Ageing Characteristics of Silicone Rubber Insulation in Cable Joints with Different Service Years

The cable joints are important part of the power lines. But in actual operation, the long-term combined action of electricity, heat and force will lead to the gradual fracture of the molecular chains which of the silicone rubber insulation in cable joints, it will affect the electrical characteristics of the material and degrade the insulation performance. Therefore, it is of great significance to study the aging characteristics of silicone rubber insulation in cable joints during different service stages and grasp their operating conditions to improve the operation and maintenance. In this paper, the tests of conductivity-temperature characteristics, breakdown strength and dielectric spectra of the insulation layers of 10 kV prefabricated silicone rubber cable joints were conducted. The results show that the volume resistivity and the activation energy of conduction decreasing by the effect of long-term electro-thermal aging. With the increasing of operation time, the breakdown strength decreases gradually and the data dispersion increases. The relative dielectric constant and the dielectric loss of the samples increase with the operation time. In the range of measured frequency, the relative dielectric constant is practically unchanged during the same operation period. However, the free radicals and small molecules which formed by the breaking of molecular chains, lead to the increase of dielectric loss at low frequency. As the temperature rising, all samples show the relative dielectric constant decreases and the dielectric loss increases at low frequency.