Apparatus and method for estimating synchronized phasors at predetermined times referenced to an absolute time standard in an electrical system

• US 7,480,580 B2
• Filed: 08/15/2006
• Issued: 01/20/2009
• Est. Priority Date: 10/18/2005
• Status: Active Grant

• Current Assignee: Schweitzer Engineering Laboratories, Incorporated
• Original Assignee: Schweitzer Engineering Laboratories, Incorporated
• Inventors: Anderson, Luther S., Zweigle, Gregary C., Guzman-Casillas, Armando
• Primary Examiner(s): Bui; Bryan
• Application Number:
  US11/504,788
• Publication Number:
  US 20070086134A1
• Time in Patent Office: 889 Days
• Field of Search: 702/60, 702/72, 702/75, 702/106, 702/62, 702/89, 361/85, 361/93.1, 361/115, 361/80
• US Class Current: 702/106
• CPC Class Codes: G01R 19/2513 Arrangements for monitoring electric power systems, e.g. power lines or loads; Logging
• 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

An apparatus and method estimates a plurality of synchronized phasors at predetermined times referenced to an absolute time standard in an electrical power system. The method includes acquiring and determining a frequency of a power system signal, sampling the power system signal at a sampling interval rate based on a frequency of the power system signal to form signal samples, and generating a plurality of acquisition time values based on an occurrence of each of the signal samples at a corresponding plurality of different times referenced to the absolute time standard. The method further includes adjusting a phasor of each of the signal samples based on a time difference between a corresponding selected acquisition time value and a predetermined time referenced to an absolute time standard to form the plurality of synchronized phasors.

Claims

1. An apparatus for estimating a plurality of synchronized phasors at predetermined times referenced to an absolute time standard in an electrical power system, the apparatus comprising:

a sample controller configured to determine a frequency of a power system signal acquired at a location of the electrical power system;

a sampling means configured to sample the electrical power system signal at a sampling interval rate based on the frequency of the power system signal to form a plurality of signal samples;

a time controller configured to generate a plurality of acquisition time values based on an occurrence of each of the plurality signal samples at a corresponding plurality of sample times referenced to the absolute time standard, each of the plurality of acquisition time values associated with a phasor magnitude and a phasor phase angle of each of the plurality of signal samples; and

a phasor estimator configured to adjust the phasor magnitude and the phasor phase angle for each of the plurality of signal samples based on a time difference between a corresponding selected acquisition time value of the plurality of acquisition time values and a predetermined time of the predetermined times referenced to the absolute time standard to form the plurality of synchronized phasors.

2. The apparatus of claim 1, wherein each of the plurality of synchronized phasors comprises a corresponding plurality of referenced phasor magnitudes and referenced phasor phase angles.

3. The apparatus of claim 2, wherein the phasor estimator is further configured to:

interpolate each of the plurality of phasor magnitudes to form each of the plurality of referenced phasor magnitudes; and

rotate each of the plurality of phasor phase angles to form each of the plurality of referenced phasor phase angles.

4. The apparatus of claim 2, further comprising a digital filter to generate a plurality of filtered signals, wherein the phasor estimator is further configured to phase shift each of the plurality of filtered signals by 90 degrees and interpolate prior to calculating reference phasor magnitudes and referenced phasor phase angles.

5. The apparatus of claim 2, further comprising a phasor calculator configured to calculate an uncalibrated referenced phasor magnitude and a prealigned referenced phasor phase angle of each of the plurality of signal samples at the plurality of acquisition time values prior to adjusting the phasor magnitude and the phasor phase angle to the corresponding plurality of referenced phasor magnitudes and referenced phasor phase angles.

6. The apparatus of claim 1, wherein the time difference comprises a difference in time between an occurrence of a preceding selected acquisition time value of the plurality of acquisition time values and a predetermined time of the predetermined times referenced to the absolute time standard.

7. The apparatus of claim 1, wherein the time difference comprises a difference in time between an occurrence of a predetermined time of the predetermined times referenced to the absolute time standard and a next selected acquisition time value of the plurality of acquisition time values.

8. The apparatus of claim 1, wherein the predetermined times are synchronized across the electrical power system.

9. The apparatus of claim 1, wherein the predetermined times are determined local to the apparatus.

10. The apparatus of claim 1, wherein the phasor estimator is further configured to phase align each of the plurality of synchronized phasors to a reference phasor with a predetermined phase and frequency.

