This paper presents approximate equations that may be used to obtain the lower cutoff frequency fL and higher cutoff frequency fH and thereby the bandwidth of a current transformer. The equations are validated by a PSpice simulation. The Bode plots for both low-frequency range and high-frequency range for a selected design are presented. Also an overview of the various problems that should be considered while designing a current transformer is given, including leakage inductance, stray capacitance, ringing, parasitic resonance, saturation, and mechanical clamping