| China’s low-and-medium voltage distribution grids adopt the neutral point ungrounded method,and use the arc extinguishing coil to compensate for the fault current,which has a high reliability of power supply.However,with the increase of grid capacity and cable line coverage,the system-to-ground capacitive current is increasing.When it exceeds the compensation capacity of the arc suppression coil,the grounding arc cannot be extinguished,resulting in arc overvoltage,which not only endangers the system insulation,but also may lead to safety accidents due to the step voltage.In recent years,the voltage arc extinguishing scheme based on grounding fault phase bus has been gradually expanded in engineering.When a single grounding fault occurs in the system,the fault phase bus is repeatedly metal grounded,so that the voltage at the fault point is clamped to a very small value,and the grounding arc can be effectively extinguished.This method does not need to consider the strength and characteristics of the system’s capacitive current to the ground,and there is no problem of compensation capacity and measurement accuracy,so the arc extinguishing effect is significant.Meanwhile,faults occurring on the line can be transferred to the interior of the transformer substation to avoid any risk to personal safety.Therefore,based on D-PMU and its wide area measurement system,this paper studied the fault location method of medium and low voltage distribution grid under the manual grounding and arc suppression method.Firstly,in view of the need to determine the fault phase before the operation of the transfer device,a fault phase selection method based on the phase voltage difference was proposed.Combining the change of the phase voltage with the transition resistance,the application range of the existing fault phase selection method was divided,which can avoid the influence of system parameter asymmetry and voltage transformer error.Secondly,in view of the problem of fault line selection after the operation of the transfer device,a fault line selection method based on the transient energy difference of a single line was proposed.Unlike the existing fault line selection research that generally uses the transient information of different lines at the same fault time,this method uses the zero-sequence current of the same line at different time to calculate,effectively avoiding the influence of data synchronization problems on the line selection results.On the basis of fault line selection,in order to solve the problems of insufficient measurement accuracy and poor data synchronization of the distribution grid,a fault zone identification method based on dynamic time warping distance was proposed.The zerosequence current after the grounding fault transferred was used to verify the polarity of the zerosequence CT,and the zero-sequence current before the grounding fault transferred was used to identify the fault zone.Then,combined with branch lines,a fault zone search strategy based on dynamic warping distance was proposed.The method does not require complete data synchronization and has a strong ability to resist synchronization errors.The fault-tolerant characteristic of the DTW algorithm itself can overcome the problem of low transformer sampling accuracy.On the basis of fault line selection,accurate identification of fault zone can provide technical support for the rapid action of power distribution automation devices,which is of great significance for achieving fault area isolation and improving the system’s continuous power supply capability.Aiming at the problems of imperfect time-domain measurement system of distribution grid and low accuracy of transformers,around the new D-PMU application scenarios,a precise fault location method based on the time difference of arrival of the fault traveling wave was proposed.Synthesize the fault traveling wave transmission process at the time of fault grounding and bus grounding,the time difference coefficient was defined to characterize the relative position relationship between each measuring point and the fault point,and the fault zone was identified based on the network topology.Furthermore,taking the measurement point at the end of the downstream section of the fault point as the reference point,the accurate location of the fault was calculated by using the travel wave arrival time difference and the zone distance between the upstream measurement point and the reference point of the fault.The method uses the fusion processing of the traveling wave arrival time of each phase line mode as the traveling wave arrival time of each measuring point,avoiding the phase mode conversion,and the positioning accuracy is not affected by the traveling wave speed and the distributed power source.The simulation positioning error does not exceed 30 m.Finally,the main research and conclusions were summarized,and the future research work was prospected. |
