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ABSTRACT: This paper determines the waveform parameters of metal oxide varistor (MOV) test platform according to the IEC standards and the waveform characteristics of very fast transient overvoltage (VFTO) measured in gas-insulated metal-enclosed switchgear (GIS). The standard lightning impulse test circuit with 8 us wave-head time, the steep wave impulse test circuit with 100ns wave-head time and the very fast transient overvoltage impulse test circuit with 20ns wave-head time are designed and constructed respectively. Several typical MOVs used in 10kV and ultra-high voltage arresters are selected as samples. The volt-ampere characteristics of MOVs under the above three different wave-head time impulses are studied experimentally. The experimental results show that the residual voltage of MOV increases by 14.7% to 18.2% under the action of 20ns very fast transient overvoltage impulse compared with the standard lightning wave and the steep wave with the same amplitude. Under the action of standard lightning impulse with 8us wave-head time and the steep wave impulse with 100ns wave-head time of different amplitude, the voltage of MOV reaches its peak value earlier than current, showing the characteristics of inductance. Under the action of 20ns very fast transient overvoltage impulse, MOV has an obvious impedance transition voltage U0. Under U0 voltage, MOV shows resistance characteristics. When the peak voltage is less than U0, MOV shows capacitive impedance characteristics. When the peak voltage is greater than U0, MOV shows inductive impedance characteristics. U0/U1mA has little relationship with the shape and size of MOV.
