Symmetrical component amplitude and phase comparators for line protection using time stamped data

• US 8,655,608 B2
• Filed: 09/26/2008
• Issued: 02/18/2014
• Est. Priority Date: 09/28/2007
• Status: Active Grant

• Current Assignee: Schweitzer Engineering Laboratories, Incorporated
• Original Assignee: Schweitzer Engineering Laboratories, Incorporated
• Inventors: Guzman-Casillas, Armando
• Primary Examiner(s): Breene, John
• Assistant Examiner(s): Zhang, Ruihua
• Application Number:
  US12/239,615
• Publication Number:
  US 20090088989A1
• Time in Patent Office: 1,971 Days
• Field of Search: 702/57, 702/58, 702/64, 702/65, 702/79, 361/36, 361/44, 361/45, 361/63
• US Class Current: 702/58
• CPC Class Codes: G01R 31/085 in power transmission or distribution lines, e.g. overhead
• CPC Class Codes: G01R 31/088 Aspects of digital computing
• CPC Class Codes: H02H 7/263 involving transmissions of measured values comparison of currents or voltages using pilot wires H02H3/30
• 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 set of current measurements may be transmitted from a remote Intelligent Electronic Device (IED) to a local IED. The current measurements may comprise a timestamp and/or be associated with timestamp information to allow the local IED to time align the local current measurement with the remote current measurement. The local IED may detect a fault within the power system segment defined by the local and remote IEDs by comparing an operating current to a scaled restraint current. A fault may also be detected by comparing the operating current to a scaled nominal current. The operating and restraint currents may be derived from the local and remote current measurements. The restraint current scale may be derived from the characteristics of the local and/or remote IED. The current measurements may correspond to a negative-sequence component and/or a zero-sequence component of a three-phase current measurement set.

Claims

1. A method for detecting a fault on a conductor by a first intelligent electronic device (IED) monitoring a power system segment having a first IED and a second IED receiving a time signal from a common time reference, comprising:

obtaining a first set of current measurements and associated timestamp from a clock in communication with the common time reference;

the first IED receiving a second set of current measurements and associated timestamp from a clock in communication with the common time reference, from the second IED;

the first IED time aligning the first set of current measurements and the second set of current measurements using the timestamps associated with the first and second sets of current measurements;

calculating a first symmetrical component from the time aligned first set of current measurements;

calculating a second symmetrical component from the time aligned second set of current measurements;

detecting the fault on the conductor using the first and second symmetrical components; and

,

nullifying the fault detection by not asserting a trip signal when an error in the measurements, clock, or time alignment is detected.

2. The method of claim 1, wherein the detecting comprises comparing an operating current to a scaled restraint current, wherein the operating current and scaled restraint current are derived from the time aligned current measurements.

3. The method of claim 1, wherein the detecting further comprises comparing an operating current to a scaled nominal current.

4. The method of claim 3, wherein the first and second symmetrical components comprise negative sequence components.

5. The method of claim 3, wherein the first and second symmetrical components comprise zero sequence components.

6. The method of claim 2, wherein the operating current corresponds to a sum of the time aligned current measurements.

7. The method of claim 2, wherein the scaled restraint current corresponds to a difference of the time aligned current measurements.

8. The method of claim 2, further comprising triggering an output in the power system segment if the operating current is greater than the scaled restraint current.

9. The method of claim 3, wherein the detecting triggers an output in the power system segment if the operating current is greater than the scaled nominal current.

10. The method of claim 2, wherein the scale of the scaled restraint current corresponds to an IED characteristic of the first and second IEDs.

11. The method of claim 1, wherein the detecting comprises comparing a real part of a dot product of the first symmetrical current component and a complex conjugate of the second symmetrical current component to zero.

12. The method of claim 1, wherein the second set of current measurements comprises a set of synchrophasors.

26. The method of claim 1, wherein the step of nullifying the fault detection comprises de-asserting a fault signal.

13. An apparatus for detecting a fault on a conductor by a first IED in a segment of a power system monitored by the first IED and a second IED receiving a time signal from a common time reference, comprising:

a current sensor to obtain a first set of current measurements at the first IED;

a communications interface to receive a second set of current measurements from the second IED, the second set of current measurements comprising a timestamp from a clock in communication with the common time reference;

a comparator to detect a fault in the segment using only a first set of time aligned current measurements derived from the first set of current measurements and a second set of time aligned current measurements derived from the second set of current measurements; and

,

a functional block to nullify the fault detection by not asserting a trip signal when an error in the measurements, clock or time alignment is detected.

14. The apparatus of claim 13, wherein the comparator is configured to time align the first set of current measurements to produce the first set of time aligned current measurements and to time align the second set of current measurements to produce the second set of time aligned current measurements.

15. The apparatus of claim 14, wherein the time aligning comprises modifying a magnitude of the second set of current measurements.

16. The apparatus of claim 15, wherein the first set of current measurement comprises a timestamp, and wherein the time aligning comprises modifying a magnitude of the first set of current measurements.

17. The apparatus of claim 15, wherein the time aligning comprises delaying the first set of current measurements relative to the set of second current measurements.

18. The apparatus of claim 14, wherein the second IED is configured to time align the second set of current measurements to a measurement interval based on a common time reference.

19. The apparatus of claim 18, wherein the current sensor is configured to obtain the first set of current measurements on a measurement interval based on the common time reference.

20. The apparatus of claim 14, wherein the comparator detects a fault in the segment by comparing an operating current to a scaled restraint current, wherein the operating current and scaled restraint current are derived from the first and second set of time aligned current measurements.

21. The apparatus of claim 20, wherein the comparator is configured to trigger a fault in the segment if an amplitude of the operating current is greater than an amplitude of the restraint current scaled by a restraint scale factor.

22. The apparatus of claim 20, wherein the scaled restraint current is further derived from a restraint scale factor that corresponds to a characteristic of the first IED and the second IED.

23. The apparatus of claim 14, wherein the comparator detects a fault in the segment by comparing a dot product of the first time aligned current measurement and a complex conjugate of the second time aligned current measurement to zero.

24. The apparatus of claim 13, wherein first and second sets of current measurements each correspond to one selected from the group consisting of a negative sequence component of a three-phase current, a positive sequence of three-phase current, and a zero component of three-phase current.

25. The apparatus of claim 13, wherein the second set of current measurements comprise a set of a synchrophasors.

27. The apparatus of claim 13, wherein the functional block nullifies the fault detection by de-asserting a fault signal.