Current Transformer

I am not familiar with any differences.

I am speculating here but I would guess that it is in the way they are used. The CT just outputs a current that is proportional to the primary current. I use CTs for measuring current quite often. We just put a know resistance on the secondary and figure the primary current is (N*Vout/ R), N being the turns ratio. My first guess would be that a protection CT is used to measure current in the same way but the associated circuitry takes some protective action like current limit or shutdown if the measured current is too high (or low). That would imply that it is really a protection circuit that uses a CT as a sensor.

Still that is all speculation.

Anybody else have direct experience with the terms?

shyam gupta; the protection ct is required on electrical services to protect equipment from short circuits on the load side power in the USA on service 1000 amps & larger. perry

Have a close look at the specs and datasheets for each of them (if you have them, and this is not some theoretical or homework question). You will find that the turns-ratio, accuracy, class, etc are all (generally) different. They are designed for different applications (purposes) and designed to interface to different equipment. They are still CTs thou.

If you connect them round the wrong way, your protection and measuring systems will not work properly (or at all).

Accuracy Class & Burden are 2 critical things when considering the use of CT's. A good engineer will make the right decision regarding the situation i.e. will not spend money on 0.5 class high burden CT's when the situation does not require it.

CT's can be connected incorrectly but this is only a problem for the equipment connected to the secondary (incorrect operation). Your biggest concern should be to ensure that shorting links are provided in the secondary circuit of the CT so that maintenance can be done SAFELY.

if measuring CTis wrongly connected for protection purpose, it will not protect the system as it will be saturated on overload.

Although I dont agree to this words, I still vote you as a good answer.

I guess the protect ct will has more thick second wire than front. (Im out of door to electrician)