Transformer Cooling Method

The cooling of the transformer is the process of dissipating or treating the heat generated in the transformer to a safe value. This is achieved through various available transformer cooling methods.

The cooling method is as follows.

Dry-type transformers use the following two cooling methods:

Air Nature (AN)

Using the natural air method, the heat generated in the transformer is cooled by natural air circulation. When the temperature of the transformer is higher than that of the surrounding air, the hot air is replaced by cold air through the natural convection process. This method is also called the self-cooling method. This method is used to cool smaller output transformer ratings (up to 1.5 MVA).

Air Forced (AF) or air blast

In this method, the generated heat is cooled by forced air circulation. With the help of fans and blowers, high-speed air is pressed against the core and windings of the transformer. When the internal temperature of the transformer exceeds the standard safety level, the alarm is activated and the fan and blower are automatically turned on. This method is suitable for transformers with rated power up to 15MVA.

Oil-immersed transformer cooling methods include oil-air cooling and oil-water cooling.

Oil Natural Air Natural (ONAN)

This cooling method uses a natural convection process. The assembly of iron core and winding is placed in an oil immersion tank. As the core and windings heat up, the oil temperature in the transformer rises. Therefore, the oil moves upward and flows out from the upper part of the transformer tank. This kind of hot oil dissipates heat in the air through natural convection and conduction processes. The oil is cooled by natural air circulation and passed through the radiator for the transformer again. This type of cooling is used for transformers rated up to 30 MVA.

Oil Natural Air Forced (ONAF)

The ONAF method is used to cool transformers rated up to 60 MVA. As mentioned above, in the ONAN method, heat dissipation is carried out by the convection process of natural circulation cooling of air, but in this type, forced air is used to cool the transformer.

If the heat dissipation of the transformer will eventually increase, the heat dissipation of the transformer will also increase. With the installation of fans and blowers, high-speed air is forcibly applied to radiators and cooling towers, which will help cool the oil faster and more efficiently.

Since fans and fans are added to the method as additional cooling equipment, the cost is higher compared to another process in which oil and air circulate naturally.

Oil Forced Air Forced (OFAF)

As the name implies, both oil and air cool the transformer in a forced manner. A heat exchanger is installed and hot oil is circulated through the heat exchanger with the help of a pump. With the help of a high-speed fan, the air is forced through the heat exchanger.

This method is similar to ONAN because when there is a low load on the transformer, cooling is done by a simple ONAN method. However, once the load increases, the heat generated will also increase, so the sensor will issue an alarm indicating that the heat loss has exceeded the safe value, so the fan and pump will automatically turn on. Therefore, the OFAF method is used for cooling.

Oil Natural Water Forced (ONWF)

In the oil-natural water forced cooling method, the transformer core and winding are immersed in the oil tank. A radiator is installed outside the water tank. When the temperature rises and the oil heats up and moves upward, the heat is dissipated through natural convection. The oil passes through the radiator, but the water is pumped and cools the oil through the heat exchanger.

Oil Forced Water Forced (OFWF)

A heat exchanger is installed, and with the help of the pump, both oil and water pass through the heat exchanger. The oil level and pressure are always maintained above the water level and pressure, so that if any leakage occurs in the system, the oil will mix with the water, but the water will not mix with the oil.

This method is suitable for large-capacity transformers with a rating of several hundred MVA or transformers with installed transformer banks. This cooling method is mainly used for transformers installed in hydropower stations.

The above information is provided by oil-filled transformer factory.