ISLANDING DETECTION IN AN ELECTRICAL POWER DELIVERY SYSTEM

• US 20100286838A1
• Filed: 05/10/2010
• Published: 11/11/2010
• Est. Priority Date: 05/11/2009
• Status: Active Grant

• Current Assignee: Schweitzer Engineering Laboratories, Incorporated
• Original Assignee: Schweitzer Engineering Laboratories, Incorporated
• Inventors: Mynam, Mangapathirao Venkat, Donolo, Marcos A., Guzman-Casillas, Armando
• Granted Patent: US 8,346,402 B2
• Time in Patent Office: Days
• US Class Current: 700/293
• CPC Class Codes: G01R 19/2513 Arrangements for monitoring electric power systems, e.g. power lines or loads; Logging
• CPC Class Codes: H02J 3/388 Islanding, i.e. disconnection of local power supply from the network

Abstract

An intelligent electronic device is operable to use a signal derived from an electrical power delivery system to effectively detect an islanding condition. The intelligent electronic device is configured to compare a frequency deviation (from nominal frequency) and a rate-of-change of frequency of the electrical power delivery system to a protection characteristic of the intelligent electronic device to quickly and securely detect islanding conditions thereby enhancing power protection, automation, control, and monitoring performance. The intelligent electronic device uses local measurements of the electrical power deliver system to provide reliable and economical means to properly separate a generation site from the remainder of the electrical power delivery system. Such may be useful to prevent reclosing out of synchronism.

Claims

1. An intelligent electronic device for detecting an islanding condition in an electrical power delivery system, comprising:

an input for receiving a signal of the electrical power delivery system;

a processing unit configured to detect an islanding condition based on the signal, the processing unit being operable to determine from the signal a frequency deviation of electrical power delivery system from nominal frequency and a rate-of-change of frequency of the electrical power delivery system, the frequency deviation and the rate-of-change of frequency defining an operating point of the electrical power delivery system, the processing unit being operable to compare the operating point to a protection characteristic of the intelligent electronic device, wherein the processing unit is operable to issue a command based upon the comparison; and

an output in communication with the processing unit to communicate the command from the processing unit.

2. The intelligent electronic device of claim 1, wherein the protection characteristic is derived by settings representing selected frequency deviation and rate-of-change of frequency values.

3. The intelligent electronic device of claim 2, wherein the settings include a first setting representing a first frequency deviation value, a second setting representing a second frequency deviation value, a third setting representing a first rate-of-change of frequency value, and a fourth setting representing a second rate-of-change of frequency value.

4. The intelligent electronic device of claim 3, wherein the processing unit is operable to compare the operating point to a trip region of the protection characteristic derived from the first, second, third, and fourth settings.

5. The intelligent electronic device of claim 4, wherein the trip region comprises a first boundary derived from a function of the form

6. The intelligent electronic device of claim 5, wherein the trip region includes a second boundary corresponding to the first frequency deviation value represented by the first trip setting, and the processing unit is operable to compare the operating point to the second boundary.

7. The intelligent electronic device of claim 6, wherein the trip region includes a third boundary corresponding to the first rate-of-change of frequency value represented by the third trip setting, and the processing unit is operable to compare the operating point to the third boundary.

8. The intelligent electronic device of claim 4, wherein the trip region comprises a first boundary derived from a function of the form

9. The intelligent electronic device of claim 3, wherein the protection characteristic includes a trip region defined in a plane that includes a frequency deviation axis and a rate-of-change of frequency axis transverse to the frequency deviation axis, the trip region being derived from the first, second, third, and fourth, trip settings.

10. The intelligent electronic device of claim 9, wherein the trip region includes a boundary line derived from the first, second, third, and fourth trip settings.

11. The intelligent electronic device of claim 10, wherein the boundary line includes a line segment between first and second boundary points in the plane, the first boundary point having coordinates corresponding to the first and fourth trip settings, and the second boundary point having coordinates corresponding to the second and third trip settings.

