Operating Modes of Oil-Immersed Transformers

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The operating voltage of a power transformer should generally not exceed 105% of the operating tap voltage, and must not exceed the system's maximum operating voltage. For special applications, operation at up to 110% of the rated voltage is permitted.

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The top oil temperature of an oil-immersed transformer should not exceed the specifications stipulated in the operating procedures or by the manufacturer. For transformers with forced oil circulation and water cooling, the top oil temperature should generally not frequently exceed 700℃.

Transformers with forced oil circulation cooling should be able to switch the cooler on and off according to temperature and/or load control.

Transformers in operation should have their instrument readings monitored frequently to promptly understand their operating status. If defects or abnormal phenomena are found, measures should be taken to eliminate them promptly. If the problems cannot be eliminated immediately, monitoring must be strengthened to prevent the accident from escalating, and countermeasures should be determined as soon as possible.

1. Transformer Cooling Water System Supply Method

When the transformer is under load, the cooling water is generally taken from the technical water supply pipe of the unit. When operating under no-load, the cooling water is generally taken from the power station's common water supply main pipe and pressurized by the no-load cooling water pump before being supplied to the transformer.

2. Transformer Cooling Water System Drainage Method: Under normal circumstances, the cooling water for the transformer under no-load and load conditions is discharged to the tailrace pipe of the unit via the main drain pipe of the unit's technical water supply system. Each transformer's drain pipe is equipped with a connecting valve. The connecting valve is normally closed. When it is required that the unit's tailrace pipe be emptied while the transformer is still operating under narrow load, the connecting valve between this transformer and a neighboring transformer can be opened to discharge the no-load cooling water to the tailrace pipe of other units.