Oil filling, installation and records for transformers

Oil filling

Fill the fuel tank with qualified transformer oil. When conditions permit, vacuum oil injection can be used. Vacuum oil injection can effectively remove the gas and moisture in the transformer body and insulating oil, which is of great significance for improving the insulation level of the transformer. During vacuum oil filling, the oil conservator (oil pillow) should be isolated, that is, remove the safety airway diaphragm and temporarily seal it with an iron plate. When filling oil, the oil temperature should be higher than the body temperature to prevent the condensation of water. The vacuum oil injection time is generally not less than 6h, because the flow rate is properly controlled, the vacuum degree can be maintained at a certain value, which is conducive to the extraction of gas and water. The vacuum degree of the transformer is generally not less than 4.65×10-4Pa (equivalent to 350mmHg). The limit allowable value of vacuum pumping for different types of transformers: 35kV transformer capacity is not more than 0.051MPa when 4000~31500kVA; 110kV transformer capacity is not more than 0.051MPa when 1600okVA; 220~330kV transformer should not exceed 0.101MPa, and the elastic deformation degree of the oil tank should be monitored during vacuuming, and the maximum value should not exceed 2 times the wall thickness. The method can fix a measuring rod on the basis of the transformer, and install a stylus on the rod. Before vacuuming, the stylus is just in contact with the fuel tank. During the vacuuming process, the degree of deformation of the fuel tank can be judged by measuring the trace between the stylus and the fuel tank. The transformer should continue to maintain a vacuum for 2 hours after oil filling. When filling oil, the oil should be fed from the oil valve at the lower part of the transformer tank, so that the gas can be discharged easily. When filling the supplementary oil, it should be injected through the oil pillow to prevent the gas from being stored in a certain position of the body or in the gas relay, which may cause local insulation reduction or malfunction. The oil should be added to a point slightly higher than the specified oil level, because the filling gap of the oil should be considered, and it is necessary to observe whether the indication of the oil gauge is correct and whether it is consistent with the actual oil level.

When the oil filling is about to be completed, the air vents in the fuel tank, casing, riser, gas relay, radiator, oil purifier and safety airway should be exhausted several times until no air overflows, and the air holes should be resealed.

Electrical test

After oiling, let the transformer stand for 24 hours, and do various electrical tests after maintenance.


Return the transformer to the original installation position, and align with the positioning mark before maintenance. After the transformer is installed in place, the top cover of the transformer should have a rising slope of 1%~1.5% along the airflow direction of the gas relay, as shown in Figure 1. Its purpose is to allow the gas generated in the tank to easily flow into the gas relay.

After the transformer is in place, use the wheel stopper and screws as shown in Figure 2 to fix the transformer firmly.

Oil filling, installation and records for transformers
Figure 1 – Installation slope of the box cover and gas maintenance appliances

1-Whole iron; 2-Gas-dimensional electrical appliances; 3-Track 4-Wheels on the chassis; 5-Braking iron

Oil filling, installation and records for transformers
Figure 2 – Schematic diagram of wheel stop installation

1-wheel stopper; 2-rail

Connect the casing lead

Connect the fan motor power supply and check the steering again. Connect the gas relay and the signal thermometer power supply, and connect the ground wire.

Make assembly records

Record the installation time, sequence, test data, oil level, and insulation resistance of each component of the transformer.