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

What is a Dry Contact?A dry contact (also known as a volt free contact or potential-free contact) is defined as a contact in which power/voltage is not directly provided from the switch but is instead always being supplied by another source. Dry contacts are known as passive contacts, as no energy is applied to the contacts.Dry contact simply operates like an ordinary switch that opens or closes the circuit. When the contacts are closed the current flows through the contacts and when the contac

What is a Latching Relay?A latching relay (also known as a bistable, keep, impulse, stay relay, or simply a “latch”) is defined as a two-positional electromechanical switch. It is an electrically actuated switch used to maintain its position without power applied to the coil.A latching relay is used to control the large flow of current with a smaller current. The coil of the latching relay consumes power only while the relay is switched ON. And its contact remains in position after the switch

A feeder protection relay is a device that protects power system feeders from various types of faults, such as short circuits, overloads, ground faults, and broken conductors. A feeder is a transmission or distribution line that carries power from a substation to the load or another substation. Feeder protection relays are essential for ensuring the reliability and security of power systems, as they can quickly detect and isolate faults, prevent damage to equipment, and minimize power outages.Wh

There are different contacts connected in series along a trip circuit of an electrical circuit breaker. There must be some situation when the circuit breaker should not trip even a faulty current passes through its power contacts. Such situations are low gas pressure in SF6 circuit breaker, low air pressure in pneumatic operated circuit breaker etc. In this situation the trip coil of the CB must not be energized to trip the CB. So there must be NO contacts associated with gas pressure and air pr

For understanding motor thermal overload protection in induction motor we can discuss the operating principle of three phase induction motor. There is one cylindrical stator and a three phase winding is symmetrically distributed in the inner periphery of the stator. Due to such symmetrical distribution, when three phase power supply is applied to the stator winding, a rotating magnetic field is produced. This field rotates at synchronous speed. The rotor is created in induction motor mainly by n

There are different kinds of transformers such as two winding or three winding electrical power transformers, auto transformer, regulating transformers, earthing transformers, rectifier transformers etc. Different transformers demand different schemes of transformer protection depending upon their importance, winding connections, earthing methods and mode of operation etc.It is common practice to provide Buchholz relay protection to all 0.5 MVA and above transformers. While for all small size di

Before applying proper electrical protection system, it is necessary to have through knowledge of the conditions of electrical power system during faults. The knowledge of electrical fault condition is required to deploy proper different protective relays in different locations of electrical power system.Information regarding values of maximum and minimum fault currents, voltages under those faults in magnitude and phase relation with respect to the currents at different parts of power system, t

This portion of our website covers almost everything related to protection system in power system including standard lead and device numbers, mode of connections at terminal strips, color codes in multi-core cables, Dos and Don’ts in execution. It also covers principles of various power system protection relays and schemes including special power system protection schemes like differential relays, restricted earth fault protection, directional relays and distance relays etc. The details of trans

Over Current and Earth Fault Protection of TransformerBackup protection of electrical transformer is simple Over Current and Earth Fault protection are applied against external short circuit and excessive over loads. 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.The over current relays can not distinguish between external short circuit, over lo

It is essential to protect high capacity transformers against external and internal electrical faults.External Faults in Power TransformerExternal Short Circuit of Power TransformerThe short – circuit may occur in two or three phases of electrical power system. The level of fault current is always high enough. It depends upon the voltage which has been short-circuited and upon the impedance of the circuit up to the fault point. The copper loss of the fault feeding transformer is abruptly increas