Relay Protection

Vinodh, I will tell you I work with low voltage (24VDC usually). Your question is not the sort of thing I know much about, but I often use a question from CR4 to further add bits to my own understanding and general knowledge base.

A google search finds a General Electric™ Application Guide to SPD and SPA relays. The information there is very informative for me, perhaps it will enlighten you.

The guide will make it clear to you "Whether pilot wire is applicable for any type of protection?", as it did for me.

Nice reply.

I was going to ask about the context but you answered that one too.

The GE SPD and SPA relays were older, static (electronic rather than electromechanical) pilot-wire transmission line protection relays. Doorman is correct in directing you to GE's link for information. They are used when a communication-assisted high-speed trip scheme is needed.

These relays have been pretty much superseded by digital, microprocessor-based relays from Schweitzer Engineering, NXT-Phase, ABB, and others (including GE) that give many more functions in the same box, with higher accuracy and reliability, and better user interface.

Thanks PeterT for the extra info. I would give you a GA for that.

As I said in my #2 post, I take more away from this forum than I put in. Thanks to you too, marcot.

Thank u friends.....i got it and found out that its not in practise nowadays due to the advencement in technology.