Gen diff protection: grounding connection on CT secondary

[PAP]

Hi all,
I have a question of installation of CT link to differential protection relay, please see attached file.
The problem is secondary CT connection was connect to ground oppose to generator terminal on both side which normal scheme will connect to ground on generator terminal side. (it could be better to see attached file)
So can I use this scheme for 87 protection? and are there any effect to the circuit or relay operation?

Thanks for helps.
Psit

 

[slavag]

Hi.
NO effect to the relay operation.
Diff current is still =0.
Regards.
Slava

 

[Sideswiper]

What sort of differential relay are you using?

I ask because maybe the relay (if it's digital) has a setting where you can change the polarity of the currents you are reading?

I'm not as familiar with the electromechanical... I would think you'd have to have your CT coils wired correctly to make them work properly.

 

[slavag]

grounding of star poin dosen't impact on the protection functionality ( maybe some special relays) . In diff relay important only one: or both star of CT's to protected object or both of them in opposite to protected object. If possible change it by setting is OK, if not only swap of one CT's set is needed.

 

[davidbeach]

Not great practice but the relay won't care. Normally a differential compares current into the zone from both ends; now you are comparing current out of the zone at both ends. The net effect is no change in operation. Depending on the nature of the relay you may have one too many grounds; if the two windings connect internally you need to verify that you have only one ground for any path. If the two windings are electrically independent you are fine with grounds as shown.