How does a 87 differential relay work?

Published by Anaya Cole on

How does a 87 differential relay work?

Current differential relays typically are equipped with restraint windings to which the CT inputs are to be connected. For electromechanical 87 current differential relays, the current through the restraint windings for each phase is summed and the sum is directed through an operating winding.

What is a protection relay used for?

In electrical engineering, a protective relay is a relay device designed to trip a circuit breaker when a fault is detected.

What are the types of protective relay?

Types of Protective Relay

  • Electromagnetic Relays: Armature. Induction cup / induction disc.
  • Static Relays: Analog input signals are processed by solid state devices.
  • Digital / Numerical Relays: Uses programmable solid state devices based on digital signal processing.

What is an 86 trip?

Master trip relay or lockout relay, also known by ANSI code 86, holds a significant position as an intermediator between the protection relay and control points, even though it is not self-equipped with fault sensing capabilities.

What is an 87 relay fault?

This incorrect difference in currents will be seen by the 87 relay. Winding-to-winding fault: in this kind of fault some of the current from one winding escapes and enters the other winding at a 1:1 ratio. This effectively skews the transformer’s step-ratio, which imbalances the currents seen by the 87 relay.

Where does the differential protection relay receive current from?

Should a fault occur inside the zone of relay protection (that is between the CT’s), the differential relay would receive current in the operating coil. The example differential protection relay shown in the below figure is a transformer differential relay.

What is the zone of protection of a protective relay?

An important concept in protective relaying is the zone of protection. A zone of protection is the area that a given protective relay and/or overcurrent device (s) are to protect.

What is a digital protective relay?

Digital protective relays offer much more sophisticated approaches to the problem of false tripping based on mismatches between current transformer pairs and/or harmonic currents. The following graph shows the characteristic for a General Electric model 745 transformer protective relay providing differential current protection:

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