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An overcurrent relay is a type of protective relay which operates when the load current exceeds a pickup value. It is of two types: instantaneous over current (IOC) relay and definite time overcurrent (DTOC) relay. The ANSI device number is 50 for an IOC relay or a DTOC relay. In a typical application, the over current relay is connected to a ...
Power system protection is a branch of electrical power engineering that deals with the protection of electrical power systems from faults [citation needed] through the disconnection of faulted parts from the rest of the electrical network. The objective of a protection scheme is to keep the power system stable by isolating only the components ...
Similarly, the "G" suffix can denote a "ground", hence a "51G" is a time overcurrent ground relay. The "G" suffix can also mean "generator", hence an "87G" is a Generator Differential Protective Relay while an "87T" is a Transformer Differential Protective Relay.
Possible causes for overcurrent include short circuits, excessive load, incorrect design, an arc fault, or a ground fault. Fuses, circuit breakers, and current limiters are commonly used overcurrent protection (OCP) mechanisms to control the risks. Circuit breakers, relays, and fuses protect circuit wiring from damage caused by overcurrent. [1]
An inrush current limiter is a device or devices combination used to limit inrush current. Passive resistive components such as resistors (with power dissipation drawback), or negative temperature coefficient (NTC) thermistors are simple options while the positive one (PTC) is used to limit max current afterward as the circuit has been operating (with cool-down time drawback on both).
In electronics and electrical engineering, a fuse is an electrical safety device that operates to provide overcurrent protection of an electrical circuit. Its essential component is a metal wire or strip that melts when too much current flows through it, thereby stopping or interrupting the current.
The relay analyzes the resultant A/D converter outputs to determine if action is required under its protection algorithm(s). Protection algorithms are a set of logic equations in part designed by the protection engineer, and in part designed by the relay manufacturer. The relay is capable of applying advanced logic.
Another way to avoid the transformer inrush current is a "transformer switching relay". This does not need time for cool down. It can also deal with power-line half-wave voltage dips and is short-circuit-proof. This technique is important for IEC 61000-4-11 tests. Another option, particularly for high-voltage circuits, is to use a pre-charge ...