Why are there so many vent plugs and gas guide pipes on a transformer? Why is oil injected from the bottom of the tank?

Vent plugs are commonly installed on the radiator, lifting platform, oil storage tank, and casing of transformers. This is because if vent plugs are not installed, air bubbles will be trapped at the top when oil is injected from the bottom of the tank, creating dead spots. These bubbles, if left inside the transformer, can easily lead to discharges. If they are trapped in the radiator, it can affect the oil flow and, consequently, the heat dissipation efficiency.

Due to the varying installation heights and structures of components like the radiator, lifting platform, and oil storage tank on transformers, having only one vent plug is insufficient to completely eliminate air bubbles. Therefore, it is typically required to have a separate vent plug for each component.

For casing with a voltage of 35kV and below, the internal oil is connected to the oil inside the tank. Thus, a vent plug is needed on the casing to ensure that the casing is filled with oil during the oil injection process. It is also required that the minimum oil level in the oil storage tank is higher than the oil level in the casing. For casing with a voltage of 60kV and above, the internal oil in the casing is generally not connected to the oil inside the tank. Consequently, there is no need for the oil storage tank to match the height of the casing.

To allow the gas in the lifting platform to be directed to the gas relay at any time during operation, gas guide pipes are welded on the edges of each lifting platform.

When injecting transformer oil into the tank at a high flow rate through the oil storage tank, static electricity can easily accumulate. This is particularly true when the transformer oil has high viscosity, contains small solid particles, or during dry winter conditions. Accumulated static electricity can lead to electrical sparks. Therefore, oil is generally not injected from the top; it is only done from the top during oil replenishment.

During bottom oil injection, the inlet pipe can be grounded to allow the oil to slowly rise based on its own pressure, avoiding the occurrence of static electricity sparks. It is recommended to open the vent plug to release gas when oil injection is nearing completion or after static discharge.

LuShan, est. 1975, is a Chinese professional manufacturer specializing in power transformers and reactors for 49 years. Leading products are single-phase transformer, three-phase transformers, DC inductors, AC reactors, filtering reactor, expoxy resin high-voltage transformer and intermediate, high-frequency products. Our transformers and reactors are widely used in 10 application areas: rapid transit, construction machinery, renewable energy, intelligent manufacturing, medical equipment, coal mine explosion prevention , excitation system, vacuum sintering, central air conditioning.

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