Research On Power Line Fault Diagnosis Technology Of Resonant Grounding System

In recent years,with the continuous expansion of distribution network scale and the widespread use of cables,the single-phase grounding fault current has gradually increased,and the resonant grounding mode has gradually become the mainstream of the neutral point operation mode of distribution network in China.When a single-phase grounding fault occurs in a feeder,the inductive current generated by the tuned arc suppression coil can compensate the capacitive current of the system and greatly reduce the fault current.The grounding arc can be extinguished by itself,which creates conditions for the system to continue live operation for a period of time and greatly improves the reliability of power supply.While the arc suppression coil reduces the fault current,it also makes the single-phase grounding faulted line identification and section location of the resonance grounding distribution network line,which is already difficult,more complex,and limits the development of the huge advantage of high reliability of power supply of the resonance grounding system.In line faulted line identification method,the application of traditional steady-state method is limited by weak fault steady-state electrical quantity;transient method is facing problems such as signal easily disturbed and difficult to accurately detect;injection method has defects such as weak signal,single frequency and complex control.By relying on the traditional relay protection algorithm,the fault indicator is misoperated and refused to move,which reduces the accuracy of the existing fault section location methods.It is very important to study an effective line fault diagnosis technology in complex field environment to ensure the safe operation of resonant grounding system.Facing the difficulties in practical application of existing schemes,this paper proposes a line fault diagnosis method for resonant grounding distribution network which is suitable for high resistance grounding.In this fault diagnosis method,faulted line identification belongs to injection method,which makes full use of the advantages of active injection signal and makes up for the shortcomings of other injection methods.Fault section location is an improved method of traditional matrix method,which improves the accuracy of fault detection of various distribution automation equipment and ensures the success rate of location.Firstly,the method of disturbance signal injection and extraction is introduced.Pre-tuned arc suppression coils are connected in series or in parallel to limit neutral point displacement overvoltage in normal operation of power grid,while power electronic switches are gradually used to quit the damping resistance quickly in fault state due to their rapid action.Aiming at the "pre-adjustable" are suppression coil with power electronic switch,the damping resistance can be withdrawn equivalently for a short time by controlling the working state of the power electronic switch to generate the disturbance voltage and current with rich frequency components.The perturbation signal is extracted by subtracting the adjacent integer wave containing the perturbation signal,which is equivalent to the method of extracting the non-linear filter to eliminate the periodic interference in the signal.Using the frequency response acquisition method based on power electronic disturbance technology,the zero sequence frequency response of feeder is obtained by calculating the disturbance voltage and current signals.Secondly,faulted line identification criteria are formed based on the phase-frequency characteristics of zero-sequence frequency response of feeders,and then faulted line identification is completed.Disturbance signals are injected into fault feeders by coding method,and disturbances are decoded and extracted in each FTU.and then the established faulted line identification criteria are used to judge whether there is a fault downstream of monitoring points.According to the FTU judgment results,the fault section location is realized by combining the traditional matrix method.Finally,in the actual distribution network simulation model,the validity of the fault diagnosis scheme is verified,and the working range of the protection scheme is established,and compared with the implementation effect of the existing literature schemes.At the same time,it is analyzed that the disturbance signal injection will not affect the normal operation of the arc suppression coil.A simulation experiment platform is built to verify the validity of the faulted line identification scheme.Theoretical research,simulation analysis and simulation experiments show that the proposed method can generate disturbance signals with controllable intensity and rich frequency components without affecting the normal operation of the arc suppression coil,and can accurately select the fault feeder and determine the fault section,which can be well tolerated by the transition resistance and still be guaranteed under the noise interference of a certain signal-to-noise ratio.