Measured Impedance at Source Node of a Distribution Feeder

Distance relays are widely used in the protection of transmission systems. Main and backup protection of the transmission lines are provided by distance protection, which is based on the measured impedance at the relaying point. On the other hand, the protective systems in the case of distribution networks consist of over-current relays and fuses. Both the main and backup protections are provided by means of the over-current relays and fuses. Distance protection is not utilized in distribution networks, due to the inherent characteristic of the distribution networks and the additional required facilities of the distance protection, compared with over-current protection. The measured impedance at the relaying point plays a great role in satisfactorily operation of distance protection. In the case of zero fault resistance, the measured impedance at the relaying point is independent of the system conditions. But in the presence of the fault resistance, the measured impedance deviates from its actual value according to the network structural and operational conditions and specially the magnitude of the fault resistance. However, this paper studies the measured impedance at the source node of a distribution feeder. The tripping characteristic is presented for the distribution feeder. The variation of this tripping characteristic is studied as a function of the changes in the operational and structural conditions of the distribution system.

Keywords:

Distance relay , Distribution feeder , Fault resistance , Measured impedance , Tripping characteristic