- Transformer Cooling System Definition: A transformer cooling system is defined as methods used to dissipate heat generated in transformers to prevent damage and ensure efficiency.
- ONAN Cooling: ONAN cooling uses natural oil and air circulation to cool the transformer, relying on convection for heat dissipation.
- ONAF Cooling: ONAF cooling employs fans to blow air over the transformer, enhancing heat dissipation by forced air circulation.
- ODAF Transformer: The ODAF (Oil Directed Air Forced) transformer uses directed oil flow and forced air to cool high-rating transformers efficiently.
- OFAF Cooling: OFAF cooling combines oil pumps and air fans to circulate oil and cool the transformer quickly and efficiently.
The main source of heat generation in transformer is its copper loss or I2R loss. Although there are other factors contribute heat in transformer such as hysteresis and eddy current losses but contribution of I2R loss dominate them. If this heat is not dissipated properly, the temperature of the transformer will rise continually which may cause damages in paper insulation and liquid insulation medium of transformer. So it is essential to control the temperature with in permissible limit to ensure the long life of transformer by reducing thermal degradation of its insulation system. In electrical power transformer we use external transformer cooling system to accelerate the dissipation rate of heat of transformer. There are different transformer cooling methods available for trans former, we will now explain one by one.
Different Transformer Cooling Methods
For accelerating cooling different transformer cooling methods are used depending upon their size and ratings. We will discuss these one by one below,
ONAN Cooling of Transformer
This is the simplest transformer cooling system. The full form of ONAN is “Oil Natural Air Natural”. Here natural convectional flow of hot oil is utilized for cooling. In convectional circulation of oil, the hot oil flows to the upper portion of the transformer tank and the vacant place is occupied by cold oil. This hot oil which comes to upper side, will dissipate heat in the atmosphere by natural conduction, convection and radiation in air and will become cold. In this way the oil in the transformer tank continually circulate when the transformer put into load.
As the rate of dissipation of heat in air depends upon dissipating surface of the oil tank, it is essential to increase the effective surface area of the tank. So additional dissipating surface in the form of tubes or radiators connected to the transformer tank. This is known as radiator of transformer or radiator bank of transformer. We have shown below a simplest form on natural cooling or ONAN cooling arrangement of an earthing transformer below.
ONAF Cooling of Transformer
Heat dissipation can be improved by increasing the dissipating surface, but it becomes even faster with forced air flow. Fans blow air onto the cooling surface, removing heat more effectively than natural air. This method is called ONAF, which stands for “Oil Natural Air Forced”. Because ONAF cools faster than ONAN, electrical power transformercan handle more load without exceeding temperature limits.
OFAF Cooling of Transformer
In oil forced air natural cooling system of transformer, the heat dissipation is accelerated by using forced air on the dissipating surface but circulation of the hot oil in transformer tank is natural convectional flow.
The heat dissipation rate can be increased further by forcing the oil to circulate. In the OFAF cooling system, oil pumps circulate the oil within the transformer tank. OFAF stands for “Oil Forced Air Forced” cooling. This system is compact and provides the same cooling capacity as the previous methods but takes up less space. In natural oil cooling, heat moves away slowly due to convection. In forced oil cooling, heat is quickly moved away as soon as it enters the oil, making the cooling process faster.
OFWF Cooling of Transformer
Water has a lower ambient temperature than air, making it a better heat exchanger. In the OFWF cooling system, hot oil is pumped to an oil-to-water heat exchanger. Here, cold water showers cool the oil. OFWF stands for “Oil Forced Water Forced” cooling.
ODAF Cooling of Transformer
ODAF or oil directed air forced cooling of transformer can be considered as the improved version of OFAF. Here forced circulation of oil directed to flow through predetermined paths in transformer winding. The cool oil entering the transformer tank from cooler or radiator is passed through the winding where gaps for oil flow or pre-decided oil flowing paths between insulated conductor are provided for ensuring faster rate of heat transfer. ODAF or oil directed air forced cooling of transformer is generally used in very high rating transformer.
ODWF Cooling of Transformer
ODAF or oil directed water forced cooling of transformer is just like ODAF only difference is that here the hot oil is cooled in cooler by means of forced water instead of air. Both of these transformer cooling methods are called forced directed oil cooling of transformer.
Very interesting, thanks a lot.
I would be very grateful to get a detailed drawing of an ODAF cooling of transformer.
Regards