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Hi z bus Ct configuration

Hi z bus Ct configuration

Hi z bus Ct configuration

I've encountered a bus Ct application that I need some help wrapping my head around. Two breakers with 2000:5 contributions to PVD's. Hi side transformer ct's DO Not contribute directly, are 1200:5 and are wired in parallel to the 1200:5 taps on the BKR ct's.
I see this is necessary to accommodate the mis-match of ratios and I see what appears to be an auto transformer affect making this work but I need to be in tune to what all is working together here before I remove one Bkr from service completely while maintaining my bus protection. I'm lacking sufficient Ct engineering theory to reconcile this. Any advise shall be greatly appreciated and thanks in advance.

RE: Hi z bus Ct configuration


An AC schematic single line diagram would be a big help.


RE: Hi z bus Ct configuration

Aux CTs not a good idea for High Z bus differential, if that is what you are talking about.

RE: Hi z bus Ct configuration

Yes it is possible to use CTs of different ratios. See

SEL-587Z Relay Application With Multiratio Current Transformers
Application Guide - This application guide deals with incorporating mixed ratio current transformers in the protection scheme and obtaining a satisfactory operation of the relay with high security against external faults.

RE: Hi z bus Ct configuration

SLD or scheme is preferred to support you better.


RE: Hi z bus Ct configuration

Protectionengineer, Thanks, exactly what I needed and could not find myself on web.

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