When exposed to high temperature, insulating paper found in transformers breaks down and results in a reduction of the useful life of the transformer. Monitoring temperature of the insulating paper via a winding hot spot ensures the insulating paper is not exposed to high temperatures and helps minimize damage.
Conventional methods of monitoring the winding hot spot use calculations to simulate the temperature, but do not measure it. These winding temperature indicators (WTIs) infer the hot spot temperature by measuring the transformer load on a single phase and the surrounding oil temperature and then apply a model. Other issues with the WTIs include a long lag time (up to 5 hours) and actual temperature variance (up to 20 °C).