Grounding method of neutral point of medium-voltage system

Abstract

The invention provides a grounding method of a neutral point of a medium-voltage system, which is used for a medium-voltage transformer of a small resistance grounding system and is mainly used for atransformer of a star-connection system. The method comprises the following steps: comprehensively counting the length and the laying mode of the high-voltage cables in the factory, classifying the laying modes into overhead laid cables and non-overhead laid cables; calculating a cable distributed capacitance current, selecting a transformer that can run with a small resistance, configuring zero-sequence current protection for the transformer with possible small resistance grounding, and installing a neutral point grounding knife switch which can be remotely controlled at a neutral point of astation power transformer, which can reduce the operation overvoltage level, the fault current, the fault point current and the influence on other cable equipment, so that the problem of voltage risecaused by operation overvoltage is solved, the problem of overlarge current caused by single-phase grounding is alleviated, the problem of poor selectivity of zero-sequence protection after the medium-voltage system is grounded is solved, and the insulation design of the equipment can be designed according to the original design level without large investment.

Description

technical field [0001] The invention relates to the field of power generation optimization control, in particular to a grounding method for a neutral point of a medium-voltage system. Background technique [0002] In the power supply system of my country's medium-voltage power grid, most of them are small-current grounding systems (neutral point is not grounded or grounded through arc suppressing coil or grounded through resistance), and some areas or voltage levels (such as 20kV) adopt small resistance grounding. The small resistance grounding method is mainly in some developed countries represented by the United States. They have relatively high requirements on the overvoltage caused by the grounding arc. In some Southeast Asian countries, they imitate the technology of Britain and the United States, and one-sidedly adopt the small resistance grounding of the neutral point of the medium voltage system. It is required that the medium-voltage transformers in enterprises in the...

AI Technical Summary

Problems solved by technology

[0002] In the power supply system of my country's medium-voltage power grid, most of them are small-current grounding systems (neutral point is not grounded or grounded through arc suppressing coil or grounded through resistance), and some areas or voltage levels (such as 20kV) adopt small resistance grounding. The small resistance grounding method is mainly in some developed countries represented by the United States. They have relatively high requirements on the overvoltage caused by the grounding arc. In some Southeast Asian countries, they imitate the technology of Britain and the United States, and one-sidedly adopt the small resistance grounding of the neutral point of the medium voltage system. It is required that the medium-voltage transformers in enterprises in their countries adopt the method of neutral point small resistance grounding, which causes many faults to expand and the scope of power outages to increase, which brings great harm to production and safety.

[0003] In view of this situation, it is recommended to adopt the method of grounding the neutral point of individual medium-voltage transformers with small resistance to reduce the fault current caused by the single-phase ground fault, because the zero current flowing through the circuit breaker of the equipment that is single-phase grounded in the small resistance grounding system If the sequence current is very large, it will cause insufficient blocking capacity of the circuit breaker, causing the circuit breaker to explode. The huge fault current can throw the cable down the bridge frame tens of meters high, which will cause great damage to other cables around. Advantages of small resistance grounding: 1 1. Reduce the impact of operating overvoltage on the equipment and reduce the multiple of overvoltage; 2. The insulation level considered in equipment selection can be selected according to the phase voltage to reduce investment; 3. The zero-sequence protection sensitivity is relatively high, and the protection Convenient configuration; Disadvantages of the small resistance grounding system: 1. If the grounding current is large, the grounding must be tripped. If all medium-voltage transformers are grounded with small resistances, the protection selectivity is relatively poor and the power failure range is large; 2. The number of trips increases and is frequent The tripping increases and reduces the maintenance workload; 3. The interrupting capacity of the circuit breaker should be selected relatively large

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