Search: 702/60, 702/66, 702182-185, 702/188
• US Class Current: 702/60
• CPC Class Codes: G01R 19/2513 Arrangements for monitoring electric power systems, e.g. power lines or loads; Logging
• CPC Class Codes: H02J 3/1878 using tap changing or phase shifting transformers
• CPC Class Codes: H02J 3/46 Controlling of the sharing of output between the generators, converters, or transformers
• CPC Class Codes: H02P 13/06 by tap-changing; by rearranging interconnections of windings
• CPC Class Codes: Y02E 40/30 Reactive power compensation
• CPC Class Codes: Y02E 40/70 Smart grids as climate change mitigation technology in the energy generation sector
• CPC Class Codes: Y02E 60/00 Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
• CPC Class Codes: Y04S 10/00 Systems supporting electrical power generation, transmission or distribution
• CPC Class Codes: Y04S 10/22 Flexible AC transmission systems [FACTS] or power factor or reactive power compensating or correcting units

Abstract

A power system may comprise two or more transformers operating in parallel. A voltage differential may exist between the transformers, which may create a circulating current in the power system. The system voltage of the power system may be modified by performing a tap change operation on one or more of the transformers. The tap change operation may be configured to minimize the circulating current. The circulating current may be minimized by determining the bias between the transformers using an angular difference between the transformer currents. The angular difference may be calculated using time-aligned measurement data. A tap change operation configured to modify the system voltage, while minimizing circulating current, may be determined using the transformer bias.

Claims

1. A device for performing a tap change operation in an electrical power system comprising a first transformer and a second transformer operating in parallel, the tap change operation to modify a system voltage of the electrical power system, the device comprising:

a processor;

a communications interface configured to receive a first current phasor measurement of a current of the first transformer; and

a tap change control module operable on the processor and in communication with the communications interface, the tap change control module configured to;

time align the first and the second current phasor measurements;

determine an angle difference between the first current phasor measurement and a second current phasor measurement of a current of the second transformer, wherein the angle difference is calculated using the time-aligned measurements; and

to

generate a tap change command based upon the angle difference, the tap change command configured to modify the system voltage.

2. The device of claim 1, wherein the tap change command is configured to cause one of the first and the second transformers to modify a tap setting thereof.

3. The device of claim 1, wherein the first and the second current phasor measurements comprise respective time stamps.

4. The device of claim 1, wherein the first current phasor measurement is a synchrophasor.

5. The device of claim 1, wherein the tap change control module is configured to raise the system voltage, wherein the angle difference is calculated by subtracting an angle of the second current phasor measurement from an angle of the first current phasor measurement, and

wherein when the angle difference is greater than zero, the tap change command is configured to cause the first transformer to raise the system voltage, and when the angle difference is not greater than zero, the tap change command is configured to cause the second transformer to raise the system voltage.

6. The device of claim 5, wherein the tap change command is configured to increase a tap setting of the first transformer.

7. The device of claim 1, wherein the tap change control module is configured to lower the system voltage, wherein the angle difference is calculated by subtracting an angle of the second current phasor measurement from an angle of the first current phasor measurement, and

wherein when the angle difference is greater than zero, the tap change command is configured to cause the second transformer to lower the system voltage, and wherein when the angle difference is not greater than zero, the tap change command is configured to cause the first transformer to lower the system voltage.

8. The device of claim 7, wherein the tap change command is configured to decrease a tap setting of the second transformer.

9. The device of claim 1, wherein the communications interface is configured to transmit a tap change command generated by the tap change control module to one of the first transformer and the second transformer.

10. The device of claim 1, wherein the device receives measurements of the system voltage, and wherein the tap change control module is configured to generate a tap change command based on the system voltage measurements.

11. The device of claim 10, wherein the tap change control module is configured to generate a tap change command configured to raise the system voltage when the measurements of the system voltage fall below a lower bound.

12. The device of claim 10, wherein the tap change control module is configured to generate a tap change command configured to lower the system voltage when the measurements of the system voltage exceed an upper bound.

