Difference between Current Transformer & Ordinary Transf

[shoaibali]

Hi everyone
What is the difference between a current transformer and an ordinary transformer.
I know the difference in their applications.
Is current measurement the only purpose of a CT?
Can an ordinary transformer be used in place of a CT?
Many Thanks

 

[jonw0224]

Construction is slightly different and CT's are calibrated very precisely.

CT's have very few turns (if any) in the primary coil. The primary coil is a large conductor rated for load current (since the CT is in series with the load and the current of the load passes through the primary. There is very little voltage drop across the primary coil.

CT's have a good many turns in the secondary coil. This means that the CT is a step up transformer. So the little voltage drop across the primary becomes significant enough to drive current in the secondary. The secondary of a CT is generally operated with a load (or even a short) across it. The result is a current in the secondary which is proportional and lower than the primary current.

Can you use an ordinary transformer? Technically, yes but you need use the low voltage winding as the primary side and put a load on the secondary side. You also need to make sure the low voltage winding is rated for the load current and has a low impedance. Then you need to take some measurements to calibrate it. If you're thinking about a commercial application, it's probably easier to design and build a CT than to try to use a conventional transformer.

-jonathan

 

[shoaibali]

Re: Difference between Current Transformer & Ordinary Tr

Thanks jonathan.