## Working Principle of Relay Articles:

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 i2 and Φ2 with i1 a driving torque is produced. The currents i1 and i2 lag the voltages e1 and e2 by the impedance angle λ of the disc. Figure (3.6) shows the vector diagram. Let Therefore, the resultant torque is given by. Thus the induction relay is a sine comparator in …

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 the protective scheme, relays may be divided into Main relays Auxiliary relays and Signal relays. Main Relays: The main relays are the protective elements which respond to any change in the actuating quantity, e. g. current, voltage, power, etc. Auxiliary Relays: The auxiliary relays are those which are controlled by other …

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 it should clearly show the conditions for tripping under various abnormal operating conditions. The most important considerations in the Relay Design and Construction are reliability, simplicity of construction and circuitry. The Relay Design and Construction is divided into the following: Contacts; Bearings; Electromechanical design; and Terminations and housing. 1. Contacts: Contact performance is probably …

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 these relays have the same principle, that is, an electromagnetic force is produced by the magnetic flux which in turn is produced by the operating quantity. The electromagnetic force exerted on the moving element is proportional to the square of the flux in the air gap or the square …