Standard CT accuracy ratings in metal-clad switchgear

Abstract

This paper shows the consequences of low accuracy ratings and analyzes the relay response for fault currents in the range of 25 kA to 50 kA, using the CT accuracy rating from the relay data acquisition. To ensure proper relaying performance, the user should make a careful analysis of CT performance considering the relaying requirements for the specific short circuit current and the secondary circuit impedances. The careful analysis of CT performance for high magnitude offset fault requires computer simulation of the relay, as well as the CT, and cannot be carried out by manual calculation.