Studies On Feeder Selection, Sectionalization And Location Of Single-phase Fault In Multi-Branch Distribution Network With Neutral Un-Effectively Grounded

Although faulty feeder selection methods in the case of single phase to ground fault in Neutral Un-effectively Grounded System (NUGS) has been studied for many years and a lot of research has been done, the performance of the existing methods is still unsatisfactory. Furthermore, adequate solutions for direct faulty section identification and accurate location in the condition of this fault have not been available, especially for the distribution network with the neutral point grounded via arc suppression coil (also known as Peterson coil). Involvement of the arc suppression coil may decrease short-circuit current, but the difficulty of finding fault location is increased. The key problems of non-solid single-phase to ground fault location lie in these three aspects:faulty feeder selection, faulty section identification and fault location.To highlight the difference of the zero sequence admittances between the faulty feeder and the sound feeder, a zero sequence compensated admittance method is introduced. In this way, the setting of the criterion becomes feasible and the on-site requirement to the protection has also been involved. A variety of simulation tests were carried out by virtue of ATP software. The results demonstrate that this algorithm is immune to the variation of network structures and parameters, fault conditions, and fault resistance etc. The successful rate of feeder selection is proved to be improved to a great extent.One of the aspects of this dissertation is to analyze line capacitive current distribution of isolated neutral point and neutral point grounded via arc suppression coil. On this basis, three methods to identify the faulty section of the feeder in a multi-branch distribution network are proposed, that is, per-unit zero sequence current method, medium resistance switching-on/off based method and transient current distribution based method. All of three mentioned method can provide satisfying results on which fault section can be identified. Simulation studies using PSCAD/EMTDC software are carried out to verify the effectiveness of these methods.Furthermore, a novel single-ended traveling wave based fault location method applicable to the distribution network with multiple branches is presented. The method only depends on the arrival times of the initial aerial-mode and zero-mode travelling wave, and it is not affected by structure of a distribution network itself. Therefore, good results can be achieved for accurate fault locating in multi-source and multi-branch distribution networks. In addition, the impacts of different factors on the fault location accuracy are investigated. The feasibility and effectiveness of this method is also verified by PSCAD/EMTDC simulation results.