Other classes of CTs than P - advantages

[Mat_pe]

What are the advantages of use CTs with class other than "P"? I mean PR, PX, TPS, TPX, TPY, TPZ classes. I know the difference between them but couldn't find any info about pluses of using it. Have any of you had the opportunity to work with CTs with these classes?

 

[RRaghunath]

Class PR is same as Class P.
Class PX etc. are chosen depending on acceptable saturation characteristic of CT. Systems with high X/R require T-class CTs (T stands for transient performance).
PX class are specified for high impedance differential protection.

 

[Mat_pe]

Class PR is same as Class P.
Class PX etc. are chosen depending on acceptable saturation characteristic of CT. Systems with high X/R require T-class CTs (T stands for transient performance).
PX class are specified for high impedance differential protection.

Thank you for your answer.
I have supplemetary question - what will happen when we use "P" class instead of CT with a different class(more recommended). Will it negative affect on work of protection devices hardly?

 

[RRaghunath]

If you could bring a specific case, I will be able to understand your concern.
At the moment, your concern is not clear.
Generally speaking, protection relay manuals include a section detailing CT requirements and it is best to adhere to those requirements while ordering CTs for trouble-free performance of protection.
You will find in the relay manuals that most of the protections can work well with P class as well as with PX class CTs.

 

[Vegemite]

I have been caught specifying P class CTs for differential schemes which have turned out not to be adequate.
Now, I specify PX class wherever it is possible to do so. The problem with P class is that you have no control over the winding resistance which is critical to the onset and severity of CT saturation.