Low Voltage Arc Fault Detection Method And Device

Low-voltage circuit breakers,fuses and other protective devices are commonly used in the low voltage power supply system.By detecting the current and residual current effective value,they can effectively prevent electrical faults,such as short circuit,over load and earth leakage.However,the arc fault caused by bad contact and insulation failure can not be effectively detected and reliably removed.At present,the fault arc detection products in foreign markets are not suitable for the power supply system in china,moreover,the accuracy and reliability of the test need to be further improved.In this paper,the detection method of series arc fault in low voltage power supply system is studied.Based on the simulation model and the simulation experiment,the current waveforms under different loads are collected.The frequency band for characterizing the fault characteristics and the corresponding wavelet basis function are optimized.Based on the wavelet high frequency component,the fault criterion is established,and the fault detection device is designed.The main research work and results are as follows:1.Based on the Cassie arc model,the series arc fault is simulated in AC power supply system,and the influence of arc voltage parameters on arc current and voltage waveform is studied.The fast Fourier transform of the fault current waveform is used to calculate the energy and energy ratio of each frequency band,the characteristic frequency band of arcing fault is obtained.2.According to the relevant national standards,the fault arc simulation experimental platform is set up,and the current waveforms of different loads under normal and various fault conditions are collected.The influence of the load current and the intensity of the arc burning on the series arc fault current waveform under resistive load is studied.The wavelet transform is used to analyze the fault current waveform,by comparing the energy ratio of the high frequency components,the wavelet basis function and the decomposition level are selected to extract the wavelet high frequency component.3.The statistical analysis of the high frequency component of the resistive load currentshows that the high frequency component index can accurately represent the series arc fault.On the basis of the above analysis,the wavelet high frequency component periodic variance index can be used to distinguish the normal and fault currents.The effectiveness of the method is proved by the results of several similar loads.4.On the basis of the research of the detection method,the low-voltage arc fault detection device is designed.The hardware circuit is composed of STM32 microcontroller,power supply and peripheral circuit,current transformer,current conditioning circuit,data acquisition chip,alarm and trip.The software design includes the main program and interrupt service program.