Cast resin distribution transformers

Cast Resin Transformers (CRT)are dry type Transformers and maintenance free .The cost of maintenance is very low compared to OFT. Insulation failure due to over heating of winding is the cause for failure of Transformer winding. To monitor rise of temperature in CRT temperature sensors are located at various points inside winding and are connected to the tripping controls of the breakers. There is possibility of failure of these sensors and electronic controls .If the failure is not timely located and rectified it can cause permanent damage to the transformer as breaker protection will become in effective. The only solution is to increase number of sensors and to place them uniformly.This will enable the protective tripping prompt and avoid transformer failures. Though Manufactures say that CRT are maintenance free it is always advisable to carry out routine cleaning of dust specially when the transformers are installed outdoor.Dust formation along with moisture causes insulation failure and flash over .If proper care is taken during manufacture ,there is no reason for failure of CRT . The quality of the transformer is most important .If air bubbles remain in the castings it will cause insulation failure.If the transformer fails once it is not repairable.

I have replaced the oil filled transformers in most of the substations but in last ten years not a single transformer has failed.