Flashover Characteristics along Coil Insulation under Intense Gamma-Ray Irradiation

The results of an experimental investigation of the surface flashover under an intense ⁶⁰Co γ-ray irradiation in air are reported. The AC voltage of 50 Hz was applied to model coils under an exposure rate of 1×10⁶R/h. It is found that flashover voltages (FOV) of the model coils are not affected at this exposure rate. The FOV of sphere gap and along polymeric cylindrical bar were also measured under irradiation, showing a slight decrease for the sphere gap at an exposure rate of 4×10⁵R/h.

Further, results obtained from flashover tests for DC voltage under an extremely high exposure rate of about 10¹³ R/h with pulsed X-ray beam show a significant decrease of FOV for the sphere gap and a slight decrease for the cylindrical bar. These results are closely related to whether partial discharges exist before the flashover or not.

Considerations on the effect of the intense irradiation on the flashover characteristics are presented qualitatively.