Oil temperature indicator :

 Oil temperature indicator : 

OTI is the oil temperature indicator of an oil-filled transformer. Since the transformer oil is also used for cooling purposes, the temperature of the oil gives out the internal thermal condition of the transformer.

WTI is the winding temperature indicator of the power transformer. The windings of the transformer are the heat source and its temperature is always higher than the oil. The winding temperature cannot be measured directly and so it is measured via the oil temperature and a current proportional heating element.

The temperature indicators are therefore essential to know about the internal condition of the transformer. It may also be noted that with the help of this indicator, both alarm and trip signals are generated when the temperature crosses the normal working limits.