Operation of Oil-Immersed Transformers

The operating voltage of a power transformer should generally not exceed 105% of the operating tap voltage and must not exceed the maximum system operating voltage. Under special circumstances, operation at up to 110% of the rated voltage is permitted.
The top oil temperature of an oil-immersed transformer should not exceed the operating regulations or manufacturer's specifications. For transformers with forced oil circulation and water cooling, the top oil temperature should generally not regularly exceed 700℃.
Transformers with forced oil circulation cooling should be able to control the switching of the cooler according to temperature and/or load.
Operating transformers should regularly monitor instrumentation to maintain abreast of their operating conditions. If defects or abnormalities are detected, measures should be taken to promptly correct them. If these cannot be corrected immediately, increased monitoring is necessary to prevent further incidents.
1. Transformer Cooling Water System Supply Method
When the transformer is operating under load, cooling water is generally drawn from the technical water supply pipe of the unit. When operating at no-load, cooling water is generally drawn from the power station's common water main and pressurized by a no-load cooling water pump to supply the transformer.
2. Transformer Cooling Water System Drainage Method: Under normal circumstances, cooling water from the transformer, both when no-load and loaded, is discharged through the unit's technical water supply system drain main to the unit's tailwater pipe. A connecting valve is installed between each transformer's drain pipe. This connecting valve is normally closed. However, if the unit's tailwater pipe needs to be drained while the transformer is still operating at low load, the connecting valve between the transformer and the adjacent transformer can be opened to drain the no-load cooling water to the tailwater pipes of other units.