Function of Radiator
When a transformer is loaded, the current starts flowing through it’s windings. Due to this flowing of electric current, heat is produced in the windings, this heat ultimately rises the temperature of transformer oil. We know that the rating of any electrical equipment depends upon its allowable temperature rise limit. Hence, if the temperature rise of the transformer insulating oil is controlled, the capacity or rating of transformer can be extended up to significant range. The radiator of transformer accelerates the cooling rate of transformer. Thus, it plays a vital role in increasing loading capacity of an electrical transformer. This is basic function of radiator of a power transformer.
Oil immersed power transformer is generally provided with detachable pressed sheet radiator with isolating valves. But in case of small size distributing transformer, the radiators are generally integrated parts of transformer body and projected from the main tank. The working principle of radiator is very simple. It just increases the surface area for dissipating heat of the oil. In case of electrical power transformer, due to the transport limitation, this units are sent separately and assembled at site with transformer main body. At the time of dispatching, the flings of radiator are blanketed by gasket and blanketing plates. The radiator valves on the main tank are also blanketed by gasket and blanketing plates.
Assembling and Mounting of Transformer Radiator
Special care should be taken while removing radiators from crates and the same care should also be taken during handling and mounting the radiator bank. This is because any minor damage can initiate oil leakage from the bank as radiator units are made from very thin steel sheets of metal for good conduction of heat from oil to air. After removing from crates, these radiators must be cleaned externally. These are also required to be clean from inside by flashing with transformer insulating oil.
The radiator units must be assembled one by one that means, fitting and fixing of one unit must be completed in all respect before assembling the next unit. The assembling should be started from one side and finished at other side. Before assembling the unit, remove blanketing plates from the top and bottom radiator valves. During the removing of blanketing plates; if gasket surface is damaged, it should be replaced by new gasket. Then the radiator unit would be lifted vertically and brought nearer to the respective main tank valves. Now remove the blanketing plates of the main tank valves. Fit the radiator flange on respective valve of main tank by nuts, bolts, plain and spring washers. Assemble all the other radiator units in same manner.
After assembling all the units, this is the time for filling insulating oil. This should also be done one unit by one unit. For that, first the bottom valve is opened and air release plug on the top of the radiator is also gets slowly unscrewed. The oil from main tank will enter into the transformer radiator unit. Air starts escaping from air release plug till the unit is totally filled with transformer insulating oil. The oil filling in the unit is completed when oil comes out from unscrewed air release plug. After that, the air release plug is tightened and top radiator valve is open.
Operation of Transformer Radiator
Under loaded condition, warm oil increases in volume and comes to the upper portion of the main tank. Then this oil enters in the radiator through top valve and cools down by dissipating heat through the thin radiator wall. This cold oil comes back to the main tank through the bottom radiator valve. This cycle is repeated continuously till the load is connected to the transformer. Dissipation of heat in the transformer radiator; can be accelerated further by force air provided by means of fans. These fans are fitted either on the radiator bank itself or fitted nearby the bank but all the fans must be faced towards the radiator. Sometime, the cooling rate of convectional circulation of oil is not sufficient. That time an oil pump may be used for speeding up oil circulation.