11. The apparatus of claim 10, wherein the predetermined frequency comprises 60 Hz.

12. The apparatus of claim 10, wherein the predetermined frequency comprises 50 Hz.

13. The apparatus of claim 1, wherein the power system signal comprises a plurality of power system signals.

14. The apparatus of claim 1, further comprising an analog filter configured to filter the power system signal prior to receipt by the sampling means.

15. The apparatus of claim 1, wherein the absolute time standard is based on a global positioning system signal communicated via an IRIG timecode protocol.

16. The apparatus of claim 1, further comprising a digital filter configured to digitally filter each of the plurality of signal samples.

17. The apparatus of claim 1, wherein the sampling interval rate is an integer multiple of the frequency of the power system signal.

18. The apparatus of claim 1, further comprising utilizing one or more of the plurality of synchronized phasors to perform a power system function selected from the group consisting of:

protection;

automation;

metering;

control; and

combinations thereof.

19. The apparatus of claim 1, wherein the sample controller is further configured to generate a sample frequency signal based on the sampling interval rate, the sample frequency signal aligned with the plurality of acquisition time values and utilized to form the plurality of synchronized phasors.

20. The apparatus of claim 2, wherein the phasor estimator is further configured to:

remove implementation magnitude distortion from the sample frequency signal prior to forming each of the plurality of synchronized phasors; and

remove implementation phase angle distortion from the sample frequency signal prior to forming each of the plurality of synchronized phasors.

21. The apparatus of claim 1, wherein the location of the power system signal is local and the power system signal comprises a local analog input signal.

22. The apparatus of claim 1, wherein the location of the power system signal is remote and the power system signal comprises a digitized remote analog input signal.

23. The apparatus of claim 1, wherein each of the plurality of synchronized phasors comprises a corresponding plurality of referenced phasor sequence quantities.

24. A method for estimating a plurality of synchronized phasors at predetermined times referenced to an absolute time standard in an electrical power system, the method comprising:

determining a frequency of a power system signal;

sampling the power system signal at a sampling interval rate based on the frequency of the power system signal to form a plurality of signal samples;

generating a plurality of acquisition time values based on an occurrence of each of the plurality signal samples at a corresponding plurality of sample times referenced to the absolute time standard, each of the plurality of acquisition time values associated with a phasor magnitude and a phasor phase angle of each of the plurality of signal samples; and

for each of the plurality of signal samples, adjusting the phasor magnitude and the phasor phase angle based on a time difference between a corresponding selected acquisition time value of the plurality of acquisition time values and a predetermined time of the predetermined times referenced to the absolute time standard to form the plurality of synchronized phasors.

25. The method of claim 24, wherein each of the plurality of synchronized phasors comprises a corresponding plurality of referenced phasor magnitudes and referenced phasor phase angles.

26. The method of claim 25, wherein each of the plurality of phasor magnitudes is interpolated to form each of the plurality of referenced phasor magnitudes.

27. The method of claim 25, further comprising the steps of filtering to generate a plurality of filtered signals;

phase shifting each of the plurality of filtered signals by 90 degrees;

interpolating; and

calculating reference phasor magnitudes and referenced phasor angles.

28. The method of claim 25, further comprising the step of calculating an uncalibrated referenced phasor magnitude and a prealigned phasor phase angle of each of the plurality of signal samples at the plurality of acquisition time values prior to adjusting the phasor magnitude and the phasor phase angle to the corresponding plurality of referenced phasor magnitudes and referenced phasor phase angles.

29. The method of claim 25, wherein each of the plurality of phasor phase angles is rotated to form each of the plurality of referenced phasor phase angles.

30. The method of claim 25, further comprising calculating the phasor magnitude and phasor phase angle of each of the plurality of signal samples at the plurality of acquisition time values prior to adjusting the phasor magnitude and the phasor phase angle of each of the plurality of signal samples to the corresponding plurality of referenced phasor magnitudes and referenced phasor phase angles.

31. The method of claim 24, wherein the time difference comprises a difference in time between an occurrence of a preceding selected acquisition time value of the plurality of acquisition time values and a predetermined time of the predetermined times referenced to the absolute time standard.

32. The method of claim 24, wherein the time difference comprises a difference in time between an occurrence of a predetermined time of the predetermined times referenced to the absolute time standard and a next selected acquisition time value of the plurality of acquisition time values.

33. The method of claim 24, wherein the predetermined times are synchronized across the electrical power system.

34. The method of claim 24, wherein the predetermined times are determined at a location on the electrical power system local to the step of determining a frequency of the power system is performed.

