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

ZnO varistors with various formulation, such as A-E, were fabricated according to 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 1130degreesC was consisted of ZnO grain(ZnO), spinel phase (Zn(2.)33Sb(0.67)O(4)), Bi-rich phase(Bi2O3) and intergranuler phase, wholly. Lightning impulse residual voltage of A, B, C and E's varistors suited standard characteristics, below 12 kV at current of 5 kAkA. 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 a.c. stress (115degreesC/3.213 kV/300h). Consequently, C's varistor exhibited a thermal run away. On the contrary, leakage current and watt loss of A and C's varistors which show low initial leakage current exhibited constant characteristics. After high current impulse test, A's varistor has broken the side of varistor but impulse current flowed. On the contrary, E's varistor exhibited good discharge characteristics, which the appearance of varistor was not wrong such as puncture, flashover, creaking and other significant damage. After high current impulse test and long duration current impulse withstand test, E's varistor exhibited very high characteristics which variation rate of residual voltage is 1.4% before and after test.