Monitoring of winding temperature in power transformers — A study

The condition monitoring of power transformers is of great importance, while considering the reliability and safety issues in a power system. Thermal stress is one of the main parameter that has to be monitored. Drastic variations in the temperatures of transformer winding, oil, insulating medium etc have effects on the operating conditions, life cycle and safety of the machine. A wide literature review has been done to identify an efficient technique for the thermal stress monitoring in power transformers. A study of the selection of hotspots for temperature monitoring, types of sensors used, advanced and efficient monitoring techniques, etc have been discussed in this paper. Direct and indirect thermal stress monitoring techniques have been discussed and compared to select an appropriate technique for the implementation of a pre-fault detection system in power transformers. After the literature survey, fibre optic sensor based thermal stress monitoring techniques found to be apt for the aforementioned application.