Experimental investigation on the response characteristics of metal oxide varistors under very fast transient overvoltage

According to the wave characteristics of the very fast transient overvoltage (VFTO) obtained from the full-scale 1000 kV gas-insulated metal-enclosed switchgear (GIS) test circuit, the wave parameters of metal oxide varistors (MOV) experiment platform was determined, the very fast wave front impulse voltage test circuit with the front time of 20 ns was designed and set up, five different specifications of representative MOV were chosen as samples, and, the V-I characteristics of MOV, under the impulse voltage wave with the front time of 20 ns, as well as the current peak ranging from 0.5 kA to 2 kA, were investigated. Experimental results show that when the current peak keeps constant, the residual voltage under VFTO with a front time of 20 ns is approximately 14.7%~18.2% higher than under the standard lightning impulse voltage (LI). MOV expresses different impedance characteristics under VFTO, and MOV expresses resistive property when the applied voltage equates to the impedance converting voltage U₀. If the applied voltage is below U₀, MOV expresses capacitive property. As long as the applied voltage is above U₀, MOV expresses inductive property. Furthermore, the ratio of U₀ to DC reference voltage U_1mA has little relationship with the diameter and shape of MOV. The voltage shares the same moment of the zero point and they respond simultaneously. The MOV responds immediately under VFTO with a front time of 20 ns.