Method and apparatus for detecting vector shift

Patent metadata

Field	Value
Publication number	US-10041985-B2
Application number	US-201615097067-A
Country	US
Kind code	B2
Filing date	Apr 12, 2016
Priority date	May 13, 2015
Publication date	Aug 7, 2018
Grant date	Aug 7, 2018

Abstract

A method and an apparatus for detecting a vector shift in an AC power system, the apparatus comprising frequency measuring means adapted to determine a frequency of the AC power system, derivation means adapted to determine a time derivative of the frequency, filtering means adapted to filter the time derivative of the frequency, and detection means 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

The invention claimed is:

1. A method for detecting a vector shift in an AC power system, the method comprising:
a) measuring 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;
d) calculating time derivatives for filtered time derivatives of the frequency over a time period having the length of the fundamental period of the AC power system;
e) determining a number of positive time derivatives and a number of negative time derivatives obtained in step d);
f) detecting 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 obtained in step e) exceeding a predetermined threshold value; and
g) blocking 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.

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

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

4. The method of claim 1 , wherein the discrete Fourier transform is performed by using a fast Fourier transform.

5. The method of claim 1 , wherein in step e), 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 are taken into account.

6. A method for detecting a vector shift in an AC power system, the method comprising:
a) measuring 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;
d) calculating time derivatives for filtered time derivatives of the frequency over a first time period having the length of the fundamental period of the AC power system;
e) determining a number of positive time derivatives and a number of negative time derivatives obtained in step d);
f) if an absolute value of a difference between the number of positive time derivatives and the number of negative time derivatives obtained in step e) exceeds a predetermined threshold value, calculating 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;
g) determining a number of positive time derivatives and a number of negative time derivatives obtained in step f);
h) detecting 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 obtained in step g) exceeding the predetermined threshold value; and
i) blocking 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 method of claim 6 , wherein the moving window filter is a moving average filter or a moving median filter.

8. The method of claim 6 , wherein the fundamental period of the AC power system is 1/50 s or 1/60 s.

9. The method of claim 6 , wherein the discrete Fourier transform is performed by using a fast Fourier transform.

10. The method of claim 6 , wherein in steps e) and g), 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 are taken into account.

11. A method for detecting a vector shift in an AC power system, the method comprising:
a) measuring 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;
d) calculating time derivatives for filtered time derivatives of the frequency over a time period having the length of the fundamental period of the AC power system;
e) determining a number of positive time derivatives and a number of negative time derivatives obtained in step d);
f) detecting 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 obtained in step e) exceeding a predetermined threshold value; and
g) tripping a vector shift protection device of the AC power system in response to detecting the vector shift in the AC power system.

12. The method of claim 11 , wherein the moving window filter is a moving average filter or a moving median filter.

13. The method of claim 11 , wherein the fundamental period of the AC power system is 1/50 s or 1/60 s.

14. The method of claim 11 , wherein the discrete Fourier transform is performed by using a fast Fourier transform.

15. The method of claim 11 , wherein in step e), 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 are taken into account.

16. A method for detecting a vector shift in an AC power system, the method comprising:
a) measuring 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

Assignees

• Abb Technology Ag
• Abb Schweiz Ag

Inventors

• Suomi Frej

Classifications

• H02J13/36

  specially adapted for protection systems · CPC title

• H02J13/12

  Monitoring network conditions, e.g. electrical magnitudes or operational status · CPC title

• H02J3/388

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

• G01R23/02

  Arrangements for measuring frequency, e.g. pulse repetition rate; Arrangements for measuring period of current or voltage · CPC title

• G01R31/00 Primary

  Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere ({measuring superconductive properties G01R33/1238;} testing line transmission systems H04B3/46; testing or measuring semiconductors or solid state devices during manufacture {H10P74/00}) · CPC title