Note that unlike ac voltage induced flux, which is sinusoidal in nature, this flux (2) is unidirectional. AC voltage induced flux has zero average value. However, dc offset induced flux does not have this nice feature. The total instantaneous flux in ideal CT core is a summation of ac flux and dc flux (see fig 7.6)
The voltage developed across the CT secondary by the steady state i.e., sinusoidal component of the fault current is given by, . The sinusoidal ac flux in the CT core can be obtained by substituting operator by in equation (2).
Hence, or
Thus, the peak value of ac flux is given by the following relationship.
Hence, the peak value of instantaneous flux in the core is given by,
In practice, if this flux exceeds the knee-point flux in the core (see fig 7.7), then the CT core will saturate.
. The sinusoidal ac flux in the CT core can be obtained by substituting operator 
by 
in equation (2). 
or
