International Journal of Research and Scientific Innovation (IJRSI) |Volume III, Issue IX, September 2016|ISSN 2321–2705 www.rsisinternational.org Page 86 Transmission Line Trip Region for Single Line to Ground Fault in Various System Configuration and Operating Condition Rahul Sharma Assistant Professor Suresh Gyan Vihar University Jaipur, India Apoorva Singh B.E.(Electrical) Suresh Gyan Vihar University, Jaipur, India Abstract - The distance relays installed at substations continuously monitor the impedance. This impedance is called apparent impedance. During fault, the transmission line impedance restrict fault current, thus apparent impedance becomes transmission line impedance. This apparent impedance is significantly affected by fault resistance (tower footing resistance for SLG), prefault system conditions (i.e. load flow & voltage level), prefault system configuration (i.e. source impedance, in-feeds), shunt capacitance and mutual coupling of parallel lines. In this paper, the effects of all mentioned parameters are studied. I. INTRODUCTION istance protection is commonly used for protection of transmission lines. Out of various possible faults, the occurrence of single line to ground fault is very high. Till now, we have studied SLG fault under unloaded condition. However, ground fault resistance, remote end in feed, sources‟ impedance, system configuration, & present operating condition (Load flow) etc affect the reach accuracy of relay. Moreover, line capacitance and mutual coupling also affect reach accuracy of relay. For a simple two source equivalent system (Fig.1.1), the apparent impedance for SLG in phase A can be given by - Za=xZL+(1+IMF/INF).R F Fig 1 Two source equivalent system Hence, apparent impedance is not only dependent on fault location x but also remote end in feed along with fault resistance R F . R F is dependent on tower footing resistance which may vary up to 200Ω depending upon country soil characteristics. These parameters remain unknown though system operating condition i.e. remote end equivalent voltage and source impedance can be estimated with breaker status and made available to substation using SCADA. If system characteristic is fixed, Rf and x are only variables; then a trip region (Fig1.2) can be prepared. Fig 1.1 TRIP REGION 1. Distance Relay Over-current relays are very cheap and considerably reliable. Hence, they constitute very significant portion of LV industrial protection system. However, they suffer some major drawbacks. It is very difficult to implement coordination, selectivity [1]. The reach of over-currents relay is heavily depending upon the type of fault and source impedance. The source impedance is changing with switching on/off of lines. Hence, relay may overreach or under reach with change in system configuration and fault resistance. 1.1 Distance Relay Fundamentals Let us consider a single phase line MN, having a stiff source at location M and no source at location N. For simplicity line is modeled as R-L series circuit (i.e short line) as shown in Fig1.2 D