Free Expert Guides on Power Systems, Circuit Design & Electrical Troubleshooting

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

Method of EarthingWe connect all the points to be earthed to the earthing grid using corrosion-resistant mild steel rods, buried at least 600 mm below ground. If these rods cross a cable trench, road, underground pipework, or rail track, they should be at least 300 mm below the barrier.We use MS rods for connecting the earth grid below ground level and MS flats above ground. The connection between different earthing points and the earthing grid is called the riser. We use MS flats for the riser

What is Short Circuit Protection?Short circuit protection definitionShort circuit protection is an important safety measure to prevent damage or fire caused by short circuit in the circuit. Short circuit protection is usually achieved through protective devices in the circuit that are able to quickly cut off the current when a short circuit is detected to protect other components and personnel in the circuit.Working principleThe working principle of short-circuit protection is based on the conce

What is the Differential Protection of Transformers?Differential Protection DefinitionThe differential protection of transformer is an important relay protection method, which is used to detect the faults inside the transformer, such as winding short circuit, turn short circuit and so on. Differential protection determines whether there is a fault by comparing the difference in current on both sides of the transformer.Principle of differential protectionDifferential protection is based on a basi

What is a Backup Relay ?Backup Relay DefinitionA backup relay is an additional relay system that operates if the main relay fails, ensuring continued protection.Function of Backup RelayThe primary function of a backup relay is to trip the circuit breaker when the main relay fails.Reasons for Main Relay FailureMain relays can fail due to mechanical defects, power supply issues, or problems in the CT/PT circuits.Importance of Backup RelayBackup relays provide an extra layer of reliability, essenti

What is an Electromagnetic Relay ?Electromagnetic Relay DefinitionAn electromagnetic relay is a switch that uses an electromagnet to mechanically operate a switching operation, essential in various electrical protection systems.Operation PrinciplesThe working of electromagnetic relays involves principles like magnitude and ratio measurement, essential for understanding their functionality in electrical systems.Types of Relays Attracted Armature type relay Induction Disc type relay Induction Cup

What is Protective Relay ?Protective Relay DefinitionA protective relay is an automatic device that senses abnormal conditions in electrical circuits and triggers actions to isolate faults.Types of Protective Relays Definite time relays Inverse time relays with definite minimum time(IDMT) Instantaneous relays IDMT with inst Stepped characteristic Programmed switches Voltage restraint over current relayOperating PrinciplesProtective relays operate by detecting abnormal signals, with specific pick

What is Differential Relay?Differential Relay DefinitionA differential relay is defined as a device that responds to the difference between two or more similar electrical quantities, such as currents or voltages, to detect faults.Principle of OperationThese relays activate based on discrepancies in electrical quantities within the protected zone, ensuring accurate fault detection.Types and ConfigurationsDifferential relays vary mainly into current and voltage balance types, each tailored for spe

What is an Instantaneous Relay ?Instantaneous Relay DefinitionAn instantaneous relay is defined as a relay that operates with no intentional delay when the current exceeds a set threshold.No Intentional DelayInstantaneous relays activate without any added delay, making them very fast in operation.Inherent DelaysThese relays still have minor delays due to electrical and mechanical factors, but they are not intentionally introduced.Types of Instantaneous RelaysExamples include attracted armature r

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