High-voltage Cable Insulation On-line Monitoring Technology Based On Double Differential CT Method

The development of power cables in the direction of higher voltage levels and larger capacity,which leads higher requirements on the online monitoring of high voltage power cable insulation.The traditional cable insulation on-line monitoring methods mostly obtain the electrical signal with contact-type method,so it cannot be applied to the high-voltage level;Or because the acquired electrical signal itself is easily disturbed,the measurement accuracy cannot meet the requirements.Referring to the previous cable insulation online monitoring technology,an online monitoring technology for high voltage cable insulation was proposed based on the principle of double differential CT.In this paper,the principle of double-differential CT method is described.The feasibility of double-differential CT method to monitor the insulation aging condition of high voltage cable is analyzed theoretically and the implementation scheme is given.The electrical parameters of high voltage cable are also calculated.In consideration of the three-phase cable sheathing of the metal interconnection,high-voltage cable insulation on-line monitoring simulation model was built with MATLAB software.The effects of different power frequency,end load and cable length on the method were simulated and analyzed.It was found that these factors did not affect the monitoring results.The final simulation results were consistent with the theoretical analysis and verified the feasibility of the method.Based on the theoretical analysis and simulation results,the test platform needed for the test system was built,and the operating environment of the analog high-voltage cable was simulated using a three-phase voltage regulator,resistance wire,and wires,and the cable insulation aging was simulated by changing the resistance and capacitance values in parallel.Design and manufacture Rogowski coils,test their sensitivity and frequency characteristics and select the appropriate load resistance as the current transformer required for the test.The signal acquisition card is used to collect the electrical signals on the transformer,and the online monitoring system is programmed with Lab VIEW software.The Signal acquisition card is used to collect the voltage signal of CT two,and the on-line monitoring system is prepared by Lab VIEW software.In the laboratory,physical simulation experiment is carried out,the test results are verified by using the physical test model and the test result confirms the feasibility of the double differential CT method.