CN-121978453-A - Power distribution network fault direction discrimination method based on current distortion rate

CN121978453ACN 121978453 ACN121978453 ACN 121978453ACN-121978453-A

Abstract

The application belongs to the technical field of fault discrimination of a power distribution network containing distributed energy sources, and particularly relates to a fault direction discrimination method of the power distribution network based on a current distortion rate. The fault direction can be accurately identified, and protection misoperation caused by reverse current is avoided.

Inventors

MA LONG
LI LEI
JIANG WEINING
WANG YONG
WEN ZHICHAO
YOU YANG
YUAN TING
Cui Tianzhe
WANG YANG
GUO CHENGCHENG
LIU BIQING

Assignees

国网辽宁省电力有限公司盘锦供电公司

Dates

Publication Date: 20260505
Application Date: 20260114

Claims (7)

1. The utility model provides a distribution network fault direction discriminating method based on current distortion rate which is characterized in that the method comprises the following steps: Collecting three-phase current at the upstream line protection part of the distributed power supply; The distortion characteristics of the waveform are amplified by deriving the sampled three-phase current, and the total distortion rate of the current harmonic wave after derivation is calculated; and judging the fault direction according to the total distortion rate of the current harmonic waves.
2. The method for determining the fault direction of a power distribution network based on a current distortion rate according to claim 1, wherein the three-phase current is a three-phase fault current collected after a fault detected by a current protection element for a line protection place.
3. The method for discriminating a fault direction of a power distribution network based on a current distortion rate according to claim 1 wherein deriving an amplified waveform distortion characteristic for the sampled three-phase current includes: Calculating a first derivative of each phase of current; Calculating the amplitude values of the fundamental wave and each harmonic wave by adopting a fast Fourier transform method; and calculating the total distortion rate of the current harmonic according to the amplitude of each harmonic.
4. The method for distinguishing the fault direction of the power distribution network based on the current distortion rate according to claim 1, wherein the fault direction based on the current harmonic total distortion rate criterion comprises the following steps: When the current harmonic total distortion rate of any one phase of the three-phase fault current is detected to be below the current harmonic distortion rate threshold, the fault is located in the positive direction of the protection position.
5. The method for determining the fault direction of a power distribution network based on the current distortion rate according to claim 4, wherein the current harmonic distortion rate threshold is a current waveform distortion rate threshold measured at line protection by applying a three-phase short circuit fault to the end of the line.
6. The method for determining the fault direction of the power distribution network based on the current distortion rate according to claim 1, wherein a calculation formula of the total distortion rate of the current harmonics is as follows: , The total distortion rate of the current harmonic wave is; The calculated nth current harmonic amplitude for the fast fourier transform, Is the fundamental current amplitude.
7. The method for judging the fault direction of the power distribution network based on the current distortion rate according to claim 4, wherein when the fault is in the forward direction and the fault current exceeds the overcurrent protection threshold, the output of the AND gate through the overcurrent protection element at the protection position is 1, a delay tripping link is entered, and when the fault is in the reverse direction or the fault current does not exceed the overcurrent protection threshold, the output of the AND gate is 0, and the protection is blocked.

Description

Power distribution network fault direction discrimination method based on current distortion rate Technical Field The application belongs to the technical field of fault discrimination of a power distribution network containing distributed energy sources, and particularly relates to a power distribution network fault direction discrimination method based on a current distortion rate. Background Along with large-scale access of distributed power sources such as photovoltaic power and wind power, a single-power radial structure on which a traditional power distribution network depends for a long time is thoroughly broken, original unidirectional flowing tide distribution is converted into a complex network form supported by a multi-terminal power source, and the structural transformation directly causes significant variation of the magnitude, direction and continuous characteristic of fault current, so that the problems of malfunction, refusal and other protection failure frequently occur in the traditional overcurrent protection system, and the safe and stable operation of the power distribution network is seriously threatened. The fault characteristics of the distributed power supply connected to the power distribution network are greatly changed, so that the connection of the distributed power supply can have a certain influence on the direction elements protected in the power distribution network. In the traditional relay protection of a power distribution network, the current distortion rate is utilized to judge the direction of short-circuit current, and the principle is based on the characteristic change of current waveform and the output difference of different power supplies during faults. When the power distribution network works normally, the current waveform of the power distribution network is close to a sine wave and is regular in form, and after a fault occurs, the current waveform is distorted, and the distortion characteristics are closely related to the fault direction. Disclosure of Invention The technical problem to be solved by the application is to provide a power distribution network fault direction judging method based on current distortion rate, wherein the fault direction is distinguished by extracting the total distortion rate of the harmonic waves of fault current, namely the fault current waveform of a system power supply side is relatively smooth, the distortion rate is lower, the distributed power supply side is controlled by a non-linear converter, the harmonic wave content of the fault current is high, and the distortion rate is obviously higher. By setting a dynamic distortion rate threshold and combining an overcurrent protection criterion, a double locking logic of direction discrimination and overcurrent detection is formed, so that the fault direction can be accurately identified, and the protection misoperation caused by reverse current is avoided. The present application has been achieved in such a way that, A power distribution network fault direction distinguishing method based on current distortion rate comprises the following steps: Collecting three-phase current at the upstream line protection part of the distributed power supply; The distortion characteristics of the waveform are amplified by deriving the sampled three-phase current, and the total distortion rate of the current harmonic wave after derivation is calculated; and judging the fault direction according to the total distortion rate of the current harmonic waves. Further, the three-phase current is the three-phase fault current collected after the fault detected by the current protection element at the line protection position. Further, deriving the amplified waveform distortion characteristics for the sampled three-phase current includes: Calculating a first derivative of each phase of current; Calculating the amplitude values of the fundamental wave and each harmonic wave by adopting a fast Fourier transform method; and calculating the total distortion rate of the current harmonic according to the amplitude of each harmonic. Further, according to the direction of the current harmonic total distortion criterion fault, the method comprises the following steps: When the current harmonic total distortion rate of any one phase of the three-phase fault current is detected to be below the current harmonic distortion rate threshold, the fault is located in the positive direction of the protection position. Further, the current harmonic distortion rate threshold is a current waveform distortion rate threshold measured at line protection by applying a three-phase short circuit fault to the end of the line. Further, the calculation formula of the total distortion rate of the current harmonic wave is as follows:, The total distortion rate of the current harmonic wave is; the calculated nth current harmonic amplitude for the fast fourier transform (fast Fourier transform, FFT), Is the fundamental current amplitude