Abstract:

The insulation monitoring and fault branch location are the key problems of substation DC system.To deal with the shortcomings of the detection methods such as pull circuit and balanced bridge,a comprehensive method relating to unbalanced bridge and wavelet transform is proposed.By monitoring the insulation of busbars to the ground with an unbalanced bridge,this paper presents a method which combines bus voltage deviation rate and detection sensitivity to ground.The optimal wavelet basis function is selected to filter and reconstruct the branch current,and the complex wavelet transform is used to extract the amplitude and phase information of the signal to calculate the grounding resistance,so as to complete the location of the fault branch.The simulation results show that the proposed method has higher detection accuracy with regard to the Fourier analysis method,and can restrain the influence of the distributed capacitance of the system to a great extent.

Key words: DC system, ground fault detection, unbalanced bridge, wavelet transform