Common faults of oil-immersed transformers in operation include windings, bushings, tap changers, iron cores, fuel tanks, and other accessories. details as follows:

1. Winding failure

There are mainly inter-turn short-circuit, winding grounding, inter-phase short-circuit, disconnection and open welding of joints.

2. Casing failure

The fouling of the transformer bushing will cause pollution flashover in heavy fog or light rain, which will cause single-phase grounding or short-circuit between phases on the high-voltage side of the transformer.

3. Serious leakage

The oil leakage of the transformer is serious or the oil level can not be seen by the oil level gauge. At this time, the transformer should be stopped immediately to repair the leakage and refuel. The cause of the oil leakage of the transformer is weld cracking or sealing. Parts fail, the fuel tank is severely corroded and damaged by shock and external force during operation.

4. Tap changer failure

Common faults include poor contact or inaccurate position of the tap changer, melting and burns on the surface of the contact, and the discharge of the interphase contacts or the discharge of each tap.

5. Faults caused by overvoltage

When the transformer in operation of the oil-immersed transformer is struck by lightning, due to the high potential of the lightning, it will cause the external overvoltage of the transformer. When certain parameters of the power system change, due to the electromagnetic oscillation, the internal voltage of the transformer will be caused. Voltage, the transformer damage caused by these two types of overvoltage is mostly the winding main insulation breakdown, causing the transformer to malfunction.

6. The failure of the iron core

Most of the failures of the iron core are caused by the insulation damage of the through screw of the iron core column or the clamping screw of the iron core.

7. Oil leakage

The oil level of the transformer oil is too low, so that the bushing leads and the tap switch are exposed to the air, and the insulation level will be greatly reduced, so it is easy to cause breakdown and discharge.

Oil-immersed transformers should pay special attention to preventive measures for their failures to ensure normal use at ordinary times.