Relay pick up current

[Fazlay]

As far i know for a protection relay,
Pick up current (Min Trip Current) = CT ratio × PSM (plug setting)

According to this formula,For below information i got 68A pick up current. Is this correct?

 

[ScottyUK]

400A CT with a 0.85 plug setting would give 340A pickup.

 

[davidbeach]

Sorry Scotty, I gotta go with the 68A. This is a 5A secondary CT, CTR = 80. The setting would be in secondary amps, so 80 * 0.85 = 68A. At 400:1 I'd agree with your 340A.

 

[ScottyUK]

David - yes of course. Too long in the world of 1A CT's - don't see so many 5A's these days. Sorry Fazlay.

 

[Fazlay]

it's ok Mr.Scotty. 5A CT's are really rare these days compare to 1A CT

 

[davidbeach]

5A CTs are far from rare. I don’t think I’ve ever even seen a 1A CT. Another one of those ANSI v. IEC things.

 

[ScottyUK]

Still quite a few on legacy systems in the UK, not many on my plant though. No excuse though!