Cooling Methods of Transformer | The Definitive Guide

Cooling Methods of Transformer

Hello friends, let’s see in today’s article what kind of method is used to keep the transformer cool. The cooling method in a transformer is to dissolve the heat generated in it. Various methods have been used for this.

No transformer is an ideal transformer so there will be some loss due to heat. Most of the time this heat is converted but if this heat does not melt properly then this high temperature becomes the main problem of insulation failure of the transformer.

From this, it is clear that the transformer needs a cooling system. Various factors are responsible for generating the main heat in the transformer which can lead to damage like hysteresis, eddy current, iron, and copper damage.

Suggested Read: What Is an Oil Circuit Breaker? | A Complete Guide

Transformers Can Be Divided Into 2 Main Types

#1. Dry-type Transformers.
#2. Oil-immersed Transformers.

Thus the cooling system is also different.

Dry-type transformers include 2 methods no one is Air Natural and the second is Air Blast.

Oil-immersed transformers include 4 methods

Sr.No. Cooling Methods
#1 Oil Natural Air Natural (ONAN)
#2  Oil Natural Air Forced (ONAF)
#3 Oil Forced Air Forced (OFAF)
#4 Oil Forced Water Forced (OFWF)

Method of Cooling Dry-type Transformers

#1. Air Natural

This type of method is commonly used in small transformers. In this system, the heat generated in the transformer is cooled by the circulation of natural air.

When the temperature of the transformer rises above the temperature of the air around the transformer, hot air escapes due to the natural air convection process and is replaced by cold air. This method is also known as a self-cooled method. This method is mainly used for up to 3 MVA.

#2. Air Force (AF) or Air Blast

This method is used in transformers larger than 3 MVA. Natural air is not enough for this so in this method the pressurized air is cooled in the transformer. Thus with the help of a fan and blower, the pressurized air is pushed into the core and winding of the transformer. An air filter is used to keep dust particles out of the ventilation pipe.

When the temperature of the transformer exceeds the specified temperature an alarm is activated and the fan and blower are turned on automatically. This method is suitable for transformers up to 15 MVA.

Suggested Read: What is Transformer Oil? | A Complete Guide

Cooling Methods For Transformers Immersed In Oil

#1. Oil Natural Air Natural (ONAN)

This method uses natural air. Thus the core and winding of the transformer are placed in a tank filled with oil. As the core and winding temperature rise, the oil moves to the top.

Oil Natural Air Natural

And in this empty space, the oil in the radiator takes its place. The oil in the upper part releases the heat in the atmosphere due to the cold air around here and cools itself. And stays in the radiator again. This type of cooling is used in transformers up to 30 MVA.

#2. Oil Natural Air Forced (ONAF)

In this type of method, heat loss can be prevented by applying compressed air to the heat-releasing surface. The pressure also cools the transformer faster than natural air.

Oil Natural Air Forced

In this method, the fan and blower are installed near the radiator. The fan and blower turn on automatically when the temperature of the transformer exceeds the specified temperature.

This method is commonly used for large transformers up to 60 MVA. This costs more than the other process as in other processes oil and air are handled naturally but thus fans and blowers are used as additional equipment for oil cooling.

Suggested Read: What is a Step-Down Transformer? | The Definitive Guide

#3. Oil Forced Air Forced (OFAF)

This method is known by its name. Air and oil are used for forcibly cooling the transformer. Thus a heat exchanger is fitted in which hot oil is pumped out. The air is passed through this heat exchanger by turning on the fan.

Oil Forced Air Forced

This method is very similar to Oil Natural Air Natural. The same system works when the load across the transformer is low. When the load on the transformer increases, the heat also increases. This is why it has an alarm set that automatically turns on the pump and fan as the temperature rises. This cooling system is used in substations and power stations or where higher-rating transformers are used.

#4. Oil Forced Water Forced (OFWF)

This method is exactly the same as Oil Forced Air Force. It also has a heat exchanger. The heat exchanger is used to separate heat with the help of pressurized water.

Oil Forced Water Forced

The oil level and pressure are always kept higher than the water. If there is a leakage in the system, the oil collects in the water but the water does not dissolve in the oil. This type of cooling system is commonly used in very large transformers with a 100 MVA rating. Or space where the banks of the transformer are installed. This system is usually used for transformers installed in hydropower plants.

Like this post? Could you share it with your friends?

Suggested Read –

Hey, I am Vishnu Patil and I'm an Electrical Engineer and Electrical maestro. I have more than 10 years of experience with electricals. Through ElectricalGang I want to spread my knowledge with everyone else.

Leave a Comment