What Is ONAF Transformer? What Are Its Features?

9 May 2023

ONAF (Oil Natural Air Forced) transformer is a cooling technique used in power transformers. In ONAF transformer systems, oil circulation is conventional, and air contact is provided through fans.

In the system, the heat produced by the transformer coil increases the temperature and kinetic energy of the oil. The heated oil molecules move upward in the tank and exchange places with the cold oil molecules present there.

Subsequently, the oil molecules pass through wave walls or radiators depending on the mechanical structure of the transformer. The airflow provided by external fans to these cooling units ensures that the oil molecules transfer their heat to the atmosphere more quickly, thus cooling the system.

Increasing the contact surface of the oil with the atmosphere and delivering airflow to the heated surfaces from the outside through fans are factors that accelerate the cooling of the oil in this system.

In ONAF transformer cooling systems, wave walls or radiators are mounted on the transformer tank, thereby increasing the surface area of the tank. Fans in this system are mounted under or beside the radiator, and the system comes into operation when the temperature exceeds a certain threshold.

Features of ONAF Transformer Cooling Systems

ONAF transformer cooling is a frequently used technique in power transformers. The system allows conventional oil circulation and uses fans for air contact.

Here are the features of ONAF cooling systems:

1. ONAF transformer cooling systems occupy a small space.
2. Regular maintenance of fan motors is required in this cooling system.
3. Only the coolers experience power loss when the fans are running in the system. Control of the coolers in the system can be complex.

Advantages of ONAF Cooling Systems

ONAF, a commonly used cooling system in power transformers that enables conventional oil circulation and uses fans for air contact, offers several advantages, including:

1. There is no need for pump usage in the system.
2. Long-lasting systems.
3. Heat transfer can be done in a dual-degree manner depending on the status of the used or closed fans.

Disadvantages of ONAF Cooling System

The disadvantages of the ONAF transformer cooling system are as follows:

1. Fans require maintenance and replacement throughout the transformer’s life.
2. Compared to ONAN applications, the noise level of the system is higher.