The commonly used cooling methods for transformers are as follows:
1. Oil-immersed natural cooling (ONAN);
2. Oil-immersed air cooling (ONAF);
3. Forced oil circulation air cooling (OFAF);
4. Forced oil circulating water cooling (OFWF);
5. Forced guided oil circulation air cooling (ODAF);
6. Forced pilot oil circulation water cooling (ODWF).
According to the requirements of the transformer selection guide, the recommended cooling method is as follows:
1. Oil-immersed natural cooling
31500kVA and below, 35kV and below products;
50000kVA and below, 110kV products.
2. Oil-immersed air cooling
12500kVA～63000kVA, 35kV～110kV products;
Below 75000kVA, 110kV products;
40000kVA and below, 220kV products.
3. Forced oil circulation and air cooling
50000～90000kVA, 220kV products.
4. Forced oil circulation and water cooling
Generally, the step-up transformers of 220kV and above, 60MVA and above are used in hydroelectric power plants.
5. Forced pilot oil circulation air cooling or water cooling (ODAF or ODWF)
75000kVA and above, 110kV products;
120000kVA and above, 220kV products;
330kV and 500kV products.
When the strong oil-air cooling method is selected, the transformer cannot run for a long time when the oil pump and fan lose the power supply. It cannot run for a long time even with no load. Therefore, two independent power supplies should be selected for use by the cooler.
When the strong oil-water cooling method is selected, when the oil pump cooling water loses power, it cannot run. The power supply should choose two independent power supplies.
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