A study on the microstructure and surge characteristics of ZnO varistor for distribution arrester

ZnO varistors with various formulations, such as A∼E, were fabricated according to the ceramic fabrication method. The microstructure, electrical properties and surge characteristics of ZnO varistors were investigated according to various formulations. In the microstructure, A-E´s ceramics sintered at 1130°C consisted of ZnO grain (ZnO), spinel phase (Zn_2.33Sb_0.67O₄), Bi-rich phase (Bi₂O₃) and intergranular phase, wholly. The lightning impulse residual voltage of A, B, C and E´s varistors suited standard characteristics, below 12 kV at current of 5 kA. On the contrary, D´s varistor exhibited high residual voltage as high reference voltage. In the accelerated aging test, leakage current and watt loss of B, C and D´s varistors increases abruptly with stress time under the first AC stress (115 °C/3.213 kV/300 h). Consequently, C´s varistor exhibited thermal runaway. On the contrary, the leakage current and watt loss of A and C´s varistors, which show low initial leakage current, exhibited constant characteristics. After high current impulse tests, A´s varistor had broken the side of varistor but impulse current flowed. On the contrary, E´s varistor exhibited good discharge characteristics, which the appearance of varistor did not show puncture, flashover, creaking and other significant damage. After high current impulse tests and long duration current impulse withstand tests, E´s varistor exhibited very high characteristics where variation rate of residual voltage was 1.4% before and after the tests.