What is a Thermal Relay?Thermal relay definitionA thermal relay is defined as a device that uses unequal expansion rates of metals in a bimetallic strip to detect overcurrent conditions.Working principleThermal relays work by heating a bimetallic strip, causing it to bend and close the normally open contact, which triggers the circuit breaker.Construction of thermal relayIt consists of a bimetallic strip, metal with different expansion coefficients, a heating coil and contacts.Technical paramete

What is a Dry Contact ?Dry Contact DefinitionA dry contact is defined as a switch that controls electrical circuits without supplying the power itself, relying on an external source.FunctionalityDry contacts operate by opening and closing circuits, providing essential isolation and safety in electrical systems.Dry vs. Wet ContactsDry contacts are used for isolation, while wet contacts use the same power source for control and power supply, lacking isolation features.Applications of Dry ContactsT

What is a Latching Relay ?Latching Relay DefinitionA latching relay is a type of relay that maintains its contact position without continuous power application, allowing for efficient control of circuits.Circuit DiagramThe latching relay circuit diagram shows how Button-1 and Button-2 control the energizing and de-energizing of the relay, respectively.Operation MechanismBy pressing Button-1, the relay is energized and remains so even after the button is released, until Button-2 is pressed.Effici

What is Transformer Protection ?Transformer DefinitionA transformer is an electrical device that transfers electrical energy between circuits through electromagnetic induction.Nature of Transformer Faults Over current due to overloads and external short circuits Terminal faults Winding fault Incipient faultsTransformer ProtectionTransformer protection schemes are essential to prevent damages from faults and include devices like Buchholz relays and differential protection systems.Common FaultsTra

What is Generator Protection?Generator Protection DefinitionGenerator protection is the process of safeguarding generators from various electrical, mechanical, and thermal stresses.Types of ProtectionProtective relays are used to detect both internal and external faults, ensuring comprehensive generator protection.Insulation Failure ProtectionLongitudinal differential protection and inter-turn fault protection are crucial for preventing phase-to-phase and phase-to-earth faults.Rotor Fault Detect

What is Differential Protection?Differential Protection DefinitionDifferential protection is a method used to clear internal faults in the stator winding of a generator or alternator.Current TransformersTwo sets of current transformers (CTs) are used, one on the line side and one on the neutral side, and their characteristics must match to avoid relay malfunctions.Stabilizing ResistorA stabilizing resistor in series with the relay prevents operation due to external faults or CT saturation.Percen

What is Overvoltage Protection ?Overvoltage Protection DefinitionOvervoltage protection is defined as measures taken to prevent electrical systems from damage due to excessive voltage levels.Causes of OvervoltageOvervoltages can be caused by lightning, switching operations, insulation failure, arcing ground, and resonance.Switching ImpulseWhen a no-load transmission line is suddenly switched on or off, it can create a transient overvoltage in the system.Lightning ImpulseLightning can cause very

Wiring method of motor open-phase protection

Electromagnetic RelayElectromagnetic relays are those relays which are operated by electromagnetic action. Modern electrical protection relays are mainly micro processor based, but still electromagnetic relay holds its place. It will take much longer time to replace all electromagnetic relays by micro processor based static relays. So before going through detail of protection relay system we should review the various types of electromagnetic relays.Electromagnetic Relay WorkingPractically all th

Definition of Protective RelayA relay is automatic device which senses an abnormal condition of electrical circuit and closes its contacts. These contacts in turns close and complete the circuit breaker trip coil circuit hence make the circuit breaker tripped for disconnecting the faulty portion of the electrical circuit from rest of the healthy circuit.Now let’s have a discussion on some terms related to protective relay.Pickup Level of Actuating Signal:The value of actuating quantity (voltage