current transformer with modification

[Disha Karnataki]

hi everyone
i read a lot about current transfromers and about it's turn ration in most of the cases there is only one primary winding and huge no of turns in the secondary.Ultimately i am now thinking that why there had to be any primary winding. Because the post which i have read says that the single turn present in the primary of the ct """appears like """ it is in series with the core. Then what is necessary for the primary turn ?????? just a core with secondary turn would have been enough!!!!!!!

 

[FvM]

Beyond play of words, how do you think can the primary current couple to the secondary without a primary winding? What's the winding ratio of this "transformer", how do you calculated secondary current?

 

[Disha Karnataki]

yes i got the answer ..
there is no primary winding for some current transformers like in case of toroidial ct.
so if i use this ct to find out the current in a line then the line wire will be passing through the ct(see the dig for ct on google u will get a better picture) without making any internal connections. here line wire itself acts as primary winding & so the turn ratio is secondaryrimary=n:1
so then take effort to calculate secondary current by the know formula ..

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and actually i had to edit my question as the winding ratio for current transformeres... Because it's mentioned oon google that ct sometimes has only one primary winding or no primary winding..so i was confused in this regard,anyway i found the answer

 

[FvM]

Passing the wire through a toroid core (nearly all technical CTs have a toroid core with a straight conductor hrough the center) makes one primary winding not zero.

No idea where you read about current tranformers with "no primary winding", sounds simply erroneous.

 

[Disha Karnataki]

https://www.electronics-tutorials.ws/transformer/current-transformer.html
go to the above link & read the para for toroidial ct's ..

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yes ofcourse i understood that passing the line wire into the ct itself forms the primary winding

 

[PA4TIM]

From your link:
Due to this type of arrangement, the current transformer is often referred too as a "series transformer" as the primary winding, which never has more than a very few turns, is in series with the current carrying conductor.

Conductor is not the same as inductor. The wire goes at least 1 time through the core. That 1 turn forms an inductor and that inductor is in series with the conductor. What part do you not understand ?

And again an other topic about your power theft meter...

 

[Disha Karnataki]

no i got the point it was fvm saying that a transfromer without primary winding is erroneous.
so i provided him that link to see that the website i mentioned earlier has given about the tansfromer with no primary winding..

the paragraph about the toroidial transformer given by the website:
""• Toroidal current transformers – These do not contain a primary winding. Instead, the line that carries the current flowing in the network is threaded through a window or hole in the toroidal transformer.""
after reading this statement everyting was clear about the ct.... for me

 

[FvM]

Yes, it's also clear for me.

I think the tutorial is confusing things by distinguishing between
- Toroidal current transformers
- Bar-type current transformers

altough they are described with an almost identical setup, a straight conductor through the core center. If you read the description thoroughly, you see that "no winding" is also described as a current transformer that "uses the actual cable or bus-bar of the main circuit as the primary winding, which is equivalent to a single turn".

So whatever you describe as a winding or no winding, it uses a single turn.

 

[PA4TIM]

The tutorial formulates it in a way that can be understand the wrong way by some one with not enough knowledge. What they mean to tell is that a torroid curent transformer alone, so not in use, only one winding has. So not like a normal transformer (or inductor) where you have to cut the mains conductor in two and solder both ends of the conductor to the primairy winding ends on the transformer. In this case you just slide it over the conductor.

But as soon as you pass the conductor through the "window" of the torroid, you create a one turn primaire winding and the existing winding becomes the secundairy winding..