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How can I sum up the current of two current transformers? Can I simply parallel them or I need an interface between?

You are proposing a combination that is extremely dangerous. If you proceed there is a good chance you will kill someone, probably yourself. :'( Please seek competent on site help.

Fred Townsend

Be careful CTs are dangerous if you don't know what you are doing. Keep them shorted while working with them. If you've never been taught how to work with them, then don't. Since your asking these questions, I assume you need some professional assistance. Please get some.

To answer your questions.
Yes, using instrumentation.
No you cannot parallel them. You need a CT transducer. I use OhioSemitronics at http://www.ohiosemi.com

And then you may need more instrumentation to sum the signals to give you a total.


On August 17, 2004, Anonymous wrote:
> How can I sum up the current of two current transformers? Can I simply parallel them or I need an interface between? <

( Complete thread: http://www.control.com/1026199460/index_html )

You need a donut type current transformer. Them you pass both wire that you want to sum up inside the donut. Both current have to be on the same phase and in sync.

Use a summation CT from Crompton. The Output is 0-5A which is sum of all inputs divided by number of inputs.

CTs are typically paralleled when applying differential protection, re bus differential. The currents don't add in this case.

I'm currently looking at paralleling two sets of CTs (to add the currents) for a directional power relay function. This has been suggested to me by a well-known West Coast utility.

I'm curious if anyone else has tried this.
Pros/cons?

The old Westinghouse books have paralled transformers in the KWH meter sections. However, with new ownership those drawings have been obsoleted. Impedance and misapplication cause people to get hurt.

For safty and balance, a summing ct like Crompton s95p can add simular ratio transformers.

If it is special you can have custom multi-ratio summing transformers made as well.

Alex