35. The method of claim 24, wherein each of the plurality of synchronized phasors is further phase aligned to a reference phasor with predetermined phase and frequency.

36. The method of claim 35, wherein the predetermined frequency comprises 60 Hz.

37. The method of claim 35, wherein the predetermined frequency comprises 50 Hz.

38. The method of claim 24, wherein the power system signal comprises a plurality of power system signals.

39. The method of claim 24, wherein the power system signal is analog filtered prior to the step of sampling.

40. The method of claim 24, wherein the absolute time standard is based on a global positioning system signal communicated via an IRIG timecode protocol.

41. The method of claim 24, wherein each of the plurality of signal samples are digitally filtered.

42. The method of claim 24, wherein the sampling interval rate is an integer multiple of the frequency of the power system signal.

43. The method of claim 24, further comprising utilizing one or more of the plurality of synchronized phasors to perform a power system function selected from the group consisting of:

protection, automation, metering, control, and combinations thereof.

44. The method of claim 24, further comprising generating a sample frequency signal based on the sampling interval rate, the sample frequency signal aligned with the plurality of acquisition time values and utilized to form the plurality of synchronized phasors.

45. The method of claim 24, further comprising removing implementation magnitude distortion from the sample frequency signal prior to forming each of the plurality of synchronized phasors.

46. The method of claim 45, further comprising removing implementation phase angle distortion from the sample frequency signal prior to forming each of the plurality of synchronized phasors.

47. The method of claim 24, wherein the power system signal comprises a local analog input signal.

48. The method of claim 24, wherein the power system signal comprises a digitized remote analog input signal.

49. The method of claim 24, wherein each of the plurality of synchronized phasors comprises a corresponding plurality of referenced phasor sequence quantities.

50. A method for estimating a plurality of synchronized phasors at predetermined times referenced to an absolute time standard in an electrical power system, the method comprising:

acquiring a power system signal

determining a frequency of the power system signal;

sampling the power system signal at a sampling interval rate based on a frequency of the power system signal to form a plurality of signal samples;

generating a plurality of acquisition time values based on an occurrence of each of the plurality signal samples at a corresponding plurality of different times referenced to the absolute time standard, each of the plurality of acquisition time values associated with a phasor magnitude and a phasor phase angle of each of the plurality of signal samples; and

for each of the plurality of signal samples, interpolating the phasor magnitude and rotating phasor phase angle to form a corresponding plurality of referenced phasor magnitudes and referenced phasor phase angles of the plurality of synchronized phasors based on a time difference between a corresponding selected acquisition time value of the plurality of acquisition time values and a predetermined time of the predetermined times referenced to the absolute time standard.

51. The method of claim 50, further comprising calculating the phasor magnitude and phasor phase angle of each of the plurality of signal samples at the plurality of acquisition time values prior to adjusting the phasor magnitude and the phasor phase angle of each of the plurality of signal samples to the corresponding plurality of referenced phasor magnitudes and referenced phasor phase angles.

52. The method of claim 50, wherein the rotating phasor phase angle comprises a rotation of 90 degrees.

53. The method of claim 50, further comprising the step of calculating an uncalibrated referenced phasor magnitude and a prealigned phasor phase angle of each of the plurality of signal samples at the plurality of acquisition time values prior to adjusting the phasor magnitude and the phasor phase angle to the corresponding plurality of referenced phasor magnitudes and referenced phasor phase angles.

54. The method of claim 50, wherein the time difference comprises a difference in time between an occurrence of a preceding selected acquisition time value of the plurality of acquisition time values and a predetermined time of the predetermined times referenced to the absolute time standard.

55. The method of claim 50, wherein the time difference comprises a difference in time between an occurrence of a predetermined time of the predetermined times referenced to the absolute time standard and a next selected acquisition time value of the plurality of acquisition time values.

56. The method of claim 50, wherein each of the plurality of synchronized phasors is further phase aligned to a reference phasor with predetermined phase and frequency.

57. The method of claim 56, wherein the predetermined frequency comprises 60 Hz.

58. The method of claim 56, wherein the predetermined frequency comprises 50 Hz.

59. The method of claim 50, wherein the absolute time standard is based on a global positioning system signal communicated via an IRIG timecode protocol.

60. The method of claim 50, wherein each of the plurality of synchronized phasors comprises a corresponding plurality of referenced phasor sequence quantities.

61. The method of claim 50, wherein the power system signal comprises a digitized remote analog input signal.

62. The method of claim 50, wherein the power system signal comprises a local analog input signal.