German CT Symbol
German CT Symbol
(OP)
Good afternoon,
I am attempting to figure out what is meant by the CT symbol in the attached picture. I work in the US and I have never seen a CT shown like this, especially with two polarity marks.

Thank you!
Kyle
I am attempting to figure out what is meant by the CT symbol in the attached picture. I work in the US and I have never seen a CT shown like this, especially with two polarity marks.

Thank you!
Kyle






RE: German CT Symbol
Not anything "German" about it per se. That's how it would normally be shown in the US too.
Now....why it's done like that, I have no idea.
RE: German CT Symbol
Thanks for the response scottf.
RE: German CT Symbol
Not sure what voltage class these CTs are, but with a ratio of 8000:5A, C800 should be pretty easy to achieve in one unit. Hard to say without seeing the rest of it, but it looks odd to me.
RE: German CT Symbol
Gunnar Englund
www.gke.org
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: German CT Symbol
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Sometimes I only open my mouth to swap feet...
RE: German CT Symbol
I do remember it in school but can not recall the exact meaning.
RE: German CT Symbol
Thank you. I appreciate your responses.
RE: German CT Symbol
I thought the reason why the dots mattered in radar was that Xl for the winding was used for tuned circuits. If you did not follow the dot, you would be 180 degrees out of phase. But in this case your just trying to get a fractional current representing a large current on that phase, but not checking phase. Is this correct?
RE: German CT Symbol
RE: German CT Symbol
It is covered in J.L. Blackburn's Protective Relaying book.
RE: German CT Symbol
RE: German CT Symbol
Thank you.
RE: German CT Symbol
old field guy
RE: German CT Symbol
I don't see how that would work?
You might get a greater burden but if you connect two 800:5 cts in series and run 800 amps through the primary you won't get 10 amps out of it.
I think it's just a connection to mitigate the effects of a spare transformer. If you have a spare on the bushing of a breaker you can't leave it open and if you short is it just gets hot.
RE: German CT Symbol
RE: German CT Symbol
A few points.
As davidbeach correctly points out, protection accuracy is basically a statement of how much voltage the CT can develop on the secondary without saturating. A CT rated C400 can develop up to 400V on the secondary without saturating (not exactly the whole story, but good enough for this discussion).
Look back at the diagram, if each CT develops 400V across its secondary and the CTs are connected in series, then 800V is developed across the pair. Hence the C800 rating as a pair.
"You might get a greater burden but if you connect two 800:5 cts in series and run 800 amps through the primary you won't get 10 amps out of it."
Remember a CT is effectively a constant current source. The burden rating is not related to the current being put out of the secondary at even given time, i.e. a unit rated with twice the burden rating, doesn't put out twice the secondary current....it puts out twice the secondary voltage, or rather can be pushed up to twice the secondary voltage.
"I think it's just a connection to mitigate the effects of a spare transformer. If you have a spare on the bushing of a breaker you can't leave it open and if you short is it just gets hot."
I very much doubt this is the case and if it is, it is a very poor practice. The heat developed in the second CT is essentially the same whether it's shorted or has a burden connected to it. The heat generated in a CT is dominated by the I^2R losses in the secondary. Technically, a CT with a burden across it will generate slightly more heat, as the cores losses will be higher, i.e. operating at a higher flux density.
RE: German CT Symbol
A star for you.