Modeling of magnetic field diffusion phenomena in a CVT

Abstract

In a current viewing transformer (CVT), current flows through a wire that is surrounded by a toroid-shaped core on which a secondary is wound. The magnetic field associated with this primary current propagates as a wave and can couple into the secondary circuit; however, it moves as a diffusion front through the core material. Modeling of the diffusion of the magnetic field through the core determined that it affects the magnitude and time signature of the voltage induced in the secondary winding when the primary current is produced by a capacitor discharge. During the quarter cycle rise time (227 ns) of the current pulse in the primary, a step response to an incident magnetic field would yield 95.57 percent of the steady state magnetic flux. Since the voltage induced in the CVT secondary is proportional to the time derivative of the magnetic flux, time delay would further distort the CVT current measurement