In this post we will be seeing , the Basic Concept of Overcurrent Protection, which includes, relay Characteristics, Relay Settings with Example.
What is an Overcurrent Relay?
- Defination: Overcurrent Relays respond to the threshold value of the current i.e. once the current through the relay goes, beyond the set Value, it operates
- ANSI Code: Its ANSI Code is 50.
EHV system is an Interconnected Network System of Circuit Element, having more than one Voltage Source. Hence the Fault current may flow to Fault point from both end of any meshed line element. Hence, simple Overcurrent Relays cannot provide proper Co-ordination and Discrimination for Meshed Transmission System.
Input to the Overcurrent Relay is Current (fed through CT) and Output is the Trip Command to the Master Trip Relay or the Breaker.
It has a Current Setting (PSM) which is the Actuating Quantity controlling the Operation of the Relay and Time Setting (TMS), which controls Operating Time of the Relay.
When the Relay Operates, it gives Trip Signal to the Master Trip Relay or directly to the Breaker.
What is Pick up of the Relay?
The value of the current at which the Relay Operates is called as Pickup Value of the Current. It is used in the terms of Plug Setting Multiplier.