| The intricate installation environment and the different technical level of workers lead to the possibility of some defects in the installed cable joint,which is very likely to cause faults,making the joint a weak part in the cable line.Accurate analysis of the electric field intensity distortion caused by defects has great significance for further understanding of the failure mechanism of cable joints and engineering installation.In this paper,a simulation geometric model of a 10 kV cable joint of a certain manufacturer is established according to a 1:1.From the perspective of the normalized Maxwell equations,it is pointed out that the electric field distribution inside the joint is a quasi-static electric field problem.Three simulation control equations and boundary conditions based on the finite element method are discussed,and the simulation method 1 which can best characterize the quasi-static electric field is determined through simulation comparison research as the method to calculate the electric field distribution inside the cable joint.Based on the Helmholtz uniqueness theorem,a precision model which suitable for calculating the electric field distribution in the case of small-size defects inside the cable joint is proposed,and the accuracy and effectiveness of the model are verified.Through the analysis of examples,the precision model can better describe the electric field distribution near the particles,and can be widely used in the analysis of electric field distribution in accessories such as cable joint and terminals.The electric field distribution with two types of defects which are impurity particles and scratches on the surface of the cable insulation were simulated and studied by using the precision model.According to controlled variable method,the influence mechanism of the defect type,size and location on the electric field distribution is studied.The statistical analysis of these results from multiple dimensions shows that the presence of small bubbles at the interface between the cable insulation and the joint insulation does not affect the electric field distribution.When the radius of the conductive particle remained,the closer the particle is to the high-voltage shield,the greater the electric field intensity;compared to the particle position change,the electric field intensity is more sensitive to the particle size;when there are scratches on the cable insulation surface,the interface with the joint insulation is more likely to accumulate free charge and cause greater distortion of the local electric field;if insulating grease is not applied to the scratches,the electric field will increase by more than 1.5 times.After applying insulating grease,the electric field distribution can be improved to a certain extent,especially when the relative permittivity of the grease is close to that of the cable insulation,the electric field distortion is the smallest.Therefore,during the installation of the cable joint,special attention should be paid to removing the small particles on the cable insulation surface near the end of the high-voltage shield,scratches on the cable insulation surface should be avoided,and a suitable insulating grease should be selected and applied evenly on the cable insulation surface to reduce electric field distortion caused by scratches. |
