HOW CONDUCTANCE CHARACTERISTICS OF NONLINEAR MATERIALS INFLUENCES THE PERFORMANCE OF FIELD GRADING IN NEEDLE PLATE MODEL

The local intensified electric field, caused by structural design or charge accumulation, is the main cause of insulation problems in electrical equipment. With the field-dependent conductivity, nonlinear material is promising to be applied to electric field grade and charge suppress, which is an effective answer to the local overstress. The σ(E) relation widely used in nonlinear materials contains two variable constants, σ₀ and A, which are related to the initial conductivity and nonlinear coefficient respectively. To understand how conductivity characteristics of nonlinear material influence the effect of field grading, this paper establishes a needle plate simulation model. The nonlinear material was coated on the needle electrode to uniform the extreme electric field at the tip. The results show that the excessive initial conductivity will cause a local high electric field at the interface of air and nonlinear materials, while low initial conductivity affects the limitation of the electric field at the needle tip. The nonlinear coefficient determines the equivalent electrode size generated by the local high conductivity area of nonlinear materials. The higher the nonlinear coefficient, the greater the equivalent electrode formed, and the lower the electric field at the tip obtained.