| Most of the faults that occur on the distribution network are short-circuit faults.After a short-circuit occurs,the line current increases and the voltage drops,which greatly affects the power quality and power supply reliability of the distribution network.After a fault occurs,after a certain period of time,the relay protection action is tripped.If the information after the fault can be used to locate the fault within an accurate range,the time required to find the fault can be greatly reduced,which is beneficial to the rapid recovery of power supply.The traditional fault location method is mostly based on the fault current monitored by the FTU on the distribution line,and the fault can only be located in the area enclosed by the FTU.If the phase voltage of each node on the low-voltage side of the distribution transformer is used for positioning,the fault can be located between several distribution transformers.This area is much smaller than the area enclosed by the FTU,which can effectively shorten time to find the fault location.In response to the above problem,this article has carried out the following research work:After the interphase short-circuit fault occurs on the medium-voltage side of the distribution line,the relay protection will act on a trip within a certain period of time.By collecting the phase voltage waveforms on the low voltage side of the distribution transformer two cycles before the breaker trips,Fourier windowing is performed on the collected voltage to obtain the effective value of the fundamental wave,and studying the relationship between the line voltage on the medium-voltage side and the phase voltage on the low voltage side of the distribution transformers.The voltage change law of the low-voltage side phase voltage after the medium-voltage side fault is obtained.The line length between adjacent nodes is introduced,the fault location criterion based on the phase voltage on the low-voltage side of the distribution transformer is proposed,and the fault is located between several adjacent distribution transformers,so as to achieve fine positioning of the faulty section.PSCAD simulation software is used to build a simulation model,and the distribution transformer parameters,line loads,distribution line parameters and models are designed.Through a series of simulations,the influence of different fault types,different fault locations,different load capacity and different transition resistances on voltage changes along the line is analyzed.In addition,the practical factor of adding distributed power sources of different capacities before and after the faulty node is also considered.The trend of voltage changes along the line of each node under the above-mentioned various conditions is obtained,and the feasibility of the fault location criterion based on the low-voltage side phase voltage proposed in this paper is verified.Combined with two typical cases,that is,when the fault resistance is large,the distributed generation capacity is large,the load capacity is light and the distribution lines are various,the voltage criterion proposed in this paper can still accurately locate the fault section,which proves the feasibility and effectiveness of the criterion proposed in this paper. |
