Differential protection method of long-distance ultra-high voltage direct-current (UHV DC) transmission line

Abstract

The present invention discloses a differential protection method of a long-distance ultra-high voltage direct-current (UHV DC) transmission line, and provides a method for properly compensating distributed capacitive current. Voltage current travelling waves are calculated according to line parameters and voltage current at two ends of a detected line, current travelling waves at two sides are compensated by using travelling wave propagation delays of a half of the line, and thus a positive travelling wave and a negative travelling wave of a middle point of the line are selected as calculating current of two sides of differential protection. When no faults exist inside the line or the middle point of the line fails, capacitive current can be fully compensated by the above method, and protection malfunction is prevented; and when positions beyond the middle point inside the line fail, the capacitive current can be partially compensated by the above method, and a ratio of acting current and braking current approximately equals to that when the capacitive current is fully compensated. With adoption of the method, the distributed capacitive current can be effectively compensated under various operating conditions, influences of the distributed capacitive current on DC differential protection can be greatly weakened, and the sensitivity and reliability of DC line protection are raised.

Description

technical field [0001] The invention relates to a differential protection method for a long-distance ultra-high voltage direct current transmission line, and proposes a direct current differential protection method based on distributed capacitance compensation, which belongs to the technical field of electric power system relay protection. Background technique [0002] HVDC transmission has more powerful and efficient power transmission capacity when the cross-section of the transmission line is the same, and has the advantages of large capacity, long distance, convenient grid interconnection, easy power adjustment, and narrow transmission corridor. Therefore, in long-distance, large-capacity It has obvious advantages in applications such as power transmission, asynchronous grid interconnection, new energy access to the grid, offshore platform power supply, and urban center area power supply. At present, my country's direct current transmission projects have been put into op...

AI Technical Summary

Problems solved by technology

According to the existing high-voltage DC line protection design requirements, the DC differential protection is responsible for cutting off high-resistance faults. It is a backup protection for DC transmission lines. It does not consider the capacitive current problem during the transient process of long-distance and large-capacity DC line faults, and the action speed is slow. poor protection

In the high-voltage DC lines currently in operation in my country, there have been many accidents where the faulty pole was blocked due to the pole-controlled low-voltage protection or the maximum trigger angle protection action. The line was forced to stop for a long time, causing serious economic losses

[0006] Traditional DC line differential protection does not consider the influence of transient capacitive current after long-distance and large-capacity DC line faults. Any transient process that causes DC voltage changes, such as out-of-area faults and start-up processes, can cause traditional DC differential protection to malfunction.

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