Generator protection and CT saturation problems and solutions

This paper presents a new generator relay design, stator differential function in particular, coping with extreme cases of current transformer (CT) saturation: both AC saturation under large currents and/or residual flux; and DC saturation under low currents but large and long lasting DC components. The algorithm is a subcycle algorithm with fastest times reaching half a cycle including overall response of the relay hardware. Analysis of response of a traditional differential function under CT saturation is included to provide setting guidelines for legacy relays.