Reach of Distance Relay: A distance relay is set to operate up to a particular value of impedance; for an impedance greater than this set value the relay should not operate. This impedance, or the corresponding distance is known as the Reach of Distance Relay. To convert primary impedance (impedance of the line referred to …
Fault Resistance Calculation: Fault Resistance Calculation consists of two components, the resistance of the are and the resistance of earth. The second component is present only when it involves an earth-fault. In such a case the resistance of earth would mean the resistance of fault path through the tower, tower footing resistance and earth return. …
Time Grading of Distance Relay: Two methods of Time Grading of Distance Relay are shown in Fig. (5.18). First Method is the distance time method at (a) has the operating time increasing steadily with increasing distance between the relay location and the fault. For coordination of relays on consecutive sections as shown in Fig. (5.18a) …
Principle of Distance Relaying: The Principle of Distance Relaying is governed by the ratio of voltage to current at the relay location and the operating time of the relay automatically increases with an increase of this ratio. Now the impedance or the reactance of the circuit between the relay and the fault is proportional to …
Directional Earth Fault Relay: In the case of Directional Earth Fault Relay the angular relationship of residual current and residual voltage is independent of the faulted phase and is governed only by the R/X ratio of the fault path. The current coil of the directional element is connected to detect current in the residual circuit …
Overcurrent Earth Fault Protection: Overcurrent Earth Fault Protection – Earth-fault protection can be provided with normal overcurrent relays, if the minimum earth-fault current is sufficient in magnitude. The magnitude of earth-fault current is usually low compared to the phase-fault currents because the fault impedance is much higher for earth-faults than for phase-faults. It also depends …
Overcurrent Protection of Feeders: Overcurrent relays offer the cheapest and the simplest protection for lines. The maximum load currents must be known to determine whether the ratio of the minimum fault current to maximum load current is high enough to enable simple overcurrent operated relays to be used successfully. This criterion is chosen in order …
Types of Feeder Protection Relay: A composite transmission system may use one or more of the following types of Feeder Protection Relay. Overcurrent Protection: This is of two types: (i) nondirectional time and current graded schemes; (ii) directional time and current graded schemes. Distance Protection: This uses high speed distance relays. Pilot Protection: This is …