Third harmonic index as a diagnostic tool of high-voltage varistors

High voltage varistors that consist of grained ZnO have to be tested before assembling. The recommended method for standard industrial testing of varistors demands application of high voltages and intensive currents that is inconvenient and needs extensive power consumption. This method requires also metallization of the ZnO structures that increases a cost of testing. Another method of varistor quality and endurance evaluation by the third harmonic index measurement at relatively low voltage range has been proposed. In this experimental study, we present results of the third harmonic index measurements in the selected varistors types. The applied measurement system and results of the THI (Third Harmonic Index) measurements for the selected high-voltage varistor types have been presented. It was proved that the proposed procedure can be applied for preliminary selection of the tested 280 V structures at their fabrication stage.