Internal Cooling System used in Transformer

Internal Cooling System used in Transformers

Transformers cooling systems differ with their type or design. Most common is natural cooling by surrounding air Small electronic transformers need no extra cooling. Few high frequency transformers may be fitted with heat sinks, or mounted on conducting surfaces.

Power transformers, particularly in power / grid systems generate considerably higher heat quantity and need cooling. This is done by different ways-

For dry type transformers -

1. Natural cooling by air , or self air cooled transformers — (AN) — This is common in small transformers even up to 3 MVA
2. Forced air cooling / Air blast cooling- Fans or blowers are used for cooling

For Oil Filled Transformers-

1. Oil natural Air Natural —( ONAN)- Oil filled transformers are cooled by surrounding air by convection. These often use radiators to facilitate cooling by convection through them. Heat is taken away by natural Air currents of surroundings. Transformers up to 30 MVA are usually cooled this way.
2. Oil Natural Air Forced (ONAF) — These transformers are provided with radiators and cooled by surrounding blast or fans to take away air from radiators, designed to expose maximum surface for cooling. Transformers up to about 60 MVA are cooled this way.
3. Oil Forced Air Forced (OFAF)— Oil is circulated in tank by oil pumps, and forced through heat exchangers. Compressed air is forced over these exchangers to cool them. Often the exchangers may be little away from tank and connected by pipes to tank. Such cooling may be apt near substations for large transformers.
4. Oil Forced Water Forced (OFWF) — This is used for very large transformers where rating may go in hundreds of MVA. Forced Water is used along with forced oil circulation, to remove large amount of heat.