CT Saturation in Industrial Applications - Analysis and Application Guidelines

Abstract

This paper analyzes the problem of protection class CTs in detail and explains its underlying mechanics. Several actual relays are analyzed in terms of their response to heavily saturated waveforms. A formal, compact and easy to grasp method is shown to present complex relations between the CT response and the response of any given relay. Based on this graphical method one can quickly evaluate the problem and clearly see an alternative solution if a problem truly exists. This exploratory analysis shows that severely saturated CTs only slightly reduce short circuit tripping capabilities of existing relays. Given the typically applied settings, there is no danger of a failure to trip from instantaneous overcurrent functions even in extreme cases of very high short-circuit currents and low-ratio CTs