The Study Of The DC Ground Fault Line Select And Accurate Fault Location

The safe and stable operation of power system is closely related to national economy and people’s life. DC system is an important part in power system control, protection and monitoring.The reliability of dc system is closely linked to power system security and stability., So the fault in DC system timely detected and find out is very necessary in daily grid work. It can directly reduce the economic loss. The monitoring in DC system, the accuracy of the testing instrument, the timely detection and location when ground fault happened are all essential in daily work. There are many kinds of DC system grounding fault detection methods and instruments apply in the actual daily work at present. Because of the simple and easy operation, the low frequency current injection method has been the most widely used. But in the daily testing, this method also exposed many shortcomings: low frequency current injection method is vulnerable to various interference generated in the operation of the power system, such as the larger earth capacitance, many kinds of harmonic and noise. These interferences directly affects the accuracy of detection. It cannot find grounding fault branch in some extreme cases. How to improve the detection accuracy, cope with the extreme situation When grounding fault arise, and the selection of DC grounding circuit and the location the fault point in dc system grounding fault detection are mainstream direction of the research in recent years.Based on the defects in low frequency signal injection method when it apply in daily work,this paper put several improvements on the algorithm, make it can deal with complex operation environment of multiple conditions. This paper use wavelet transform to extract and analysis signals in lines. On the problem of fault line selection in question, using the multi-objective optimization model process the data, accurate the wavelet analysis results and finally find the fault line. On the problem find the fault point, use signal correlate locate the signal modulus maxima and finally find the fault point. This paper fuse the wavelet transform and multi-target optimize or signal’s autocorrelation to fuse algorithm in order to improve the detection accuracy.This paper describe the DC system constitute in detail, the element in ground fault and the detriment when it happened. List the detect methods in DC system ground fault, analysis and contrast the merit and demerit among these methods and finally select the low frequency current injection as this paper’s basic detect method. Improve the algorithm aim at the weakness in this method in order to enhance the detect accuracy. Finally simulate the proposed method.Analysis the complexity environment in DC system and the interferences in lines. Realise the current signals constitute in lines. Simulate many different signals in matlab and use them toprocess and compare the algorithm.Wavelet transform is a subscience which is widely be used and it is also the basic method in dealing with signals in this paper. This paper list the classic wavelet function and model. Use difference wavelet transform anylisis the signal, choose the coif4 wavelet as wavelet basis. This wavelet basis analysis the signal, the signal cannot be distorted in the low frequency and high frequency and it also can extract the accurate data.Apply the multi-target optimize problem in ground fault line select. Give the multi-target optimize basic definition, eigenvalu andweight function’s computing method, the decision making preference effect. The experiment shows: use the multi-target optimize problem when dealing with the data, it can improve the accurate in choose the fault line. It’s this paper’s purpose of research.When find the ground fault line, use low pressure pulse injection method to location the fault point. After injecting the low pressure pulse into thr fault line, use capture card to find voltage signals. After wavelet transform, use the signal’s autocorrelation find the time, and then locate the dault point.Simulate the current signals and voltage signals in matlab. Analysis the signals, record the data carefully. Use the data to calculate and then find the fault line and locate the fault point more accuracy.