CN-115811031-B - Single-ended MMC direct-current power distribution network monopole grounding protection method based on classification similarity analysis

CN115811031BCN 115811031 BCN115811031 BCN 115811031BCN-115811031-B

Abstract

The invention discloses a single-ended MMC direct-current distribution network monopole grounding protection method based on classification similarity analysis, which mainly comprises the following steps of judging whether monopole grounding faults occur by monitoring changes of positive and negative voltages of a direct-current distribution network, judging a fault pole according to positive and negative voltage change characteristics when the monopole grounding faults occur, if only one of positive and negative similarity coefficients of all feeder lines is negative, calculating sum of similarity coefficients of fault pole currents of all feeder lines, if only one of positive and negative similarity coefficients of two or more feeder lines is negative, then the feeder line is the fault feeder line, otherwise, calculating sum of similarity coefficients of current sampling values corresponding to all feeder lines based on positive and negative poles, and the feeder line corresponding to the minimum value is the fault feeder line. The method can accurately judge the feeder line, has the characteristics of simple calculation, high accuracy and easy realization, and can effectively improve the operation and maintenance efficiency, reduce the power failure range and improve the operation reliability of the direct current distribution network.

Inventors

ZHANG WEI
JIANG HUA
GUO YIN
LIU YANG
LI LEI
SHEN XINGLAI
BAI YUDONG
LIU NING

Assignees

国网江苏省电力有限公司徐州供电分公司

Dates

Publication Date: 20260505
Application Date: 20210914

Claims (5)

1. A single-ended MMC direct-current distribution network monopole grounding protection method based on classification similarity analysis is characterized by comprising the following steps: s1, numbering all feeder lines of a single-ended direct current power distribution network; S2, specifying a current direction according to the flow direction of the bus and the line; S3, judging whether the installation of the transformer is correct or not by monitoring the current direction of each line when the direct-current power distribution network normally operates; S4, determining the transformation ratio n of each current transformer; S5, synchronously sampling the voltage to the ground of the positive electrode and the negative electrode interelectrode voltage and positive and negative current of each feeder line; s6, determining whether a monopole ground fault occurs or not according to the change of the voltages of the positive electrode and the negative electrode to the ground; S7, judging a fault pole according to the magnitude of the voltage of the positive electrode and the negative electrode to the ground when a monopole ground fault occurs; s8, determining the data length N of a current criterion through the change characteristic of the fault pole voltage; S9, calculating similarity coefficients p i of positive and negative currents of each feeder line by using positive and negative current sampling values of each feeder line, wherein when all the p i are negative, the feeder line is a fault feeder line, fault line selection is finished, a related protection function is executed, otherwise, the step (10) is continued; S10, calculating the sum P ∑i of the similarity coefficients of the fault pole currents of all the feeder lines based on the fault pole currents and all other feeder line fault pole currents by using the fault pole current sampling values of all the feeder lines, wherein when only one P ∑i is negative, the feeder line is the fault feeder line, fault line selection is finished, and a related protection function is executed, otherwise, the step (11) is carried out; S11, calculating the sum P ' ∑i of the similarity coefficient of each feeder line based on the positive and negative current sampling values and the sum of the positive and negative current sampling values of other all feeder lines by utilizing the positive and negative current sampling values of each feeder line, finding out the minimum value P ' ∑i·min from all feeder lines, wherein the feeder line corresponding to P ' ∑i·min is a fault feeder line, and executing the related protection function after the fault line selection is finished.
2. The single-ended MMC direct current distribution network monopole grounding protection method based on classification similarity analysis according to claim 1, wherein the specified current flows from a bus to a line to be positive, and flows from the line to the bus to be negative.
3. The single-ended MMC direct-current distribution network monopole grounding protection method based on classification similarity analysis according to claim 1, wherein in step S9, positive and negative current sampling values of all feeder lines are utilized, similarity coefficients p i of positive and negative currents of all feeder lines are calculated according to formula (3), when all only one p i is negative, the feeder line is a fault feeder line, fault line selection is finished, relevant protection functions are executed, otherwise, step (10) is continued; wherein i i+ (k)、i i- (k) is the kth sampling value of the positive and negative electrode currents of the ith feeder line respectively.
4. The single-ended MMC direct-current distribution network monopole grounding protection method based on classification similarity analysis according to claim 1, wherein in step S10, the sum P ∑i of the similarity coefficients of each feeder line based on fault pole current and all other feeder line fault pole currents is calculated according to formula (4) by utilizing each feeder line fault pole current sampling value, when only one P ∑i is negative, the feeder line is the fault feeder line, the fault line selection is finished, the relevant protection function is executed, otherwise, step (11) is executed; Wherein p i·s is the cross correlation coefficient of the fault pole current of the ith feeder line and the ith feeder line, i i·g (k) is the kth sampling value of the fault pole current of the ith feeder line, and n i 、n s is the transformation ratio of the current transformers of the ith feeder line and the ith feeder line respectively.
5. The single-ended MMC direct-current distribution network monopole grounding protection method based on classification similarity analysis of claim 1 is characterized in that in the step S11, positive and negative current sampling values of all feeder lines are utilized, the sum P ' ∑i of each feeder line based on the positive and negative current sampling values and the mutual similarity coefficients of the positive and negative current sampling values and the other positive and negative current sampling values of all feeder lines is calculated according to a formula (5), the minimum value P ' ∑i·min is found out from all feeder lines, the feeder line corresponding to P ' ∑i·min is a fault feeder line, fault line selection is finished, and relevant protection functions are executed; Wherein p' i·s is the cross correlation coefficient of the sum of the positive and negative currents of the ith feeder line and the ith feeder line, i i·p (k) is the kth sampling value of the positive current of the ith feeder line, and i i·N (k) is the kth sampling value of the negative current of the ith feeder line.

