Effect of Space Charge on Stationary and Transient Electric Field Distribution of HVDC Cable Joint

Abstract

The conversion of AC XLPE cable lines into direct-current (DC) operation has been proven to be an effective means to improve the transmission capacity of the system. Prefabricated joints are the weakest points of a cable line because of the complex structures, and composite interfaces contained. Therefore, it is of great theoretical and engineering significance to study the field strength distribution of XLPE AC cable prefabricated joints under DC voltage, effectively evaluate their DC tolerance characteristics, and provide a basis for the construction and transformation of XLPE cable DC distribution network system. This paper takes the silicone rubber (SIR), and ethylene-propylene-diene monomer (EPDM) prefabricated joints of 10kV XLPE cables as an example, the cable joint temperature field, and electric field coupling simulation model is established by the finite element analysis software COMSOL Multiphysics. The steady and transient electric field simulation of the joints under different DC voltages and load conditions are carried out considering the influence of space charge. The results show that with the increase of applied voltages and load level, the space charge injection increases, and the maximum steady state field strength in the joint is concentrated at the root of the stress cone, showing an increasing trend. Compared with the SIR joint, the field strength in the EPDM joint is higher. The capacitive component of the field strength in the joint is proportional to the peak value of the impulse voltage under the DC superimposed impulse voltage. In other words, the transient electric field equation meets the superposition principle applied.