13. The device of claim 1, wherein the first transformer and the second transformer are located within a single substation.

14. The device of claim 1, wherein the first transformer and the second transformer are located in separate substations.

15. A method for performing a tap change operation configured to modify a system voltage and minimize circulating current in an electrical power system, the electrical power system comprising a first transformer and a second transformer operating in parallel, the method comprising:

receiving first current phasor measurements of a current of the first transformer, the first current phasor measurements acquired by a first current transformer;

receiving second current phasor measurements of a current of the second transformer, the second current phasor measurements acquired by a second current transformer;

time aligning the first and the second current phasor measurements;

calculating an angle difference between the time-aligned first and second current phasor measurements; and

generating a tap change command based on the angle difference, the tap change command configured to cause one of the first and the second transformers to modify the system voltage by changing a tap setting thereof.

16. The method of claim 15, further comprising transmitting the tap change command to one of the first and the second transformers.

17. The method of claim 15, wherein the first current phasor measurements comprise synchrophasors.

18. The method of claim 15, wherein the first and the second phasor measurements are associated with time-stamp information, and wherein the first and the second phasor measurements are time aligned using the time-stamp information.

19. The method of claim 15, further comprising:

receiving measurements of the system voltage;

generating a tap change command configured to lower the system voltage when the system voltage measurements exceed an upper bound; and

generating a tap change command configured to raise the system voltage, when the system voltage measurements fall below a lower bound.

20. The method of claim 15, wherein the tap change command is configured to raise the system voltage, wherein the angle difference is calculated by subtracting an angle of the second current phasor measurements from an angle of the first current phasor measurements, and wherein generating the tap change command comprises:

when the angle difference is greater than zero, configuring the tap change command to cause the first transformer to increase the system voltage; and

when the angle difference is not greater than zero, configuring the tap change command to cause the second transformer to increase the system voltage.

21. The method of claim 20, wherein the tap change command is configured to increase a tap setting of the first transformer.

22. The method of claim 15, wherein the tap change command is configured to lower the system voltage, wherein the angle difference is calculated by subtracting an angle of the second current phasor measurements from an angle of the first current phasor measurements, and wherein generating the tap change command comprises:

when the angle difference is greater than zero, configuring the tap change command to cause the second transformer to lower the system voltage;

when the angle difference is not greater than zero, configuring the tap change command to cause the first transformer to lower the system voltage.

23. The method of claim 22, wherein the tap change command is configured to lower a tap setting of the second transformer.

24. The method of claim 15, wherein the first transformer and the second transformer are located within a single substation.

25. The method of claim 15, wherein the first transformer and the second transformer are located in separate substations.

26. A system for performing a tap change operation configured to modify a system voltage of an electrical power system comprising a first transformer and a second transformer operating in parallel, the system comprising:

a first intelligent electronic device (IED) configured to acquire current phasor measurements of a current of the first transformer;

a second IED configured to acquire current phasor measurements of a current of the second transformer; and

a data processor configured to receive the first and the second current phasor measurements, to time-align the first and the second current phasor measurements, and to calculate an angle difference therebetween by subtracting an angle of the second current phasor measurements from an angle of the first current phasor measurements,

wherein to raise the system voltage, the data processor is configured to generate a tap change control command configured to cause the first transformer to increase the system voltage when the angle difference is greater than zero, and to generate a tap change control command configured to cause the second transformer to increase the system voltage when the angle difference is not greater than zero, and

wherein to lower the system voltage, the data processor is configured to generate a tap change control command configured to cause the second transformer to lower the system voltage when the angle difference is greater than zero, and to generate a tap change control command configured to cause the first transformer to lower the system voltage when the angle difference is not greater than zero.

27. The system of claim 26, wherein the first and the second current phasor measurements are associated with time-stamp information, and wherein the first and the second current phasor measurements are time aligned using the time-stamp information.

28. The system of claim 26, wherein the first and second current phasor measurements comprise synchrophasors.

29. The system of claim 26, further comprising a communications interface configured to transmit a tap change command generated by the data processor to one of the first and the second transformers.