Purpose/Aim

Nonlinear resistive field grading material (FGM) is capable of homogenizing the partial electric field, and is widely used in cable terminals, motor end insulation and bushing. Many researches have been carried on the material modification and engineering application of FGM, but the long-term stability of FGM is rarely reported. In this paper, we aim to study the influence of thermal aging on the nonlinear conductivity and dielectric properties of FGM.

Experimental Details

The silicon carbide (SiC)/epoxy resin (EP) micro-composites are prepared with a filler loading of 30 wt%. Thermal aging experiments are carried out on the composites at 120, 150 and 180 ^oC, respectively, for 45 days. The nonlinear conductivity and dielectric properties of SiC/EP micro-composites are measured by using a three-electrode test system and a broadband dielectric spectrometer, respectively. The DC breakdown strength of the composites is also measured. The microstructure is characterized by Fourier transform infrared spectroscopy (FTIR).

Results and discussion

The experimental results show that, when the aging temperature is 180 ^oC, the current density of SiC/EP micro-composites under 5kV/mm decreases first and then increases with the increase in aging time. When the aging time reaches 30 days, the nonlinear coefficient of composites increases obviously. With the increase of aging time, the relative permittivity and loss tangent of composites increase gradually, and the DC breakdown strength decreases gradually. When the aging time is the 45^th days, the current density of composites increases gradually with the increase of aging temperature under 5kV/mm, and the nonlinear coefficient of aged composites is significantly different from the unaged ones. With the increase of aging temperature, the relative permittivity and loss tangent of composites increase gradually, and the DC breakdown strength decreases gradually. FTIR spectra show that the degradation of the aged composites is mainly caused by the fracture of ether bond and the generation of carbonyl group of epoxy matrix.