Interfacial space charge between ZnO varistor ceramics and coating materials

The interfacial space charge distribution between ZnO varistor ceramics and different collar coating materials was investigated using the Pulsed Electroacoustic Method (PEA) and Thermal Stimulated Current (TSC) methods. The experimental results show that a large amount of space charge accumulates at the interface between ZnO varistor ceramics and polyester polyurethane, while there is less space charge presents at the interface between ZnO varistor ceramics and polyester modified silicone. The PEA results show that the introduction of inorganic glass between ZnO varistor ceramics and organic coating materials can greatly reduce the amount of space charge. The results from the surface flashover measurement, which was based on 4/10 /spl mu/s steep impulse current, indicated that more space charge present at the interface between ZnO varistor ceramics and coating materials will lead to lower withstanding flashover capability of ZnO blocks since the electric field can be deviated due to the existence of interfacial space charge.