Waveform Distortions During Power Frequency Testing of Metal Oxide Varistors: Their Origin and Effect on Average Power Dissipation

While it is well known that a Metal Oxide Varistor (MOV) heavily distorts the voltage wave of a high-current lightning impulse, less has been said about waveform distortions observed during power frequency testing. This paper shows that significant distortions are likely produced by practical generators during power frequency testing of MOVs, with the effect that average power dissipation of MOVs and surge arresters is severely impacted by generator setup. Four distribution transformer configurations with different output impedances were used to apply 60 Hz voltage waves to a conducting, 5 kV-rated MOV at six peak current levels. Distortion was found to be a function of generator impedance and current magnitude. In one typical experiment, even a slight distortion (V<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">rms</sub> / (V<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">peak</sub> / <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\surd {2}$</tex-math></inline-formula>) = 1.014) led to 33% decrease in average power dissipation compared to that of a distortion-free wave of the same rms voltage. Without consideration of these effects, seemingly minor differences in procedure can cause parts to erroneously pass or fail tests prescribed in IEEE C62.11 (2020) or IEC 60099-4 ed. 3.0, leading to arresters not meeting manufacturers' 60 Hz TOV claims. A method is also outlined to correct for waveform distortion, enabling calculation of distortion-free average power dissipation.