Research On On-line Insulation Monitoring And Fault Line Selection Method Of Distribution Network

With the rapid development of cities in my country,the capacity of the distribution network has also increased.In order to meet the requirements of power supply safety and aesthetics,cables are widely used in distribution network systems.The cable is buried deep underground and works in a complex environment,which will lead to the aging of the cable insulation in the electromagnetic environment caused by high voltage.Ground faults can also be caused by breakdown of the cable insulation or by external damaging factors during prolonged operation.The traditional manual inspection is inefficient,and it is difficult to detect insulation faults in time.With the development of science and technology,smart grid is the future development direction.The use of intelligent monitoring equipment can replace the traditional line inspection by personnel.It is of great significance to conduct online insulation monitoring and fault line selection research for distribution networks.This paper first describes the research background and significance of insulation monitoring and fault line selection,as well as the research status at home and abroad.This paper introduces the development of neutral point grounding methods in distribution network,summarizes and analyzes the existing methods of insulation monitoring and fault line selection,compares their advantages and disadvantages,and proposes the online monitoring method in this paper.In this paper,the signal injection method is selected as the basic method,starting from the equivalent model analysis of the cable,the overall circuit model is established from the equivalent model of the distribution network and the cable,and the ungrounded neutral point and the grounded system through the arc suppression coil are analyzed separately.This paper realized the theoretical algorithm of insulation monitoring and fault line selection.The frequency selection of injected signals and the All Phase Fast Fourier Transformation(APFFT)algorithm for extracting injected signals are analyzed.The simulation model of 10 kV distribution network is established in Simulink,and the simulation of insulation monitoring and fault line selection is carried out under different grounding methods to verify the online monitoring method proposed in this paper.The insulation monitoring simulation compares the injection signal and the power frequency signal,and verifies that the injection signal can still monitor the insulation state of the distribution network when the arc suppression coil is running online.The fault line selection simulation compares the traditional injection method and the method in this paper.The simulation is carried out under the conditions of different grounding resistances and different grounding positions.The method in this paper can effectively realize the fault line selection and has strong anti-interference ability.In order to carry out further simulation experiments,experimental devices such as on-line monitoring device for distribution network insulation were designed and developed.Considering that the distribution network cannot be tested under fault conditions for a long time,a 380 V three-phase distribution network system is built in the laboratory to simulate the real operation of the distribution network.A long-term online experiment was carried out in the simulated distribution network,and the insulation parameters of the cable were changed many times to verify the insulation monitoring method in this paper.And under the premise of ensuring safety,singlephase grounding is simulated by high-power resistance,and fault line selection experiments are carried out in different distribution network structures.Through simulation and laboratory simulation data analysis,the effectiveness and reliability of the method proposed in this paper for insulation monitoring and fault line selection of distribution network are verified.