In this paper

the fault of 35 kV dry type air core reactor is analyzed based on the combination of insulation material

service environment and transients of operation mode. It is found that the main reason of the fault is the low thermal withstand level of insulation material and the frequent switching of capacitor bank

leading to insulation breakdown between partial turns of winding and significant increase of current. The high temperature due to high current induces inter-turn short circuit of winding at relative weak insulation place. The precautionary measures are proposed which provide assurance for safe operation of reactor.