Protection Principles and Components

Protection Principles and Components:

Components of Protection System : Some of the more commonly used Components of Protection System are Relays Circuit Breakers Tripping and Other Auxiliary Supplies Current Transformer (CT) Voltage Transformers (VT) Linear Coupler Relays: The main function of a protective relay is to isolate a faulty section with the least interruption to service by controlling the circuit breaker, when abnormal conditions develop. Thus the relays may be designed to detect and to measure abnormal conditions and close the contacts in the tripping circuit. The following two categories of relays are most commonly used in protective relaying: Secondary indirect-acting relays: a group including practically all kinds of relays, e.g. current, voltage, power, impedance, reactance and frequency, whether minimum or maximum. Secondary direct-acting relays: a group of overcurrent and under-voltage relays designed to operate instantaneously or with time lag. These are primarily relays of the electromagnetic type which are built into circuit breaker operating mechanisms. Protection Principles and Components …


Derivation of Single Phase Quantity from Three Phase System : It will be seen later that auxiliary channels or pilot wires are used to transmit information from one end of the line to the other end. For a normal three-phase system three pilots would ordinarily be required which would obviously be a very costly affair for longer systems, particularly transmission circuits. It would naturally be preferable to have a means of deriving a single-phase quantity which under both normal and abnormal conditions will be representative of the three-phase conditions. Sometimes it becomes necessary to segregate the sequence currents or voltages from corresponding line currents or voltages in order to simplify the protection scheme by reducing the number of relays required. There are two commonly used methods for Derivation of Single Phase Quantity from Three Phase System (a) Summation Transformers: The three line current transformers (CTs) are connected to the primary of an auxiliary …


Methods of Discrimination in Power System Protection : Methods of Discrimination in Power System Protection are basically of two types: those which discriminate as to the location of fault, and those which discriminate as to the type of fault. Methods Discriminative to Fault Location: The main aim is that the faulty section of the system be isolated and in the minimum time. The various methods under this category are those in which the behavior of the protective apparatus is dependent upon where it is situated in the system relative to the point of fault occurrence. (a) Discrimination by Time: By adding time lag features to the controlling relays of a number of circuit breakers it is possible to trip the breaker nearest the fault prior to those farther off the point of fault. This simple scheme may be applied in a radial feeder shown in Fig. (2.1). The breakers at A, B, C and .D are identical …


Updated: May 1, 2020 — 5:02 pm