Instantaneous Overcurrent Relays: If the relay operates instantly without any intentional time delay, this characteristic can generally be satisfied by a relay of the non-polarized attracted armature type. This relay has a special advantage of reducing the time of operation to a minimum for faults very close to the source, where the fault current is […]
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Overcurrent Relay Characteristics: The operating time of all Overcurrent Relay Characteristics tends to become asymptotic to a definite minimum value with increase in the value of current. This is inherent in electromagnetic relays due to saturation of the magnetic circuit. So by varying the point of saturation different Overcurrent Relay Characteristics are obtained; these are:
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General Equation for Electromagnetic Relay: It has already been shown that when not more than two quantities are involved, the equation for the characteristic of the relay at the threshold of operation under steady state conditions, when plotted on complex planes is a circle. The General Equation for Electromagnetic Relay can be represented in a
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Comparator Equation in Power System Protection: Comparator Equation in Power System Protection – Taking a very general case to cover the complete range of conventional relay characteristics, let S1 and S2 be the two input signals such that when the phase relationship or magnitude relationship obeys predetermined threshold conditions, tripping is initiated. The input signals are
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Relay Design and Construction: The Relay Design and Construction is normally divided into the following stages: Selection of the operating characteristics. Selection of proper construction. Design of the contact movement from the point of view of utmost reliability. The relay operating characteristic must match with the abnormal operating characteristic of the system. In other words
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Induction Relay Torque Equation: In Induction Relay Torque Equation, Two magnetic fluxes Φ1 and Φ2 differing in time phase penetrate through a disc. These alternating fluxes induce emfs e1 and e2 in the disc which lag their respective fluxes by 90°. These emfs lead to the flow of eddy currents i1 and i2. By the interaction of Φ1 with
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Types of Electromagnetic Relays: There are two principal Types of Electromagnetic Relays: Attracted armature type; and Induction type. (a) Attracted Armature Type: This includes plunger, hinged armature, balanced beam and moving iron polarized relays. These are the simplest type which respond to a.c. as well as d.c. Figure (3.1) illustrates these types of relays. All
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Relay Classification in Power System Protection: There are various types of Relay Classification in Power System Protection. Normally the actuating quantity is an electrical signal, although sometimes the actuating quantity may be pressure or temperature. The electrical type of protective relays can be classified in a number of ways. (1) According to the function in
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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
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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
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