Transient analysis for ground fault distance estimation in electrical distribution networks.

摘要

The composition of ground fault transients, i.e. charge, discharge and interline compensating components, is first discussed. For transient analysis, a new two frequency model is introduced, which takes into account the interdependence of charge and discharge components. Of the various factors affecting the transients, fault resistance and loads were found to be the most important ones. When the magnitude of these is increased, the transients become damped, which makes their parameter identification difficult. Load impedances can also cause large errors to the distance estimates, although the parameters were identified accurately. Also errors of measurement transformers are discussed, and models proposed for the analysis of their transient response. From the other error sources, the effect of fault are nonlinearity was studied using a simulation model. Of crucial importance are the methods, by which the transient parameters are identified from the measured signals. In the prototype system developed, other signal components, except the charge transient, are first filtered out numerically. The transient parameters are then estimated using a least squares modification of Prony's method. Three methods were developed for fault location. The first one is based on the correlation of transient frequency and fault distance. The other two methods are based on the transient line terminal impedance. The measurements needed are from the phase voltages and phase currents of the faulty line. Finally other transient based methods, differential-equation algorithms and frequency domain methods, are discussed for comparison.