How to conduct a pump test for oil-immersed transformers?

Performing a pump test for oil-immersed transformers is an essential step in the production and maintenance processes. For transformers that have completed the assembly, especially those with a capacity of 8000kVA, voltage of 35kV and below, and equipped with an oil storage tank, a pump test must be carried out, as shown in Figure 87-1(a). For transformers with a capacity of 3150kVA, voltage of 60kV and above, the same method can be employed even after oil filling to ensure the quality during transportation and storage. During the pump test, the pump joint should be installed at the plug seat on top of the oil storage tank or at the dismantled box top flange, and the oil level position on the oil gauge should be recorded.

The procedure is as follows: Hold the windpipe with the left hand towards the pump nozzle and introduce dry compressed air; with the right hand, tighten the pressure gauge from the upper end of the pump joint, forcing a gap (i.e., opening the sealing surface) between the joint and the internal components, allowing gas to enter the pressure gauge and the inside of the oil storage tank. As the gas is injected into the tank, the oil level on the oil gauge will slowly decrease. When it drops to approximately 30-40mm, and the pressure gauge shows a pressure of 0.045MPa, rotate the pressure gauge upward to seal the internal components with the joint, completing the gas injection.

During the pump test, if there is a leakage of gas in the transformer, it can be observed from the oil gauge that the oil gradually returns to its position before the pump; if there is a oil leakage, the oil level will drop even lower. Within 8 hours after the pump test, the operator needs to repair the leaking oil and gas areas, and then apply pressure for an additional 4 hours (2 hours for dismantled products). Only when the pressure is not less than 0.02MPa and there is no leaking oil, the pump test is considered qualified.

When withdrawing the pump, the operator should use the left hand to block the valve, unscrew the sealing surface of the pressure gauge, and check that the residual pressure is not less than 0.02MPa. For the pump test method of single-casing transformers at 60kV and 110kV, refer to Figure 87-2, where the pump joint is connected to the pressure gauge, and a bicycle valve is welded to the joint for inflation using compressed air or an inflation tube.

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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