Fast power swing unblocking method and apparatus for distance protection in power system

Patent metadata

Field	Value
Publication number	US-9496706-B2
Application number	US-200813002701-A
Country	US
Kind code	B2
Filing date	Jul 7, 2008
Priority date	Jul 7, 2008
Publication date	Nov 15, 2016
Grant date	Nov 15, 2016

Abstract

The present invention discloses a fast power swing unblocking method and apparatus for a distance protection in a power system, which is able to ensure fast phase-segregated tripping of distance protection for faults during a power swing (3-phase or 2-phase swing). The power swing unblocking method in a power system according to the present invention comprises calculating changing rates of impedances for all operating loops of the distance protection in the power system; and determining a fault loop based on the calculated changing rates. If there is a fault loop, a blocked distance zone for the fault loop is unblocked. Before calculating the changing rates, whether the power system is under a power swing is checked and a distance zone that might mal-operate under the power swing is blocked if it is checked that the power system is under the power swing. By applying this invention, the performance of the distance protection during power swings can be improved, and the distance protection can ensure faster and phase-segregated operation, which are very beneficial for the system reliability.

First claim

What is claimed is:

1. A power swing unblocking method in a power system comprising:
checking whether the power system is under a power swing;
blocking a distance zone that might mal-operate under the power swing in response to determining the checked power system is under the power swing
measuring impedances for all operating loops in the power system;
calculating changing rates of the impedances for all of the operating loops in the power system;
determining one or more fault loops based on the calculated changing rates;
and
unblocking a blocked distance zone for a fault loop;
wherein during a 3-phase power swing, in the step of determining the fault loop based on the calculated changing rates, if the changing rates of all the operating loops continue being smaller than those of a predetermined period before a set period respectively and the changing rates of all the operating loops are close to each other, a symmetrical fault is determined.

2. The method according to claim 1 , further comprising:
unblocking the blocked distance zone for the fault loop within 120 ms of said fault.

3. The method according to claim 1 , wherein,
the changing rates of the impedances for all the operating loops in the power system are respectively calculated according to the following formula:
D y ( x )=abs( Z y ( x )− Z y ( x−p ))

where D is the changing rate, subscript “y” represents the operating loop under measurement, Z is a measured impedance, x is a current measured sample point and p represents a number of sample points during an intervening period.

4. The method according to claim 1 , wherein during a 3-phase power swing, in the step of determining the fault loop based on the calculated changing rates, if the changing rate of one phase-ground loop continues being smaller than those of the other two phase-ground loops for a set period, the one phase-ground loop is determined as the fault loop.

5. The method according to claim 1 , wherein during a 3-phase power swing, in the step of determining the fault loop based on the calculated changing rates, if the changing rate of one phase-to-phase loop continues being smaller than those of the other two phase-to-phase loops for a set period, the one phase-to-phase loop is determined as the fault loop.

6. The method according to claim 1 , wherein during a 2-phase power swing, in the step of determining the fault loop based on the calculated changing rates, if the changing rates of all the 3 operating loops continue being smaller than those of predetermined period before for a set period respectively and the changing rates of all the operating loops are close to each other, a 2-phase-to-ground fault is determined.

7. The method according to claim 1 , wherein during a 2-phase power swing, in the step of determining the fault loop based on the calculated changing rates, if the changing rate of one operating loop continues being smaller than those of the other two operating loops for a set period, the one operating loop is determined as the fault loop.

8. The method according to claim 1 , wherein in the step of determining the fault loop based on the calculated changing rates, the operating loop with a smallest changing rate is determined as the fault loop.

9. A power swing unblocking apparatus in a power system comprising:
a checking means configured to check whether the power system is under a power swing;
a blocking means configured to block one or more distance zones that might mal-operate under the power swing in response to the power system under the power swing,
a measuring means configured to measure impedances for all operating loops in the power system;
a central processing unit configured to calculate changing rates of the impedances for all of the operating loops in the power system;
a determining means configured to determine one or more fault loops based on the changing rates calculated by the calculating means;
and
unblocking means configured to unblock a blocked distance zone for the fault loop;
wherein the determining means is further configured to during a 3-phase power swing, if the changing rates of all the operating loops continue being smaller than those of a predetermined period before a set period respectively and the changing rates of all the operating loops are close to each other, a symmetrical fault is determined.

10. The apparatus according to claim 9 , wherein the unblocking means unblocks the blocked distance zone for the fault loop within 120 ms of said fault.

11. The apparatus according to claim 9 , wherein
the changing rates of the impedances for all the operating loops in the power system are respectively calculated by the calculating means according to the following formula:
D y ( x )=abs( Z y ( x )− Z y ( x−p ))

where D is the changing rate, a subscript “y” represents the operating loop under measurement, Z is a measured impedance, x is a current measured sample point and p represents a number of sample points during an intervening period.

12. A computer readable storage medium encoded with computer readable instructions, which, when executed by a processor, cause the processor to:
check whether the power system is under a power swing;
block a distance zone that might mal-operate under the power swing in response to determining the checked power system is under the power swing;
measure impedances for all operating loops in the power system;
calculate changing rates of impedances for all of the operating loops in a power system;
determine one or more fault loops based on the calculated changing rates;
and
unblock a blocked distance zone for a fault loop;
wherein during a 3-phase power swing, in the step of determining the fault loop based on the calculated changing rates, if the changing rates of all the operating loops continue being smaller than those of a predetermined period before a set period respectively and the changing rates of all the operating loops are close to each other, a symmetrical fault is determined.

13. The computer readable storage medium of claim 12 , the computer readable instructions, when executed by the processor, further cause the processor to unblock the blocked distance zone for the fault loop in less than 120 ms after said fault.

14. The computer readable storage medium of claim 12 , wherein the changing rates of the impedances for all the operating loops in the power system are respectively calculated according to the following formula:
D y ( x )=abs( Z y ( x )− Z y ( x−p ))

where D is the changing rate, subscript “y” represents the operating loop under measurement, Z is a measured impedance, x is a current measured sample point and p represents a number of sample points during an intervening period.

15. The computer readable storage medium of claim 12 , wherein during a 3-phase power swing, when determining the fault loop based on the calculated changing rates, at least one of:
if the changing rates of all the operating loops continue being smaller than those of a predetermined period before for a set period respectively and the changing rates of all the operating loops are close to each other, a symmetrical fault is determined;
if the changing rate of one phase-ground loop continues being smaller than those of the other two phase-ground loops for a set period, the one phase-ground loop is determined as the fault loop; or
if the changing rate of one phase-to-phase loop continues being smaller than those of the other two phase-to-phase loops for a set period, the one phase-to-phase loop is determined as the fault loop.

16. T

Assignees

• Su Bin
• Jing Lei
• Liu Qianjin
• Abb Research Ltd

Inventors

• Su Bin
• Jing Lei
• Liu Qianjin

Classifications

• G01R31/088

  Aspects of digital computing · CPC title

• G01R31/085

  in power transmission or distribution lines, e.g. overhead · CPC title

• H02H3/40 Primary

  responsive to ratio of voltage and current · CPC title