CT saturation with differential protection

[mikhe]

A customer of ours is insisting on a greater X/R ratio, i.e. 10 as opposed to 6 as specified, they say this is to accommodate the potential CT saturation.

Could someone explain CT saturation?

CT =
Ratio 1500/1
Class 0.1PL370R11
Max Secondary Resistance @ 75DegC 11ohm

Relay GE Multilin SR 489 gen protection

System is a 690V 1.37 MW genset in island mode.

The reason I question this is on reading the GE multilin installation manual it seems to me that a metering class CT would be sufficient to operate the relay.

Regards

 

[PERRO]

You can read the IEEE Std C37.110-1996: IEEE Guide for the aplycation of current transformer used for protective relaying purposes.

Chapter 4.5 : Dynamic characteristic.

 

[alehman]

It is most important that the CT characteristics match. X/R ratio will determine transient performance. It is important for transient performance of the CT's to match.
See

http://pm.geindustrial.com/FAQ/Documents/489/GET-8402.pdf