Harmonic Monitoring And Prediction Of Short Circuit Fault In Power Supply Network

Power supply network system is closely related to people's daily life,mainly including bus,transformer,transmission line and other power equipment.When the power supply network has a short-circuit fault and causes a power failure,it will have a serious impact on hospitals,stadiums,large shopping malls and important first-class equipment.Therefore,in the event of power failure,it is necessary to provide uninterrupted power supply for such first-class equipment quickly.Intelligent swift emergency power system(ISPs)is a new type of power supply which retains the advantages of UPS power supply and EPS power supply and improves their disadvantages.This paper mainly studies the fast detection method of ISPs power supply based on the short circuit fault of power supply network.The conventional detection method is mainly through the detection of the city power drop to judge.When there is a short circuit fault somewhere in the power supply system,the circuit breaker of this level must first cut off the power supply and enter the process of voltage drop(the response time of the whole process can reach 100ms),the ISPs power supply can enter the detection stage.In order to improve the detection speed and avoid the response time of circuit breaker,a method of detecting the harmonic content of fault signal is proposed.In this paper,the short-circuit fault of the power supply network is analyzed theoretically.Based on the theoretical analysis and the parameters of the actual power supply network,the simulation model of the power supply system is built by using MATLAB / Simulink.Through the simulation analysis of various faults in different locations,the harmonics with obvious increment change are found out.In order to detect the harmonic change accurately and quickly,FFT analysis and STFT analysis are used in this paper.FFT method can analyze the harmonic content of the signal in the detection section,and STFT method can observe the data from timefrequency domain.The advantages of both methods meet this requirement.Through theoretical analysis,MATLAB / Simulink modeling and simulation,FFT analysis and STFT analysis,the harmonic signal with obvious increment can be detected in 20 ms.According to the analysis,in most cases,the content of 0-th harmonic generally increases sharply,in some cases,the content of 15-th harmonic increases sharply,and in a few cases,the content of 16-th harmonic increases sharply.Therefore,by detecting the harmonic increment,the fast detection can be carried out before the response of the circuit breaker is completed.Compared with the time required by the conventional detection method,the method in this paper can advance more than 100 Ms.In conclusion,it is feasible to use the harmonic analysis method,and when the fault occurs,the detection time is greatly shortened,and the fault can be predicted.