To find the mechanism of turn-insulating fault caused by switching-off shunt reactor in 35 kV system

which is of an important significance to the manufacturing process of dry-type air core reactor and improve its reliability

we researched the system overvoltage of the dry-type air-core reactor and distribution of the inter-turn electric field based on the field tests

ATP-EMTP

and finite element simulations. The space charge properties in inter-turn insulation were also measured. The analysis results indicate that the over-voltage caused by switching-off shunt reactor is 2.0 p.u. with R-C protector on the reactor’s side

but the accumulation effect of overvoltage can lead to the degradation of insulation. The distortion of electric field intensity resulting from the gap between turn-to-turn insulation is 5.5 times. In addition

the influence of thermal aging on the change of space charge characteristic and the decrease of breakdown voltage are the main factors that lead to the breakdown failure of turn-to-turn insulation of 35 kV dry-type air-core.