12. The intelligent electronic device of claim 11, wherein the boundary line is a straight line.

13. The intelligent electronic device of claim 11, wherein the boundary line has a negative slope.

14. The intelligent electronic device of claim 11, wherein the trip region is a first trip region, and the protection characteristic includes a second trip region defined in the plane, the second trip region being derived from the first, second, third, and fourth trip settings.

15. The intelligent electronic device of claim 14, wherein the second trip region includes a boundary line derived from the first, second, third, and fourth trip settings.

16. The intelligent electronic device of claim 15, wherein the boundary line of the second trip region is parallel to the boundary line of the first trip region.

17. The intelligent electronic device of claim 15, wherein the protection characteristic includes a stable operation region provided between the boundary lines of the first and second trip regions to prevent stable frequency oscillations of the electrical power delivery system from generating trip commands.

18. The intelligent electronic device of claim 2, wherein the settings include a first setting representing a frequency deviation value and a second setting representing a

rate of change of frequency value, the protection characteristic including a trip region derived from the first and second settings, and the processing unit being operable to compare the operating point to the trip region.

19. The intelligent electronic device of claim 18, wherein the trip region includes a boundary derived from a function of the form

20. The intelligent electronic device of claim 18, wherein the trip region is defined in a plane that includes a frequency deviation axis and a rate-of-change of frequency axis transverse to the frequency deviation axis, the trip region including a boundary line extending between first and second boundary points in the plane, the first boundary point having a coordinate corresponding to the first setting, and the second boundary point having a coordinate corresponding to the second setting.

21. The intelligent electronic device of claim 1, wherein the signal corresponds to a voltage of the electrical power delivery system.

22. The intelligent electronic device of claim 1, wherein the signal corresponds to a current of the electrical power delivery system.

23. The intelligent electronic device of claim 1, wherein the processing unit is operable to issue the command when a fault detector of the electrical power delivery system has not detected a system fault.

24. The intelligent electronic device of claim 23, wherein the fault detector represents a system operating in the intelligent electronic device.

25. The intelligent electronic device of claim 23, wherein the fault detector represents a system operating on another device.

26. The intelligent electronic device of claim 1, wherein

the output comprises a trip output and the command comprises a trip command, and

the trip output is further in communication with a circuit breaker to communicate the trip command from the processing unit to the circuit breaker.

27. The intelligent electronic device of claim 1, wherein

the output comprises an alarm output and the command comprises an alarm command, and

the alarm output is further in communication with a communications interface to communicate the alarm command from the processing unit to the communications interface.

28. A method of detecting an islanding condition in an electrical power delivery system, comprising:

receiving a signal derived from the electrical power delivery system;

calculating in an intelligent electronic device a frequency deviation of the electrical power delivery system from nominal frequency based on the signal;

calculating in the intelligent electronic device a rate-of-change of frequency of the electrical power delivery system based on the signal, the frequency deviation and the rate-of-change of frequency defining an operating point of the electrical power delivery system; and

comparing the operating point to a protection characteristic of the intelligent electronic device to determine whether an islanding condition has occurred.

29. The method of claim 28, wherein the protection characteristic includes settings representing selected frequency deviation and rate-of-change of frequency values.

30. The method of claim 29, further comprising deriving a trip region of the protection characteristic value from the settings.

31. The method of claim 30, wherein the settings include a first setting SET1 representing a first frequency deviation value, a second setting SET2 representing a second frequency deviation value, a third setting SET3 representing a first rate-of-change of frequency value, and a fourth setting SET4 representing a second rate-of-change of frequency value, and the trip region is derived from a function of the form

32. The method of claim 31, further comprising:

comparing the operating point against the trip region; and

generating a trip command when the operating point is within the trip region.

33. The method of claim 32, further comprising generating the trip command when the operating point is within the trip region for a selected period of time.

34. The method of claim 32, further comprising:

detecting whether a fault has occurred in the electrical power delivery system; and

transmitting the trip command to a circuit breaker when a fault has not been detected.

35. The method of claim 32, wherein the trip region is a first trip region, further comprising:

deriving a second trip region from a function of the form