Field-circuit coupled formulation of transient phenomena in current transformers

A nonlinear, field-circuit coupled finite element model of a current transformer (CT) is presented for simulation of transient conditions. Saturation of core was taken into account by using actual B-H curve of the core material. Some geometrical simplifications were used so that 2-D simulations could be performed with reasonable accuracy. The formulation was realized using commercially available software and implemented for a metering class, 69 kV, 1200/5A current transformer. The normal operation and other cases, such as short-circuit on primary side and high voltage buildup during high burden, are presented. These cases demonstrate modeling flexibility of the field-circuit coupled formulation. The model can be easily extended to analyze other phenomena such as internal faults, inrush current in primary, mechanical behavior under short-circuit condition on the primary side, etc.