ONAF Transformers: What You Need to Know

24 April 2023

ONAF transformers are a type of transformer that utilizes a cooling technique where oil circulation is facilitated conventionally and through fans. ONAF transformers are primarily applied to power transformers.

ONAF Cooling Technique

The ONAF cooling technique relies on the circulation of oil within the transformer tank, aided by atmospheric air and fans. ONAF stands for Oil Natural Air Forced, signifying its method of utilizing conventional oil circulation with the assistance of forced air. This forced air helps in cooling the transformer.

Operating Principle of ONAF Cooling

In the ONAF transformer cooling technique, the oil inside the transformer tank undergoes a continuous circulation. The cooling of the oil is achieved through increased interaction with the atmosphere and external air currents.

To enhance the surface area for interaction, components such as corrugated walls, tube radiators, or radiators are mounted inside the transformer tank. This enlarges the surface area and, with the aid of an internal fan, accelerates the cooling rate.

In summary, ONAF transformers work on the principle of heat molecules within the oil moving upwards, displacing cold molecules, and passing through radiators or corrugated walls. The heat is then easily dissipated into the atmosphere, resulting in the cooling of the transformer.

Features of ONAF Cooling

The most notable features of the ONAF cooling system include:

• It is a long-lasting and high-quality cooling system.
• It is practical to use as it does not require a pump.
• Heat transfer can be two-stage, depending on the number of fans used or activated.
• The cooling control system is complex.
• Fan motors require periodic maintenance to prevent long-term failures or damage. Regular maintenance extends their operational lifespan.
• It is easy to install and does not occupy much space.
• The effectiveness of ONAF cooling is directly related to increasing the surface area. Therefore, maximizing the surface area inside the transformer tank is essential for efficient and rapid cooling. In this technique, fans are mounted near the radiator to ensure that the temperature remains below a certain threshold.

Technical Specifications of ONAF Transformers

ONAF transformers have an expansion tank and radiator-type structure and can have power capacities of up to 12,500 kVA. Their voltage rating can reach up to 36 kV.

Trans-El provides high-quality service with ONAF transformer shipments developed in compliance with international standards.