Method and apparatus for detecting vector shift

Patent metadata

Field	Value
Publication number	US-2016334446-A1
Application number	US-201615097067-A
Country	US
Kind code	A1
Filing date	Apr 12, 2016
Priority date	May 13, 2015
Publication date	Nov 17, 2016
Grant date	—

Abstract

A method and an apparatus for detecting a vector shift in an AC power system, the apparatus comprising frequency measuring means ( 10 ) adapted to determine a frequency of the AC power system, derivation means ( 20 ) adapted to determine a time derivative of the frequency, filtering means ( 30 ) adapted to filter the time derivative of the frequency, and detection means ( 40, 50, 60, 70 ) adapted to calculate time derivatives for the filtered time derivatives of the frequency over a time period having the length of the fundamental period of the AC power system, to determine a number of positive and negative time derivatives among the calculated time derivatives, and to detect a vector shift in the AC power system in response to an absolute value of a difference between the determined number of positive time derivatives and negative time derivatives exceeding a predetermined threshold value.

First claim

1 . An apparatus comprising:
frequency measuring circuitry structured to determine a frequency of an AC power system on the basis of a difference between a first phase angle of a voltage of the AC power system and a second phase angle of the voltage of the AC power system, the first and second phase angles corresponding to time points spaced by a fundamental period of the AC power system, wherein the frequency measuring circuitry is adapted to determine the first and second phase angles of the voltage of the AC power system using the discrete Fourier transform of the sliding window type, which has a length corresponding to the fundamental period of the AC power system; derivation circuitry structured to determine a time derivative of the frequency; filtering circuitry structured to filter the time derivative of the frequency with a moving window filter, wherein a window of the moving window filter has the length of the fundamental period of the AC power system; and either detection circuitry structured to: calculate time derivatives for the filtered time derivatives of the frequency over a time period having the length of the fundamental period of the AC power system; determine a number of positive time derivatives and a number of negative time derivatives among the calculated time derivatives; and detect a vector shift in the AC power system in response to an absolute value of a difference between the determined number of positive time derivatives and the determined number of negative time derivatives exceeding a predetermined threshold value, or detection circuitry structured to: calculate time derivatives for the filtered time derivatives of the frequency over a first time period having the length of the fundamental period of the AC power system; determine a number of positive time derivatives and a number of negative time derivatives among the time derivatives calculated over the first time period; calculate, if an absolute value of a difference between the determined number of positive time derivatives and the determined number of negative time derivatives exceeds a predetermined threshold value, time derivatives for the filtered time derivatives of the frequency over a second time period immediately following the first time period and having the length of the fundamental period of the AC power system; determine a number of positive time derivatives and a number of negative time derivatives among the time derivatives calculated over the second time period; and detect a vector shift in the AC power system in response to an absolute value of a difference between the number of positive time derivatives and the number of negative time derivatives among the time derivatives calculated over the second time period exceeding the predetermined threshold value.

2 . The apparatus of claim 1 , wherein the moving window filter is a moving average filter or a moving median filter.

3 . The apparatus of claim 1 , wherein the fundamental period of the AC power system is 1/50 s or 1/60 s.

4 . The apparatus of claim 1 , wherein the frequency measuring circuitry is adapted to perform the discrete Fourier transform by using a fast Fourier transform.

5 . The apparatus of claim 1 , wherein the detection circuitry is adapted to take into account only time derivatives having a magnitude greater than a predetermined lower magnitude threshold and/or time derivatives having a magnitude smaller than a predetermined upper magnitude threshold when determining the number of positive time derivatives and the number of negative time derivatives.

6 . The apparatus of claim 1 , comprising: blocking circuitry structured to block a tripping of a frequency protection of the AC power system for a predetermined time period in response to detecting the vector shift in the AC power system.

7 . The apparatus of claim 1 , wherein the apparatus is a frequency protection device for an AC power system or a vector shift protection device for an AC power system.

8 . A device for detecting a vector shift in an AC power system, the device comprising a processor and a memory storing instructions that, when executed by the processor, cause the device to:
measure a frequency of the AC power system on the basis of a difference between a first phase angle of a voltage of the AC power system and a second phase angle of the voltage of the AC power system, the first and second phase angles corresponding to time points spaced by a fundamental period of the AC power system, wherein the first and second phase angles of the voltage of the AC power system are determined by using the discrete Fourier transform of the sliding window type, which has a length corresponding to the fundamental period of the AC power system; determine a time derivative of the frequency; filter the time derivative of the frequency with a moving window filter, wherein a window of the moving window filter has the length of the fundamental period of the AC power system; and either calculate time derivatives for the filtered time derivatives of the frequency over a time period having the length of the fundamental period of the AC power system; determine a number of positive time derivatives and a number of negative time derivatives among the calculated time derivatives; and detect a vector shift in the AC power system in response to an absolute value of a difference between the determined number of positive time derivatives and the determined number of negative time derivatives exceeding a predetermined threshold value, or calculate time derivatives for the filtered time derivatives of the frequency over a first time period having the length of the fundamental period of the AC power system; determine a number of positive time derivatives and a number of negative time derivatives among the time derivatives calculated over the first time period; calculate, if an absolute value of a difference between the determined number of positive time derivatives and the determined number of negative time derivatives exceeds a predetermined threshold value, time derivatives for the filtered time derivatives of the frequency over a second time period immediately following the first time period and having the length of the fundamental period of the AC power system; determine a number of positive time derivatives and a number of negative time derivatives among the time derivatives calculated over the second time period; and detect a vector shift in the AC power system in response to an absolute value of a difference between the number of positive time derivatives and the number of negative time derivatives among the time derivatives calculated over the second time period exceeding the predetermined threshold value.

9 . A method for detecting a vector shift in an AC power system, the method comprising:
a) determining a frequency of the AC power system on the basis of a difference between a first phase angle of a voltage of the AC power system and a second phase angle of the voltage of the AC power system, the first and second phase angles corresponding to time points spaced by a fundamental period of the AC power system, wherein the first and second phase angles of the voltage of the AC power system are determined by using the discrete Fourier transform of the sliding window type, which has a length corresponding to the fundamental period of the AC power system; b) determining a time derivative of the frequency; c) filtering the time derivative of the frequency with a moving window filter, wherein a window of the moving window filter has the length of the fundamental period of the AC power system; and either d) calculating time derivatives for the filtered time derivatives of the frequency over a time period h

Assignees

• Abb Technology Ag

Inventors

• Suomi Frej

Classifications

• H02J13/36

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• H02J13/12

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• H02J3/388

  Arrangements for the handling of islanding, e.g. for disconnection or for avoiding the disconnection of power · CPC title

• H02H3/353

  involving comparison of phase voltages · CPC title

• G01R19/2513

  Arrangements for monitoring electric power systems, e.g. power lines or loads; Logging · CPC title