Single-phase Disconnection Location Of Neutral Ungrounded System Based On Distribution Voltage Monitoring Information

Single-phase disconnection fault,as a common fault type in distribution network,will lead to problems such as poor power quality,influence of normal power supply,and easy to lead to safety accidents such as electric shock.It is very important for the safe operation of distribution network to locate the fault of single-phase disconnection,which is beneficial to the follow-up manual inspection and fault repair.Therefore,on the basis of in-depth analysis of the voltage characteristics of single-phase disconnection fault,this paper studies the localization method of single-phase disconnection fault.The theoretical analysis is made on the voltage characteristics of single-phase disconnection non-grounding fault,single-phase disconnection plus power side(metallic)grounding fault,single-phase disconnection plus load side(metallic)grounding fault and single-phase disconnection on one side and on both sides of single-phase disconnection grounding fault through transition resistance,and the variation law of voltage of upstream and downstream medium-voltage side line and low-voltage side voltage after fault is deduced.A 10kV ungrounded system simulation model was built based on PSCAD/EMTDC platform,and the correctness of theoretical analysis was verified.Through the grounding resistance,break the downstream side load,system of capacitance,bolt location and fault line capacitance accounted for the proportion of the total earth capacitance the influencing factors of fault voltage within the scope of their respective values such as random sampling scenario set structure,calculate the bolt downstream side voltage distribution probability.By combining theoretical analysis with simulation,the adaptability of ground resistance and load unbalance rate is studied,and the influence of three-phase and single-phase distributed power supply grid-connection on the voltage characteristics of disconnection fault is deduced.Combining with the simulation model of distributed power supply grid-connection disconnection,the capacity boundary conditions of distributed power supply that do not affect the voltage characteristics of disconnection fault are obtained through simulation.It is pointed out that the disconnection fault section can be located by using the voltage difference between the upstream and downstream low-voltage side of the fault location,and the disconnection fault criterion is constructed as follows:For distribution transformers connected with DYN11,the breakout section is between the abnormal point at the low-voltage side where the voltage of two phases is lower than 0.85 and the voltage of the other phase is higher than the threshold value of the high voltage detected nearest to the power side and its adjacent non-abnormal points.For the distribution transformer connected with YYnO,the disconnection section is between an abnormal point with a phase voltage lower than 0.85 on the low-voltage side detected nearest to the power side and its adjacent non-abnormal points.Using the phase voltage on the low voltage side of feeder information is given for single phase positioning bolt section steps.Combined with the actual case of a certain urban area,the disconnection area is correctly judged by using the two disconnection location criteria constructed in this paper.An example is given to verify the influence of DG on the disconnection location method in this paper,and the feasibility and effectiveness of the disconnection location method in the actual scene are verified.