What is Protective Relay ?

What is Protective Relay ?

Protective Relay Definition

A 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 relay

Operating Principles

Protective relays operate by detecting abnormal signals, with specific pickup and reset levels to start or stop their action.

Application in Power Systems

Primary and backup protective relays are critical for continuous and safe operation of electrical power systems.

Failure Modes

Understanding common failures in protective relays helps enhance system reliability and prevent prolonged downtimes.

Note points

• The relays indicate above shall be provided on HV and LV.

• Fans failure and pumps failure alarms to be connected.

• No Buchholz relay for transformers below 500 KVA capacity.