Busbar protection: a critical review of methods and practice

Partial operating current characteristics to discriminate internal and external faults of differential protection zones during CT saturation

“…1. If there is any fault within the zone, currents from all terminals connected to the protection zone flow towards the zone [11,17], which indicates that all terminal currents during the internal fault are literally in the same phase given that the system is synchronised. In exception, a CT saturation during the internal fault can create a large phase angle difference between the saturated terminal current and other unsaturated terminal currents.…”

“…During an external fault, current flows outbound from the protection zone through the faulted terminal [11,17], which means the direction of the faulted terminal current is opposite to the other terminal currents. Normally, I op = 0 for external fault conditions; however, I op can be high due to CT saturation because when a CT saturates, the fundamental component of the secondary current decreases in magnitude and its angle advances [18].…”