Online Detection Technology Of High Voltage Cable Insulation By Double Differential CT With Compensation

With the continuous improvement of the voltage level of urban power grid,the amount of high-voltage XLPE insulated power cable keeps increasing.As the highvoltage cable line of urban power grid,its security is concerned by power companies.Therefore,it is very important to improve the management and operation maintenance of the high-voltage cable line.In addition to infrared temperature measurement technology and other on-line detection technology in the practical application of the project,there is no direct detection technology for the aging state of cable insulation.In this paper,aiming at the deficiency of the previous research,an improved scheme,double differential CT method with compensation,is proposed.The principle of double differential CT method with compensation is to add compensation winding in the head end CT and eliminate the influence of load current by physical compensation.This solves the problem that the error value caused by the mathematical difference between the head end measurement results is greater than the leakage current value of cable insulation aging in the original method.Then based on the improved scheme,the simulation model of double differential CT with compensation is built in the Simulink component of MATLAB.The simulation results show that the output value of the secondary differential has a positive correlation with the specific phase insulation aging state,that is,the deeper the aging degree is,the larger the output value is,which verifies the correctness of the proposed improvement scheme.On the basis of simulation,a physical simulation test system of double differential CT method with compensation is built.The test system includes FPGA control system,current transformer,voltage control current source,amplitude and phase modulation circuit and other modules.The feasibility of the test technology is further verified by physical simulation experiments.In practical engineering,in view of the non-zero output problem of A,B and C three-phase CT caused by the non-uniform characteristic parameters such as CT ratio difference and angle difference when the cable does not age,the solution is proposed,that is,in the simulation model,the signal compensation is carried out for the CT with inconsistent characteristic parameters at the head and the end,so as to eliminate the interference caused by this influence factor on the test technology.