Transient Response Characteristic and Improved Degradation Assessment of ZnO Arresters Under Broadband Harmonic Excitation

Existing methods for arrester analysis mainly rely on static voltage sharing and steady-state parameters and thus cannot adequately represent transient responses under broadband excitation. To address this, a dynamic arrester model is established that considers the coupled electrical, thermal, and frequency characteristics of ZnO. Under power-frequency AC excitation containing broadband harmonics and fast-front impulses, the axial potential distribution and transient temperature rise in the varistor column are analyzed. On this basis, formulas for key degradation parameters under harmonic conditions are developed and verified by electrothermal experiments. The results indicate that under transient excitation, the peaks of potential and temperature rise tend to concentrate near the bottom of the varistor column; over a longer time scale, the peak region gradually shifts toward the middle of the column. This trend becomes more evident as frequency and wavefront steepness increase. Finally, an improved measurement parameter based on gradient potential ΔU and transient temperature rise ΔQ is proposed, providing a reference for arrester evaluation under broadband conditions.