Advantages of neutral point grounding system through arc suppression coil

In the power system, whether the neutral point of the generator and transformer is grounded or not involves multiple aspects such as technology, economy, and safety, and is a comprehensive issue. The neutral point is grounded through an arc suppression coil (also known as ineffective grounding). According to the current when a single-phase grounding fault occurs in the system, my country divides it into a small grounding current system. According to relevant regulations in my country, in a 3-10kV power system, if the capacitive current exceeds 30A when the single-phase is grounded; or the capacitive current exceeds 10A when the single-phase is grounded in a 35-60kV power system, the neutral point of the system should adopt an arc suppression coil grounding method.

Arc suppression coils have been used for more than 80 years. The operating experience of medium-voltage power systems shows that the neutral point grounding method through arc suppression coils has significant advantages.

1. Improve the power supply reliability of the power system

First, the system does not cut off power when a single-phase grounding fault occurs. The arc suppression coil is an adjustable inductance coil with an iron core. When a single-phase grounding fault occurs in the power grid due to any reason such as poor insulation of electrical equipment, external force damage, operator misoperation, internal overvoltage, etc., the grounding current passes through the arc suppression coil in the form of an inductive current, which is opposite to the direction of the capacitive current. It can make the current at the grounding point very small or equal to zero, thereby eliminating the arc at the grounding point and the various hazards caused by it, automatically eliminating the fault, and will not cause the relay protection and circuit breaker to operate, greatly improving the power supply reliability of the power system.

2 Not passive in case of permanent ground fault

Since the arc suppression coil can effectively limit the single-phase ground fault current, although the voltage of the non-fault phase increases by three times, the line voltage between the three-phase conductors is still balanced, the generator can be exempted from asymmetric loads, and the power system can continue to operate. Especially when the power supply is tight or the consequences of power outage are serious, there is enough time to start the backup power supply or transfer the load to avoid a sudden interruption of power supply to users and fall into a passive situation.

3. Protective effect on the power equipment of the whole network

When a single-phase grounding fault occurs in a neutral point grounding system through an arc suppression coil, the grounding current has nothing to do with the location of the fault point. Since the residual current is very small, the grounding arc can be extinguished instantly, which effectively limits the harmful effects of arc overvoltage. Relay protection and automatic devices, lightning arresters, lightning rods, etc. can only protect specific equipment, factories and lines, but arc suppression coils can prevent most single-phase grounding faults from developing into phase-to-phase short circuits. Generators can be exempted from supplying short-circuit currents, transformers and other equipment can be protected from the impact of short-circuit currents, and relay protection and automatic devices do not need to be operated, and circuit breakers do not need to be operated, thereby protecting all power equipment in the system.

4. Good electromagnetic compatibility

In today's society, various information processing systems are widely used in national defense, social production, and all aspects of life, but their anti-interference ability is very poor, and electromagnetic compatibility issues have become a new research field. Strong electricity interferes with weak electricity, and the power system is the main aspect of the contradiction. At present, the best solution is to introduce optical fiber, but there is an increase in investment. In fact, since the neutral point arc suppression coil grounding system effectively limits the single-phase grounding fault current, it is an economical and effective method. The compensation system can provide a good electromagnetic compatibility environment for the communication system.