Kitrobaskin,

C.T. stands for current transformer.

In a "normal" transformer we energise the primary with a voltage, and we get perhaps a different voltage generated across the secondary, which depends upon the turns ratio. We can very conveniently use this to step ac voltages up and down.

That is something all of us here will be very familiar with.

A "current" transformer is the exact same type of thing, but it operates in a completely different mode.

We feed a current through the primary winding, and that generates a current in the secondary winding.

It steps current up, or more usually down, depending upon the turns ratio.

That can be very useful for measuring and scaling ac current.

Svetz,

Definitely on the right track.

In order to work as a transformer there needs to be enough inductive reactance for the windings to act as coils, not as a short circuit. We can increase the inductive reactance by adding more turns, or we can do even better by winding our turns around a suitable magnetic material that gives the magnetic flux a much easier path.

All magnetic materials have a figure for permeability which is a direct ratio of the flux increase through the material compared to air, which has a permeability of one.

So magnetic flux = Turns x permeability

As Xl (inductive reactance) increases our coil will draw less current from the ac source.

All this comes at some cost. The magnetic material will concentrate and magnify magnetic flux wonderfully, but only up to the point of magnetic saturation.

Onset of saturation may be gradual, or sudden. Once saturated we loose all our wonderful permeability and we are back to unity.

All this is just for a plain simple ac inductor or coil.

As soon as we add a second winding we have a transformer, but the same rules apply to a transformer as to an inductor.

We need to arrange enough turns, and enough core cross sectional area to carry the magnetic flux without saturation.

We can use a lot of turns and a skinny core, or less turns and a big fat core to achieve the same inductive reactance.

Michael Faraday figured all this out almost 200 years ago, back in the age of sailing ships, swords, and horses.

There is a direct relationship between voltage, turns, core cross section, frequency and flux density discovered by Mr Faraday.

You can juggle all five factors around and end up with a workable transformer.

RMS voltage = 4.4 x number of turns x core cross section in square cm x frequency in Hz x flux density in Gauss.

More commonly known as Faraday's law V= 4.4 N A F B x 10^-8

Note that there is no mention of current in any of this !

How much current your inductor or transformer can carry only depends on heating in the wire.