Impedance Characteristics of Metal Oxide Varistor under Different Pulses

In this paper, the metal oxide is determined according to the characteristics of the very fast transient overvoltage (VFTO) waveform measured in the gas-insulated metal-enclosed switchgear (GIS) according to the standard regulations. The waveform parameters of the metal oxide varistor (MOV) test platform were designed to build pulse generators with 8µs, 100ns and 20ns wave-heads. Several typical MOVs for 110kV and 220kV system arresters were selected as samples. The impedance characteristics and response characteristics of MOV under the pulse of the above three different wave-head times are studied. The experimental results show that under the pulse of 8µs and 100ns with different amplitudes, the MOV voltage reaches the peak value and shows the inductance characteristics. The MOV under 20ns pulse shows different impedance characteristics. There is an impedance characteristic transition voltage U0, and at U0 voltage, the MOV shows resistivity. When the voltage peak on the MOV is less than U0, the current reaches the peak before the voltage, and the MOV mainly shows the capacitance characteristic. When the voltage peak on the MOV is greater than U0, the voltage reaches the peak before the current, and the MOV mainly shows the inductance characteristic. Under 8µs pulse, the time when the voltage and current on the MOV reach the peak value differ by 2.4µs; Under 100ns pulse, the time when the voltage and current on the MOV reach the peak value differ by 1µs; Under 20ns pulse, the time when the voltage and current on the MOV reach the peak value differ by less than 11ns. The shorter the wave-head time of the pulse, the smaller the difference between the time of the voltage and current peak value.