How to Prevent Water and Air From Entering the Power Transformer?

The power transformer must be well sealed during transportation and storage.

After the inflatable power transformer is transported to the site, a pressure gauge should be installed before installation to closely monitor the gas pressure.

When the pressure is too low, add dry gas.

Power transformers that have been placed on-site for more than 6 months should be filled with oil for storage and fitted with oil pillows and capsules to prevent ingress of water and moisture.

Before filling the oil, the pressure of the sealing gas must be measured, the sealing condition must be checked, and the dew point should be measured if necessary.

In order to prevent the power transformer from entering water and damp during installation and operation, the general cap on the top of the bushing, the top of the oil conservator, the riser of the bushing, and its connecting pipe must be well sealed.

If necessary, a leak detection test should be carried out.

If the insulation has been found to be damp, corresponding measures should be taken in time.

How to ground the pad-mounted substation

For coolers with extended structure, metal bellows should be used to connect the cooler and the box.

Water cooling is generally not used for power transformers in new or expanded projects. If water cooling is necessary for special occasions, a double-layer copper pipe cooling system should be used.

For in-service water-cooled power transformers, the water cooler and submersible pump should be tested for leaks one by one in accordance with the installation instructions of the manufacturer before installation, and disassembled for inspection if necessary.

The water cooler in operation must ensure that the oil pressure is greater than the water pressure.

The oil inlet valve of the submersible pump should be opened, and the oil outlet valve should be used to adjust the oil flow.

Monitor the indications of the differential pressure relay and pressure gauge regularly during operation.

Each water cooler should be equipped with a water drain valve, and check whether there are any oil splashes in the water. In winter, the cooler should be prevented from freezing and cracking if it is not in operation. Combine major and minor repairs to check the oil pipe of the cooler for leaks.


Before the power transformer is put into operation, the residual gas in the casing riser, the dead zone in the oil pipeline, and the top of the cooler must be removed many times.

Before the power transformer with strong oil circulation is put into operation, all cooling equipment should be started to circulate the oil, and the pump can be operated with electricity after stopping the pump to remove residual gas.

After replacing or overhauling various types of coolers, do not directly put the newly installed and overhauled coolers into the power transformer when the power transformer is energized to prevent air remaining in the cooler or oil pipeline from entering the power transformer during installation and maintenance.

The newly installed or overhauled power transformer should be vacuum treated and oiled according to the manufacturer’s instructions, and its vacuum degree, vacuum time, oil feed rate, etc. should meet the requirements.

The oil tank equipped with the load-regulating switch should be vacuumed at the same time, and reach the same vacuum degree as the oil tank of the power transformer body at the same time, so as to avoid oil leakage of the switch oil tank.

IEC 60076 -24:2020: Specification of voltage regulating power transformers

Prevention of insulation breakdown accidents of power transformers

The oil conservator equipped with a sewage valve should be combined with minor repairs for sewage and water drainage

When replenishing oil from the oil conservator or filtering oil with electricity, drain the water in the oil conservator first.

Do not enter the oil from the lower part of the power transformer to prevent moisture, air or impurities at the bottom of the oil tank from entering the power transformer body.

When the gas relay sends out a light gas action signal, the gas relay should be checked immediately, and gas samples should be taken for inspection in time to determine the gas composition.

At the same time, take an oil sample for chromatographic analysis, find out the cause and eliminate it in time.

Check whether the oil seal and oil level of the respirator are normal to ensure smooth flow. The desiccant should be kept dry and effective.

Before power transformers that have been out of service for more than 6 months are put into operation again, relevant tests shall be carried out in accordance with the requirements of the pre-test regulations.

For power transformers with excessive water content in the oil or poor body insulation performance, if they are out of service in the cold winter for a period of time, a vacuum heating oil filter must be used for hot oil circulation before being put into operation.

Strengthen the sealing monitoring of submersible pumps and oil storage tanks. If the sealing is found to be poor, it should be dealt with in time.

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About Bin Dong

Hello, I am Bin, General manager of Daelim which is a leading transformer manufacturer. As a expert, I am glad to share my experience in transformer to you. I believe our professional team can always provide you with high quality service and we are ready to provide you with one stop solution. If you have problems when you are looking for the equipment, what you need to do is tell us.