Influence of spike defect on the impulse breakdown characteristics of SF6 gas gap in GIS

By using 1 MV Marx generator and a 220 kV GIS bus, an experiment platform has been established, and a stainless steel needle is applied to simulate spike defect, so as to study the influence of pressure, wave front time and electric field on 50 % breakdown voltage (U
₅₀
) and voltage-time (V-t) characteristics of SF
₆
gas gap with existence of a spike defect on the bus of GIS under double exponential impulse voltage. When wave front time is short, 50% breakdown voltage of the SF
₆
gap hardly changes with various pressures, and U
_50%
-P curve turns to be a hump shape when wave front time increases. However, pressure has no significant effect on V-t characteristics. The slope of V-t characteristics curve is negative when wave front time of applied voltage is short (0.08~0.9μs), and it will turn to be positive when wave front time becomes longer (several ~15μs). A new method to fit these V-t characteristics curves under impulse voltage with longer wave front times is proposed. It is found that 50 % breakdown voltage decreases almost linearly with the increase of electric field non-uniformity factors (f), and V-t characteristics cluster with valley-like profile have been drawn at different f. Dispersion of V-t characteristics cluster reduces and the flat region expands with the increase of f, and minimum value of breakdown voltage of SF
₆
gap with spike defect under impulse voltage, which is of guiding significance for engineering, can be obtained.