The winding is the component with the highest temperature within the transformer and it is the component which is subjected to the fastest temperature increases as the load increases. Therefore for the control of the temperature parameter within the transformer, the temperature of the winding, as well as top oil, is measured. The temperature of winding of Transformer is measured using Winding Temperature Indicator (WTI) and the temperature of Transformer Oil is measured using Oil Temperature Indicator.
The purpose of WTI is to indicate the winding temperature of HV and LV winding of the Transformer and operates the alarm, trip and cooler control contacts
As can be seen from the below figure, Black needle shows the current winding temperature while the Red needle shows the highest winding temperature reached for a particular day. This Red needle needs to be reset manually.
Also, for setting winding temperature for Alarm and Trip, two knobs are provided. The Green knob shows the setting of winding temperature for Alarm and Red knob shows the Trip temperature setting as shown in below figure.