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Transformer Cooling Methods

Table of contents

What are the types of Transformer Cooling method and their differences?

Transformer always have losses thus, generates heat. It should be rectified with proper cooling system to avoid failure. Transformer can be classified in to two types which are Dry-type and Oil-immersed Type.

  • For dry-type transformers
    1. Air Natural (AN)
    2. Air Blast
  • For oil-immersed tranformers
    1. Oil Natural Air Natural (ONAN)
    2. Oil Natural Air Forced (ONAF)
    3. Oil Forced Air Forced (OFAF)
    4. Oil Forced Water Forced  (OFWF)

Cooling methods for Dry type Transformers

Air Natural or Self air cooled transformer

This cooling system is generally used in small type transformers upto 3MVA. It is when Transformer is being cooled by air. Example is when a control transformer is inside a control panel or installed in a control room with just a housing.

Air Blast

For transformers rated more than 3 MVA. In this method, air is forced on the core and windings with the help of fans or blowers mounted in Transformer Housing. The fan ot blower must be filtered to prevent the accumulation of dust particles in vents. This cooling method can be used for transformers upto 15MVA.

Cooling methods for Oil Immersed Transformers

Oil Natural Air Natural (ONAN)

This method is used for oil-mmersed transformers. In this method, the heat generated in the core and winding is transferred to the oil inside the main tank. According to the principle of convection, the heated oil flows in the upward direction and then in the radiator. The heat from the oil will dissipate in the atmosphere by natural air flow around the transformer. In this way, the oil in transformer keeps circulating due to natural convection and dissipating heat in atmosphere due to natural conduction. This cooling method can be used for transformers upto about 30 MVA.

Oil Natural Air Forced (ONAF)

The heat reduction can be improved further by applying forced air on the dissipating surface with the use of fan and blowers. Forced air provides faster heat dissipation than natural air flow. In this method, fans are mounted near the radiator and may be provided with an automatic starting arrangement, which turns on when temperature increases beyond certain value. This transformer cooling method is generally used for large transformers upto about 60 MVA.

Oil Forced Air Forced (OFAF)

In this method, oil is circulated with the help of a pump. The oil circulation is forced through the heat exchangers. Then compressed air is forced to flow on the heat exchanger with the help of fans. The heat exchangers may be mounted separately from the transformer tank and connected through pipes at top and bottom as shown in the figure. This type of cooling is provided for higher rating transformers at substations or power stations.

Oil Forced Water Forced (OFWF)

This method is similar to OFAF method, but here forced water flow is used to dissipate hear from the heat exchangers. The oil is forced to flow through the heat exchanger with the help of a pump, where the heat is dissipated in the water which is also forced to flow. The heated water is taken away to cool in separate coolers. This type of cooling is used in very large transformers having rating of several hundreds MVA.

Credits to: Electrical4u

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