Main Power Transformer Neutral Point Gap Grounding

Knowledge of the neutral point discharge gap of the main power transformer

1. The discharge gap is mainly used to protect the arrester. When the lightning strike voltage exceeds the value that the arrester can protect, in order to prevent the arrester from being damaged by breakdown, a discharge gap is installed. When there is a high lightning strike voltage, the gap is broken down and discharged, thus protecting the arrester. As for how to cooperate with each other , depends on the lightning protection voltage of the arrester.

2. Prevent dangerous overvoltage at the neutral point of the high-voltage side fault after the grounding change trips.

3. The gap protection of the neutral point of the system of 110KV and above is mainly to prevent overvoltage! Because the equipment at this voltage level adopts graded insulation due to the problem of insulation investment, the insulation level is relatively low near the neutral point. If overvoltage occurs, it will cause equipment damage, and the gap protection can play a role, but due to the selection of neutral point grounding, a system should not have too many neutral points grounding, so some main power transformers have neutral point grounding switches. Not closed (configuration reason for protection). At this time, if overvoltage occurs due to the transformer itself, the transformer will be protected by the gap protection. The principle is the voltage breakdown. Under a certain voltage, the gap will break down, leading the voltage to the ground.

Gap protection can play the role of main power transformer winding insulation. When the system has overvoltage (atmospheric overvoltage, operating overvoltage, resonance overvoltage, lightning strike overvoltage, etc.), the zero-sequence protection acts when the gap is broken down, and the gap is not There is an overvoltage protection action to cut off the transformer during breakdown.

4. Meet the sensitivity requirements of protection.

5. Prevent overvoltage caused by different closing periods and damage to insulation.

Definition of the so-called guard gap:

It is a simple lightning protection device composed of two metal electrodes. One of the electrodes is fixed on the insulator and connected to the live wire, the other electrode is connected to the grounding device through the auxiliary gap, and the specified gap distance is maintained between the two electrodes. Under normal circumstances, the protective gap is insulated from the ground, and the dielectric strength is lower than the insulation level of the protected line. Therefore, when the line is struck by lightning, the protective gap is first broken down due to overvoltage, and a large amount of lightning current is released. into the earth, the overvoltage will be greatly reduced, so as to protect the circuit and electrical equipment.