Category: Protective Relays

Types of Protection

Types of Protection: When a fault occurs on any part of electric power system, it must be cleared quickly in order to avoid damage and/or interference with the rest of the system. It is a usual practice to divide the Types of Protection scheme into two classes viz. primary protection and back-up protection. 1. Primary […]

Translay System

Translay System: This system is the modified form of voltage-balance system. Although the principle of balanced (opposed) voltages is retained, it differs from the above voltage-balance system in that the balance or opposition is between voltages induced in the secondary coils wound on the relay magnets and not between the secondary voltages of the line […]

Differential Relay

Differential Relay: Most of the relays discussed so far relied on excess of current for their operation. Such relays are less sensitive because they cannot make correct distinction between heavy load conditions and minor fault conditions. In order to overcome this difficulty, differential relay are used. A differential relay is one that operates when the […]

Definite Distance Type Impedance Relay

Definite Distance Type Impedance Relay: Fig. 21.21 shows the schematic arrangement of a Definite Distance Type Impedance Relay. It consists of a pivoted beam F and two electromagnets energized respectively by a current and voltage transformer in the protected circuit. The armatures of the two electromagnets are mechanically coupled to the beam on the opposite […]

Distance Relays or Impedance Relays

Distance Relays or Impedance Relays: The operation of the relays discussed so far depended upon the magnitude of current or power in the protected circuit. However, there is another group of relays in which the operation is governed by the ratio of applied voltage to current in the protected circuit. Such relays are called Distance […]

Induction Type Directional Overcurrent Relay

Induction Type Directional Overcurrent Relay: The directional power relay is unsuitable for use as a directional protective relay under short-circuit conditions. When a short-circuit occurs, the system voltage falls to a low value and there may be insufficient torque developed in the relay to cause its operation. This difficulty is overcome in the Induction Type […]

Induction Type Directional Power Relay

Induction Type Directional Power Relay: This Induction Type Directional Power Relay operates when power in the circuit flows in a specific direction Unlike a non-directional overcurrent relay, a directional power relay is so designed that it obtains its operating torque by the interaction of magnetic fields derived from both voltage and current source of the […]

Induction Type Overcurrent Relay

Induction Type Overcurrent Relay(Non-Directional): This Induction Type Overcurrent Relay works on the induction principle and initiates corrective measures when current in the circuit exceeds the predetermined value. The actuating source is a current in the circuit supplied to the relay from a current transformer. These relays are used on a .c. circuits only and can […]

Relay Timing Circuit

Relay Timing Circuit: An important characteristic of a relay is its time of operation. By the Relay Timing Circuit of operation is meant length of the time from the instant when the actuating element is energized to the instant when the relay contacts are closed. Sometimes it is desirable and necessary to control the operating […]

Basic Relays

Basic Relays: Most of the Basic Relays used in the power system operate by virtue of the current and/or voltage supplied by current and voltage transformers connected in various combinations to the system element that is to be protected. Through the individual or relative changes in these two quantities, faults signal their presence, type and […]