Stability of Self-Adaptive Dielectrics Under Various Electrical-Thermal Stress

Nonlinear dielectrics with self-adaptive electrical parameters (SADs) are promising for field grading and stress control in key parts of high-voltage apparatus. However, the performance of SADs can be considerably affected by various electrical-thermal excitations and their reliability in these complicated working conditions should be further validated. This article has prepared SADs that consists of ethylene-propylene-diene monomer (EPDM) and silicone rubber (SR) composites with different ZnO microvaristor filler concentrations. Nonlinear V-I characteristics of the composites are measured under different thermal excitations, including wide temperature range, heat cycles, as well as local hot spots caused by transient overvoltage. The article has summarized the effect of the electrical-thermal excitations on the nonlinear conducting behavior of the composites and analyzed its mechanism, through which the reliability of SADs under these working conditions is evaluated and the influences of filler and polymer matrix property on the thermal stability of the composites are discussed. Finally, suggestions for field grading as well as material design are proposed.