The Research Of Nonlinear Circuit Parameter Measurement Method Of Cable Insulation Under DAC Voltage

XLPE power cable has been widely used in urban power grid because of its excellent performance.But the water-tree aging problem has always been the important factor that affects the cable life.In order to ensure the secure and stable operation of the power grid,avoid unnecessary economic loss,it is particularly necessary to diagnose the XLPE power cable.Therefore,the diagnosis of water-tree aging for power cable is of great significance.Firstly,this paper carries out simulation analysis on dielectric loss testing which based on the domestic first set of the damped oscillation wave testing system developed by the Jiangsu Electric Power Company Research Institute and China Electric Power Research Institute.The testing system model is built by Multisim software.Respectively on the basis of long and short cable model,we can consider the influence of different factors on test results.From the simulation results,no matter for long or short cable model,the high voltage switch conduction resistance has little impact on the result,the effect of voltage divider is less and can be neglected in actual test.In damp environment,the effect of capacitance and leakage conductance of the reactor than dry is increased,and the effect for short cable model is more obvious.Considering the above factors,the testing error of short model can not be ignored.Secondly,based on the above analysis of the simulation results and error,this paper proposes the method that based on the insulation parameter.By using cable terminal voltage and response current of cable insulation,we can obtain the nonlinear parameter of aging insulation.The nonlinear equivalent circuit model of aging cable is built by LabVIEW software.On the base of cable terminal voltage and the response current of insulation,we can obtain the model parameters(including nonlinear capacitor,nonlinear conductance)by the generalized linear fitting method.Under the action of the standard sine excitation voltage,we can get the loss factor and loss current harmonic component by analyzing.The simulation results show that the method can accurately get the nonlinear fitting parameter of cable insulation with high accuracy and reliability.At the same time,the method is not affected by excitation source interference.Finally,considering the measurement precision problem of the above method in the actual detection,this paper proposes a kind of current transformer optimization design method.Within the Multisim software,this paper builds the external circuit composed of operational amplifiers and other electronic for compensating the error of current transformer.From simulation results,the method makes the ratio difference and angle difference of current transformer improved.The accuracy level of transformer increases from 0.5 to 0.2.It shows that the method is feasible.