Westinghouse IQ-1000 II Ground Fault Protection - CBCT Required ?
Westinghouse IQ-1000 II Ground Fault Protection - CBCT Required ?
(OP)
An existing Westinghouse IQ-1000 II motor protection relay does not have a Core-Balance CT, however its Ground Fault trip element is enabled and set.
The manual states that ground fault detection requires an ''optional ground fault (zero sequence) transformer be installed''.
If only 3 phase CTs are installed, does the relay determine the ground fault current from the residual current of the three phase CTs ? Or will the relay ignore the ground fault setting because there is no core-balance CT connected ?
The manual states that ground fault detection requires an ''optional ground fault (zero sequence) transformer be installed''.
If only 3 phase CTs are installed, does the relay determine the ground fault current from the residual current of the three phase CTs ? Or will the relay ignore the ground fault setting because there is no core-balance CT connected ?





RE: Westinghouse IQ-1000 II Ground Fault Protection - CBCT Required ?
If your line CTs happen to match this ratio then you could probably use the earth fault input with the residual connection. I suppose you 'could' use it with a different line CT ratio, but the scaling would be off and possibly not sensitive enough if you have large ratio CTs.
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RE: Westinghouse IQ-1000 II Ground Fault Protection - CBCT Required ?
To prevent nuisance tripping on starting I will use a pickup E/F current of 250A and definite time delay of 0.15 sec.
RE: Westinghouse IQ-1000 II Ground Fault Protection - CBCT Required ?
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RE: Westinghouse IQ-1000 II Ground Fault Protection - CBCT Required ?
The relay isn't really designed to accommodate a residual connection. If it were then the CT ratio would be configurable. It is intended only for a ZSCT. I wouldn't have thought it was a big deal to allow the earth fault CT ratio to be adjustable, but who knows what the designer had in mind - probably making the customer buy a matching CT!
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If we learn from our mistakes I'm getting a great education!
RE: Westinghouse IQ-1000 II Ground Fault Protection - CBCT Required ?
"Dear future generations: Please accept our apologies. We were rolling drunk on petroleum."
— Kilgore Trout (via Kurt Vonnegut)
For the best use of Eng-Tips, please click here -> FAQ731-376: Eng-Tips.com Forum Policies