Core Balance CT
Core Balance CT
(OP)
Is there a difference between Core Balance CT for ground fault detection and a phase CT used for o/c protection?
I understand for ground fault detection, you have to run all three phase conductors through the CT but does it require a special window type CT?
I understand for ground fault detection, you have to run all three phase conductors through the CT but does it require a special window type CT?






RE: Core Balance CT
RE: Core Balance CT
RE: Core Balance CT
I am having a difficult time locating a suitable ct.
RE: Core Balance CT
RE: Core Balance CT
GE/ITI, Link
ABB, Link
Schneider Electric, Link
RE: Core Balance CT
Even with a zsct you still have to choose the appropriate window size / burden and ratio.
Am I missing something here?
RE: Core Balance CT
Core Balance CT
Ground Fault CT
Zero Sequence CT
Window CT
These names does not implied how a CT is constructed because they are all the same phsyically (other than ratio, accuracy, burden and window size).
The name only tells you how a CT is applied, in this case the first three names are for ground fault detection and the last name is for phase current detection.
If a window CT has all phase conductors going through it and its used with a ground fault relay, then we can it CBCT, ZSCT or Ground Fault CT?
Is that correct?
RE: Core Balance CT
RE: Core Balance CT
rasevskii
RE: Core Balance CT
I cannot speak for all CT makers but I can speak for those that I have personally been involved with - with regards to zero sequence GF CTs they are wound in a different manner than a typical CT. In ZSGF all three phases pass thru the window, and it is possible to have unequal line currents that balance in the neutral, and since placement of those conductors may or may not be controlled, the winding must be structured such to prevent nuisance tripping. This is typically true of low ratio units (50/5, 100/5). So due to the unequal line currents you will have unequal flux entering the core at different sections of the core. Depending on the sensitivity it can create issues.
Further, depending on the window size and shape, not all cores will be same. Some may be continous tape wound (toroidal or oblong) and others may be stacked laminations (real long windows). So my suggestion when using a single core for zero sequence apps (core balance CT), specifiy the application as such.
From my perspective, core balance and zero sequenece have same meaning. GF may or may not be the same. BUT they all can be window-type CT.
RE: Core Balance CT
Can you please explain more by what you meant on your post below?
When using core balane CTs it is important that the cable sheath (armor) conductor passes backward through the CT window to its ground bus connection. THis to avoid sheath currents from causing a false operation of the protection. Cable sheath currents can be caused by third harmonic currents originating from generators connected to the busbars ( a typical Diesel Powerplant method) rather than via individual transformers.
What does "passes backward through the CT window" mean? If you have a drawing/ circuit diagram to illustrate, please share. We are encountering some false operation of protection and would like some ideas. Thanks in advance.
RE: Core Balance CT
RE: Core Balance CT
RE: Core Balance CT
What if the CBCT is on a busbar with cables? Does it matter if the CBCT is above the cables or on the cables? Should both the cable screens on these 2 scenarios be looped back to the CT? Attachment here.
RE: Core Balance CT
RE: Core Balance CT