Statistical Analysis of Low-Voltage Varistor Clamping Voltage Variability under Switching Surges

This study investigates the relationship between the number of applied switching surges and the clamping voltage response of Metal Oxide Varistors (MOVs) through bivariate statistical analysis. The clamping voltage, which marks the threshold at which an MOV becomes conductive, plays a critical role in diverting excess surge energy to the ground and limiting voltage across protected equipment. A stable and predictable clamping voltage is vital for effective surge protection. MOV samples were subjected to various surge event frequencies, with reference voltage measurements recorded before and after testing. Clamping voltage values were also measured at the beginning and end of the testing period. Scatter plot analysis revealed a slight upward trend in the clamping voltage ratio as the number of surges increased, with data narrowly clustering between 1.1 and 1.5 p.u., indicating a weak correlation. A Pearson correlation coefficient of 0.22 further supported this observation. Linear regression analysis demonstrated a negligible positive slope of 0.0008 and a low R-squared value of 0.049, suggesting that the number of surges contributes minimally to the variance in clamping voltage. These findings indicate that while repeated surge exposure may result in a slight increase in clamping voltage, it is not a reliable metric for assessing degradation levels compared to reference voltage changes. The impact of surge events on clamping voltage response remains statistically insignificant.