Enhancement of Electro-Thermal Characteristics of Micro/Nano ZnO Based Surge Arrester

Semiconductor ceramics based metal oxide varistors (MOVs) are currently used to protect electrical equipment against internal and external overvoltages without interrupting power supply. The improved protective characteristics of surge arresters helps to reduce the cost with an excellent insulation design for electrical systems. The proper exploration of material with better non-linearity, higher breakdown voltage and lower leakage current is considered as essential parameters for proper design of modern high power, high voltage and gas-insulated substation (GIS). In this paper, varistor samples of Sample 1 (95% Micro ZnO + 2% of Micro Bi2O3 + 2% of Micro Y2O3 + 1% of Micro Sb2O3), Sample 2 (95% Nano ZnO + 2% of Micro Bi2O3 + 2% of Micro Y2O3 + 1% of Micro Sb2O3), Sample 3 (95% Micro ZnO + 2% of Micro SrO + 2% of Micro Y2O3 + 1% of Micro Sb2O3) and Sample 4 (95% Nano ZnO + 2% of Micro SrO + 2% of Micro Y2O3 + 1% of Micro Sb2O3) are prepared through sequential process, which includes ball milling, calcination (700 °C), compression (340 kg/cm2), molding and sintering (1150 °C). The prepared samples are then characterized using SEM, and experimentation is carried out to analyze the various parameters such as non-linearity, permittivity, dielectric loss and thermal conductivity. The SrO included as a principal additive component instead of Bismuth oxide in Sample 3 and 4 makes it with improved surge arrester characteristics. The results revealed that the Sample 4 attained enhancement of 40% in the non-linear characteristics is due to the increase in the active area of grain boundaries in comparison with Sample 1. In addition, the impedance spectroscopy results emphasize that the value of permittivity, resistivity and dissipation factor is better for Sample 4. Thermal analysis concluded that the thermal conductivity enhanced to 0.67 (W/cm K) for Sample 4 by exclusive formation of ZnSrO2 phase.