Study on the DC Flashover Characteristics of Insulation Barrier-LN2-Bubbles Composite Systems With Different Voltage Rise Rates in Both Polarities

Barrier effect is an effective way to improve the insulation strength of the resistive-type superconducting fault current limiters (R-SFCL). However, thermal bubbles generated during the quenching of the R-SFCL will induce the flashover of R-SFCLs. The objective of this paper is to investigate the DC flashover characteristics of insulation barrier-LN
₂
-bubbles composite systems with different voltage rise rates in both polarities. In this paper, a needle-needle-plane electrode was used in the test to simulate the quenching state of a superconducting coil. A heater source which heat flux was 27 W/cm
²
to generate the thermal bubbles. The high voltage was applied to one needle electrode. And the DC voltage rise rate was 0.5 kV/s, 1 kV/s and 3 kV/s, respectively. The other needle electrode and the plane electrode were connected to the ground. The results showed that with the DC voltage rise rate increases, the flashover voltage of the insulation barrier-LN
₂
-bubbles composite systems also increases in both polarities. In the case of the bubbles, the flashover voltages are nearly the same in both polarities under the same voltage rise conditions. In the absence of bubbles, the flashover voltage of the positive polarity is higher than that in the negative polarity under the same voltage rise rate. The results can be applied to the high voltage level design of the R-SFCL.