-but with a turns ratio of 1:50 , it will be hard to get anywhere near 0.9?
one turn primary isnt going to couple well at all with a 50 turn secondary.
Good coupling is surely important in a current sense transformer, otherwise the outputted current will not accurately be a 50th of the primary current?
I fear, you're making a thing out of it. A single turn is when the current loop goes once through the toroid core, don't matter which way it exactly takes. Everything else is about different amounts of leakage inductance respectively slightly changing K. It effectively won't change the current transmission.Doing a single turn is a bit of a puzzler though.
Beause it could still be a single turn and not actually wrap fully around the core...because the current loop of the single turn goes round the rest of the circuit...so i am thinking of arranging it so that the single turn wraps the spindle of the core as fully as possible....or else i will not get good coupling.?
Notice they don't actually explain what qualifies as "good" coupling or why it's important. Don't just believe some offhand, unsubstantiated comments in an app note. Try the analysis yourself!mtwieg:
we are using one in series with the primary
Third page "choosing a Core" of this article states that its necessary to get good coupling with a current sense transformer....
http://www.mmgca.com/apps/MMG-ctdesign.pdf
Of course there are toroid winding machines. They're actually really cool things.They also say to use a toroidal core, but i imagine that thats very expensive in labour costs to assemble...because someones got to sit there and wrap turns through the core...no machine can do that.
Coupling coefficient shouldn't matter at all for current tranformers. When used correctly, they output current, so the source impedance shouldn't matter. Even a K as low as 0.9 should work fine.
Naturally their is going to be signal loss, as expected from simple models of coupled inductors. This isn't a problem as long as the coupling is known and accounted for (which is way easier than just insisting on having a perfect transformer)..Are you sure?...please see the attached simulation which compares two current sense transformers, one with k=0.9, and the other with k = 1.
The one with k=0.9 suffers more than 10 percent loss of signal.
Surely this is not acceptable?
(its an LTspice simulation)
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