Motor Differential CTs
Motor Differential CTs
(OP)
I need to spec differential CTs for a 3400kW Induction motor. I wish to use 3CTs instead of 6 (by running the phase and neutral through one CT. The FLC is 204A. The CT supplier is asking for a detailed spec before they make the CTs to order. They need knee point voltage as well as volts per turn. Accuracy class is ClassX - or the equivalant. The fault level is 8kA for 3ph and 3kA for 1ph fault.
Kevin Bosch
Rainbow Technologies





RE: Motor Differential CTs
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If we learn from our mistakes I'm getting a great education!
RE: Motor Differential CTs
Kevin Bosch
Rainbow Technologies
RE: Motor Differential CTs
So much easier to call out the desired C rating and not worry about all those other parameters that go along with the rating; I'd say that even a C200 would generally do quite well in that application (I don't know that relay though).
RE: Motor Differential CTs
If you want the diferential protection, the best is the use of 6 CTs
Fernandoelec
RE: Motor Differential CTs
How can you get the differential current?
RE: Motor Differential CTs
RE: Motor Differential CTs
Muthu
www.edison.co.in
RE: Motor Differential CTs
I hear it called "core balance", and I find it to be VERY common here on the US Gulf Coast. You do need to specify a six-lead motor, so that you have access to both the line and neutral ends of each winding. As David said, both ends of a phase's winding go through a single CT.
You can see an example in the manual for the GE Multilin's SR469 manual under "differential current inputs". There's a picture, too.
Another cool part of the concept is that you don't have to worry about two CT's having different saturation characteristics.
old field guy
RE: Motor Differential CTs
Muthu
www.edison.co.in
RE: Motor Differential CTs
RE: Motor Differential CTs
And yet this is seems to be the best method. Wish I had thought of this idea. :)
Muthu
www.edison.co.in