17 Facts About Protective relay

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

In many cases a single microprocessor Protective relay provides functions that would take two or more electromechanical devices.

This, however is not important; the only significant condition for a Protective relay is its setting and the setting can be made to correspond to a ratio regardless of the component values over a wide range.

Several operating coils can be used to provide "bias" to the Protective relay, allowing the sensitivity of response in one circuit to be controlled by another.

Drop off current of the Protective relay is much lower than its operating value, and once reached the Protective relay will be reset in a reverse motion by the pressure of the control spring governed by the braking magnet.

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The world's first commercially available digital protective relay was introduced to the power industry in 1984 by Schweitzer Engineering Laboratories based in Pullman, Washington.

Each digital Protective relay can run self-test routines to confirm its readiness and alarm if a fault is detected.

Distinction between digital and numerical protection Protective relay rests on points of fine technical detail, and is rarely found in areas other than Protection.

For example, a relay including function 51 would be a timed overcurrent protective relay.

An overcurrent relay is a type of protective relay which operates when the load current exceeds a pickup value.

The DTOC Protective relay has been used extensively in the United Kingdom but its inherent issue of operating slower for faults closer to the source led to the development of the IDMT Protective relay.

Definite time over-current Protective relay is a Protective relay that operates after a definite period of time once the current exceeds the pickup value.

An instantaneous over-current Protective relay is an overcurrent Protective relay which has no intentional time delay for operation.

The contacts of the Protective relay are closed instantly when the current inside the Protective relay rises beyond the operational value.

An inverse-time over-current Protective relay is an overcurrent Protective relay which operates only when the magnitude of their operating current is inversely proportional to the magnitude of the energize quantities.

Directional Protective relay uses an additional polarizing source of voltage or current to determine the direction of a fault.

Synchronism checking Protective relay provides a contact closure when the frequency and phase of two sources are similar to within some tolerance margin.