Rotor Earth Fault Protection of Alternator or Generator

The rotor of an alternator is wound by field winding. Any single earth fault occurring on the field winding or in the exciter circuit is not a big problem for the machine. But if more than one earth fault occur, there may be a chance of short circuiting between the faulty points on the winding. … 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

Stator Earth Fault Protection of Alternator

This is to be noted that, the star point or neutral point of stator winding of an alternator is grounded through an impedance to limit the ground fault current. Reduced ground fault current causes less damage to the stator core and winding during ground or earth fault. If the ground impedance is made quite high, … Read more

Loss of Field or Excitation Protection of Alternator or Generator

Loss of field or excitation can be caused in the generator due to excitation failure. In larger sized generator, energy for excitation is often taken from a separate auxiliary source or from a separately driven DC generator. The failure of auxiliary supply or failure of driving motor can also cause the loss of excitation in … Read more

Motor Protection Circuit Breaker or MPCB

Motor protection circuit breakers are a specialized type of electrical protection device that is designed specifically for electric motors, like their name implies. Electric motors have plenty of applications and are used to drive mechanical devices of all types, so it is very important to protect them adequately with MPCBs. The following are just a … Read more

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

Busbar Protection | Busbar Differential Protection Scheme

In early days only conventional over current relays were used for busbar protection. But it is desired that fault in any feeder or transformer connected to the busbar should not disturb busbar system. In viewing of this time setting of busbar protection relays are made lengthy. So when faults occurs on busbar itself, it takes … 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

Overvoltage Protection

There are always a chance of suffering an electrical power system from abnormal over voltages. These abnormal over voltages may be caused due to various reason such as, sudden interruption of heavy load, lightening impulses, switching impulses etc. These over voltage stresses may damage insulation of various equipments and insulators of the power system. Although, … 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