What is an Over Current Relay?Overcurrent Relay DefinitionAn overcurrent relay is a protective device that operates solely based on current without the need for a voltage coil.Working Principle of Over Current RelayThe core component of an overcurrent relay is a current coil. Under normal conditions, the coil’s magnetic effect is too weak to overcome the restraining force and move the relay’s element. However, if the current increases sufficiently, its magnetic effect intensifies, surpassing the

Varmeter circuit

What is Induction Cup Relay?Induction Cup RelayThis relay is a version of the induction disc relay. Induction cup relays work on the same principle as induction disc relays. The basic construction of this relay is similar to a four-pole or eight-pole induction motor. The number of poles in the protective relay depends on the number of windings needed. The figure shows a four-pole induction cup relay.When the disc of an induction relay is replaced by an aluminum cup, the inertia of the rotating s

Motor Thermal Overload Protection

Feeder Protection Relay DefinitionA feeder protection relay is defined as a device that protects power system feeders from faults like short circuits and overloads.It measures the feeder line’s impedance (Z) using voltage (V) and current (I) inputs from the potential transformer (PT) and current transformer (CT). Impedance is calculated by dividing voltage by current: Z = V/I.The relay compares the measured impedance to a preset value that represents the maximum allowable impedance for normal op

Trip circuit monitoring definitionTrip circuit monitoring relays are an essential system in circuit breakers to monitor and ensure the readiness and health of the trip circuit.ModsThe basic components of a monitoring circuit include NO and NC contacts, relays, lights, and resistors, all of which help maintain circuit integrity.Monitoring schemeA NC contact of the same auxiliary switch is connected to the auxiliary NO contact of the trip circuit. When CB is closed, the auxiliary NO contact is clo

Motor thermal overload protection setThermal overload protection is a safety mechanism that prevents the motor from overheating by detecting excessive current and stopping the motor.Cause of overheatingWhen considering motor overheating, the first cause that comes to mind is overload. Mechanical overload causes the motor to consume a higher current, which leads to overheating. If the rotor is locked by external forces, consuming too much current, the motor will also overheat. Low supply voltage

Electrical Fault Calculation DefinitionElectrical fault calculation involves determining the maximum and minimum fault currents and voltages at different points in a power system to design protective systems.Positive Sequence ImpedancePositive sequence impedance is the resistance faced by positive sequence current, crucial for calculating three-phase faults.Negative Sequence ImpedanceNegative sequence impedance is the resistance faced by negative sequence current, important for understanding unb

Power System Protection DefinitionPower system protection is defined as the methods and technologies used to detect and isolate faults in an electrical power system to prevent damage to other parts of the system.Circuit BreakersThese devices are crucial for automatically disconnecting the faulted part of the system, ensuring the stability and safety of the remaining electrical grid.Protection RelaysProtection relays monitor the electrical network and initiate the tripping of circuit breakers whe

Backup Protection These over current and earth Fault relays may be of Inverse Definite Minimum Time (IDMT) or Definite Time type relays (DMT). Generally IDMT relays are connected to the in-feed side of the transformer.Overcurrent relays cannot differentiate between external short circuits, overloads, and internal faults of the transformer. Backup protection, using overcurrent and earth fault protection on the in-feed side, will activate for any of these faults.Backup protection is usually instal