Research On Traveling Wave-Based Fault Location Schemes For Single-Phase-to-Earth Faults In Neutral Ineffectively Grounded Systems

The neutral ineffectively grounded system represents a typical scheme in MV power distribution networks. The advantages of this kind of system are highly reliability and small fault current when a single-phase-to-earth fault happened. Fault location in a neutral ineffectively grounded system when a single-phase-to-earth fault happened is a problem unsolved in the world. This thesis devotes to solving the fault location problem mentioned above. Due to the lines in a neutral ineffectively grounded system usually have many branches and with one-end-power-supply, the main research work of the thesis pays attention to the fault location problem of this kind of lines. The principal contents are as follows.An overview of many methods for fault location is presented. Among the fault location methods, the one-end traveling wave-based scheme is selected as the method for the fault location of a line with branches and one-end-power supply. By analysis the characteristic of the traveling wave reflected back from a discontinuity when moving along a line with branches, a new indirect traveling wave-based fault location scheme is presented which locates the fault section and fault point by the reflections.The scheme for fault location presented here needs to find out the reflections from the line discontinuities. It's uneasy to identify the reflections from the fault point and those from other line discontinuities, for the reflections from the fault point mix with those from other discontinuities such as the ends of the line branches. The traveling time of the reflections from the ends of the line branches can be known if the wave velocity and the line configuration are certain. The reflections can be checked out by wavelet packets, for the wavelet analysis can map the singularity of a signal and the wavelet packets can figure the high frequency signals better than the wavelet transforms, a scheme using wavelet packets to find out the reflected waves is established. The new fault location scheme here has two steps. First the fault section is made sure by several special reflections. A big matrix which is used to confirm the fault section needs to find out by an eigenmatrix, the data in an eigenmatrix are made of the normalized part energies of several special reflections fronts. On the base of the fault section known, the second step is to determine the fault point according to the most mutuality time of two special reflections. An analysis is made for the application of the traveling wave-based fault location scheme on a neutral ineffectively grounded system under some different conditions, such as different neutral grounded ways and different single-phase-to-earth faults. The scheme is suitable for different conditions, because only the transient traveling wave signals at the initial stage are used, and the signals and conditions at the latter stage of a single-phase-to-earth fault have no influence on the fault location scheme.