Transition of the Long-Term Stability of Stable ZnO Varistors Due to the Elevated Aging Temperature

ZnO varistor ceramics are important for overvoltage protections in power system owing to their outstanding nonlinear current density–electric field characteristics. Stable ZnO varistor ceramics with steadily decreasing power loss are gradually applied despite common understandings about their aging behaviors. In this study, they are employed for accelerated dc aging at an elevated aging temperature. They are found to exhibit a power loss transition during the aging. The typical “crossover” in J–E curves disappears after the transition. They continuously move to high-current regions afterwards. The further recovery experiments suggest that irreversible electrical degradation has been caused by the elevated temperature. The frequency-domain spectroscopy results show that the real part of the dielectric constant also cannot be recovered. The above results suggest the interface states of stable samples can only remain stable at a certain range of temperature. Otherwise, they would combine with mobile ions in depletion layers, causing the ZnO varistor ceramics to lose their long-term stability. The findings of the study provide a reference for establishing the condition assessment method for stable ZnO varistor ceramics.