The saturation of current transformer can be divided into two categories: one is the saturation caused by the large capacity short-circuit steady-state symmetrical current (steady-state saturation); the other is the saturation caused by the aperiodic component in the short-circuit current and the remanence of the core (transient saturation)
Steady state saturation: when the secondary electromotive force generated by the steady-state symmetrical short-circuit current passing through the current transformer exceeds a certain value, the core of the transformer will begin to saturate. The characteristic of the secondary current in this saturation condition is that the distorted secondary current is pulse shaped. The positive and negative half waves are generally symmetrical. For the protection of reactive current value, such as overcurrent protection and impedance protection, saturation will reduce the sensitivity. For differential protection, the differential current depends on the difference of saturation waiting of mutual inductors on both sides.
Transient saturation: short circuit current generally contains aperiodic component. This will make the current transformer transmission characteristics seriously deteriorated. The reason is that the excitation characteristics of current transformer
In frequency design, the core flux (i.e. excitation current) needs to be greatly increased when the aperiodic component with very low equivalent frequency is transmitted. The secondary current waveform is asymmetric when the transient signal of the transformer is saturated due to the aperiodic component of the port, and the time to start saturation is long. But when the core has remanence, it will increase the saturation degree and shorten the initial saturation time.https://www.ctsensorducer.com/