A protection relay is a device that senses any change in the signal it is receiving, usually from a current and/or voltage source. 4. If the magnitude of the incoming signal is outside a pre-set value the relay will carry out a specific operation, generally to close or open electrical contacts to initiate some further operation, for example the tripping of a circuit breaker. Polarization is the method used by the relay to determine the direction of current flow. Based on the structure, induction relays are classified as: Shaded Pole – Structured pole is generally activated by the flow of current in a single coil which is wounded on a magnetic structure that has an air gap. Distance relaying. Reverse power flow relays with directional features, not only senses the direction flow, but also measures magnitude of power flow. Moreover, impact of power flow direction at normal operation of the power system is considered in the evaluation of the algorithm. The differential current that will flow through the overcurrent relay may be sufficient for the relay to pick up and cause false tripping of the circuit breakers. Both fault currents flow into the transmission line, so the directional overcurrent relays connected to Circuit Breakers 3 and 4 will see the current in the forward direction because the current flows into both CT polarity marks. The choice of directional unit depends upon the type of comparator used. Directional relays are based on flow of power. 4. Directional relays are based on flow of (a) power (b) current (c) voltage wave (d) all of the above Ans: a. Draw a typical time-current characteristic for IDMT relay. A differential relay measures the vector difference between (a) two currents (b) two voltages (c) two or more similar electrical quantities (d) none of the above Ans: c. 26. According to the above, the directionality to the fault is identified based on two criteria; the directional current signal given in and the directional normal power before fault occurrence. 32Q solid-state directional relays. Directional Relays . In this paper, a high-speed current-based directional algorithm is presented. Sign of the summation and direction of power flow at normal condition determine fault direction. For a specified interval, the fault current samples are multiplied by corresponding prefault current samples and summation of the results is calculated as a criterion. Directional relays are based on the flow of. asked Jun 23 by anonymous. A. In electrical engineering, a protective relay is a relay device designed to trip a circuit breaker when a fault is detected. in order to get a proper and uninterrupted power the power system failure must be quickly determined and the failed part must be disconnected from the power system. ... A type of relaying which is responsive to the direction of the flow of power and line impedance is normally designed as. Numerical Relay Types: The following are the various types of numerical relays. This chapter concentrates on the application theory of directional distance relays, because they are the most essential relays and are widely applied for purposes such as detecting primary and backup faults in lines and equipment, detecting generator loss of excitation, detecting step‐outs, etc. Also, its performance is compared with some other directional algorithms. Standard overcurrent relays cannot distinguish the direction of the current flow. To protect these loads, circuit breakers and relays are required at appropriate places with proper coordination between them. 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