Study On Adaptive Monitoring Technique For Single-Phase Earthed Fault In Substation Using Transient Traveling Wave

In order to improve the reliability of power supply, non-effectively earthed neutral is widely used in medium voltage distribution networks ranging from 3kV to 66kV in china. Just so the earthed current is too small to monitoring when the single-phase earthed fault occurs, therefore, it’s very difficult to find the faulty feeder and remove of fault. The single-phase earthed fault monitoring in distribution networks increasingly become a difficult problem of distribution automation. Although many kinds of methods of fault monitoring, especially the methods based on the transient information, were proposed, practices show that the methods based on the single principle didn’t meet the demand that faulty feeder was monitored reliability under any single-phase earthed fault circumstances. It is a trend to realize fault monitoring reliability by compromising reasonably the advantages of different methods. Therefore, a new method of fault monitoring based on the dominant transient frequency and traveling wave is presented in the paper, which combines the merits of principle of fault monitoring of dominant transient frequency and traveling wave. The main works are as follows:1) The whole transient process when the single-phase earthed fault occurs in resonant ground systems is analyzed in theory. The characteristics and influencing factors of the zero modal components of initial transient traveling current and the dominant transient frequency are summarized by simulating kinds of single-phase earthed fault.2) The basic principles of line monitoring respectively based on the dominant transient frequency and the initial transient traveling current are showed at detail. And on this basis a new method of fault monitoring based on the dominant transient frequency and the initial transient traveling current is presented. The basic thinking of monitoring is as below:monitor the maximum point of amplitude-frequency characteristic of zero modal voltage of bus, the method based on the initial transient traveling current theory is adaptively used if there is only a maximum point, otherwise the method based on the theory of dominant transient frequency is considered.3) The simulation model based on the distributed parameter is set up using EMTP-ATP software and the data processing and algorithmic programming are realized by MATLAB software. The reliability of the fault monitoring algorithm is proved by simulating kinds of single-phase earthed fault situations.4) A distributed plan of line monitoring in substation in small current neutral grounding system is proposed. The basic structures and advantages compared with the centralized construction are presented in detail.In a word, the method of line monitoring presented on paper can reliably identify the single-phase earthed fault in small current neutral grounding system and be easily integrated with protector. It provides a new idea for faulty line monitoring in small current neutral grounding system.