The HVOLTC1 controls the on-load tap changer, this is the only moving part connected to the transformer circuit. Therefore, the detection of on-load tap changers has attracted increasing attention. In the "Regulations for Handover and Preventive Tests of Electric Power Equipment", it is required to check the operation sequence of on-load tap changers and measure the switching time, etc. This instrument is mainly used to measure the transition waveform, transition time, dynamic resistance values at each tap