Pick Up Current | Current Setting | Plug Setting Multiplier and Time Setting Multiplier of Relay

During study of electrical protective relays, some special terms are frequently used. For proper understanding, the functions of different protective relays, the definition of such terms must be understood properly. Such terms are, Pick up current. Current setting. Plug setting multiplier (PSM). Time setting multiplier (TSM). Pick Up Current of Relay In all electrical relays, … Read more

Induction Cup Relay Working Principle Construction and Types

Induction Cup Relay This relay in nothing but one version of induction disc relay. Induction cup relay work in same principle of induction disc relay. The basis construction of this relay is just like four poles or eight pole induction motor. The number of poles in the protective relay depends upon the number of winding … Read more

Over Current Relay Working Principle Types

In an over current relay or o/c relay the actuating quantity is only current. There is only one current operated element in the relay, no voltage coil etc. are required to construct this protective relay. Working Principle of Over Current Relay In an over current relay, there would be essentially a current coil. When normal … Read more

Thermal Relay Working Principle Construction of Thermal Overload Relay

The coefficient of expansion is one of the basic properties of any material. Two different metals always have different degree of linear expansion. A bimetallic strip always bends when it heated up, due to this inequality of linear expansion of two different metals. Working Principle of Thermal Relay A thermal relay works depending upon the … Read more

Distance Relay or Impedance Relay Working Principle Types

There is one type of relay which functions depending upon the distance of fault in the line. More specifically, the relay operates depending upon the impedance between the point of fault and the point where relay is installed. These relays are known as distance relay or impedance relay. Working Principle of Distance or Impedance Relay … Read more

Instantaneous Relay

In a simple way electrical relay is shown in the figure above. Here the fixed coil is fed from the circuit to be protected. When there is a current in fixed coil above the pick up value, the iron plunger is so attracted, it moves upward and makes NO contact closed. The function of this … Read more

Inverse Time Relay | Definite Time Lag Relay

In this type of relays, the time of operation depends upon the magnitude of actuating quantity. If the magnitude of actuating quantity is very high, the relay operation is very fast. In other words, the relay operating time that is time delay in the relay is inversely proportional to the magnitude of actuating quantity. The … Read more

Differential Relay

The relays used in power system protection are of different types. Among them differential relay is very commonly used relay for protecting transformers and generators from localised faults. Differential relays are very sensitive to the faults occurred within the zone of protection but they are least sensitive to the faults that occur outside the protected … Read more

Feeder Protection Relays

Distance Protection Relay One of the important protections in Power System Protection is Feeder Protection. Different types of relays are used for feeder protection like electromagnetic type relays, static type relays etc. But now a day we are using Numerical relays for all protections. The benefits of Numerical relays are, Accurate tripping, Less tolerance, Fault … Read more

Motor Protection Relay for High Voltage Induction Motor

Above 90% of motors used in an industry are induction motors, because they are cheap, robust and easy to maintain. For higher HP (>250HP) motors we prefer high voltage, because it will reduce operating current and the size of the motor. Why We Require Protection of Motors? To understand this we need to know the … Read more