A Line Current Differential Protection Method against Effects of Transition Resistance and Load Current

Abstract

The invention discloses a line current differential protection method capable of preventing influences of both transitional resistance and load current. According to the method, the differential current is calculated by utilizing current on two sides of a transmission line; the protection criterion molecular calculated value is obtained through phase of the current of the transmission line and the differential current; the minimum value of the three-phase current is multiplied by the difference value of the differential current and the current on the two sides to obtain the protection criterion denominator calculated value; and then whether the current differential protection sends out an action trip signal is determined by whether the ratio of the protection criterion molecular calculated value and the protection criterion denominator calculated value is larger than the setting coefficient. The method provided by the invention can achieve reliable braking in case of an external failure of the transmission line, has very high action sensitivity in case of an internal failure of the transmission line, and can act sensitively and reliably when the transmission line falls into a single-phase high-resistance ground fault, and the action performance is free from the influences of both load current and transitional resistance.

Description

technical field [0001] The invention relates to the technical field of electric power system relay protection, in particular to a line current differential protection method against the influence of transition resistance and load current. Background technique [0002] Because it is not affected by the power system operation mode and grid structure and has a natural phase selection function, the current differential protection has always been the main protection of various voltage levels of transmission lines. In the 220kV and below voltage level transmission lines, because the distributed capacitance current along the transmission line is very small, the distributed capacitance has little influence on the operation performance of the current differential protection. However, the voltage and current transmission of EHV / UHV AC transmission lines has an obvious wave process, and the distributed capacitance current along the line is very large. The protection is faced with a la...

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Problems solved by technology

However, the voltage and current transmission of EHV / UHV AC transmission lines has an obvious wave process, and the distributed capacitance current along the line is very large. The protection is faced with the large starting current of current differential protection, and in order to prevent the protection from malfunctioning, increasing the setting value of the starting current of the protection will lead to insufficient sensitivity of the protection action

Especially when a single-phase high-resistance grounding fault occurs on the transmission line, the fault current is very small, and the fault current may even be smaller than the load current. The dynamic protection will refuse to operate, and the faulty line cannot be isolated from the grid in time, which will bring huge security risks to the stability of the power system

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