In the operation process of dry-type air-core reactors

moisture may invade the package

cause serious demp heat aging of the insulation inside the package

and eventually result in reactor accidents. However

at present the detailed process and mechanism of the demp heat aging and the fire failure of reactor have not been studied in depth. Due to the deterioration of the breakdown performance of the demp heat aging materials

the inter-turn insulation may be broken down under the action of overvoltage to form a permanent inter-turn short-circuit path and malfunction. In this paper

the possibility of such short-circuit failures is discussed and the influence of the inter-turn overvoltage on the inter-turn insulation is studied. First

the maximum overvoltage that may appear at the reactor port is analyzed. Then

the chain loop is used to calculate the maximum inter-turn overvoltage that the reactor may suffer during operation. Finally

a special reactor model containing only two turns is used to study the risk of inter-turn insulation fault by the inter-turn overvoltage. The results show that although the inter-turn insulation of the reactor

in case of suffering the overvoltage shock

is likely to withstand a large overvoltage

yet the overvoltage is not easy to damage the inter-turn insulation and lead to short circuit failure even if the inter-turn insulation is seriously aged.