Description

Single-ended MMC direct-current power distribution network monopole grounding protection method based on classification similarity analysis Technical Field The invention belongs to the field of power system relay protection, and particularly relates to a single-ended MMC direct-current power distribution network monopole grounding protection method based on classification similarity analysis. The background technology is as follows: When the direct current side of the direct current distribution network is sampled by the clamping resistor in a grounding mode, the direct current side has the characteristics of small fault current and basically unchanged interelectrode voltage when a monopole grounding fault occurs, so that the direct current distribution network is widely applied to the direct current distribution network, particularly an alternating current non-grounding distribution network, when the monopole grounding fault occurs, the fault characteristic is not obvious, the resistance change range of the fault point is large, and the monopole grounding fault protection is always a difficult point of relay protection. Because the fault characteristics are complex when the direct-current distribution network has a single-pole ground fault, the fault types are more, and the fault components are relatively small, so that the accuracy of the single-pole ground fault protection is seriously affected. However, at present, the protection of the direct-current power distribution network is still in a theoretical research stage, and factors such as imperfection of direct-current protection equipment all cause great restriction and challenges to the protection of the direct-current power distribution network, so that the research on the single-pole grounding protection method of the direct-current power distribution network meeting the accuracy is a technical problem to be solved in the construction of the direct-current power distribution network. Disclosure of Invention In order to solve the technical problems of the background technology, the invention provides a single-ended MMC direct-current distribution network monopole grounding protection method based on classification similarity analysis, which can accurately realize the protection of monopole grounding faults according to the fault characteristics of capacitance current similarity of each interval when the monopole grounding faults occur in the direct-current distribution network and alarm or trip according to requirements. In order to achieve the technical purpose, the technical scheme of the invention is as follows: a single-ended MMC direct current power distribution network monopole grounding protection method based on classification similarity analysis comprises the following steps: s1, numbering all feeder lines of a single-ended direct current power distribution network; S2, specifying a current direction according to the flow direction of the bus and the line; S3, judging whether the installation of the transformer is correct or not by monitoring the current direction of each line when the direct-current power distribution network normally operates; S4, determining the transformation ratio n of each current transformer; S5, synchronously sampling the voltage to the ground of the positive electrode and the negative electrode interelectrode voltage and positive and negative current of each feeder line; s6, determining whether a monopole ground fault occurs or not according to the change of the voltages of the positive electrode and the negative electrode to the ground; S7, judging a fault pole according to the magnitude of the voltage of the positive electrode and the negative electrode to the ground when a monopole ground fault occurs; s8, determining the data length N of a current criterion through the change characteristic of the fault pole voltage; S9, calculating similarity coefficients p i of positive and negative currents of each feeder line by using positive and negative current sampling values of each feeder line, wherein when all the p i are negative, the feeder line is a fault feeder line, fault line selection is finished, a related protection function is executed, otherwise, the step (10) is continued; S10, calculating the sum P ∑i of the similarity coefficients of the fault pole currents of all the feeder lines based on the fault pole currents and all other feeder line fault pole currents by using the fault pole current sampling values of all the feeder lines, wherein when only one P ∑i is negative, the feeder line is the fault feeder line, fault line selection is finished, and a related protection function is executed, otherwise, the step (11) is carried out; S11, calculating the sum P ' ∑i of the similarity coefficient of each feeder line based on the positive and negative current sampling values and the sum of the positive and negative current sampling values of other all feeder lines by utilizing the positive and negative current