Transient analysis for ground fault distance estimation in electrical distribution networks

Post fault transient analysis for single phase to ground fault distance estimation in electrical distribution networks is discussed. The networks are assumed to be radially operated, and the neutral either isolated or compensated. The composition of ground fault transients (charge, discharge, and interline compensating components) is discussed. For transient analysis, a two frequency model which takes into account the interdependence of charge and discharge components is introduced. According to the theory, the charge transient, which is primarily due to the voltage rise of the two fault free phases, is most suitable for fault location, since it is the lowest in frequency and in most cases also the largest in amplitude. 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. Of significance also is the fault moment. If the instantaneous voltage is zero, the transient amplitudes are smaller than that of the uncompensated fundamental frequency fault current. 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 arc nonlinearity was studied using a simulation model.