Protection Engineering Basics and Schemes Protection Engineering | Page 38
Rated insulation voltage is the maximum level of voltage on which CT insulation will remain secure Impulse voltage is maximum value of voltage which CT can face without damaging in case of lightning Short time thermal current is current of short duration at which ct cannot damage Dynamic current is the maximum value or 2.5times of I th At which CT cannot be damage , but remember the duration of this current must be less then I th
1.1.14 Special Type of CT ( Class X ):
This is unique class of CT defines on the basis of Knee point voltage , rated secondary resistance and nominal secondary current .
We called it customized CT ; the knee point voltages of these sort of points are usually higher then protection class and metering class CT .