Assessment of losses in the field coil of the compulsator under dynamic conditions

Air core compensated pulsed alternators are being developed as compact power supplies for tactical electromagnetic gun systems. The field coil of the compensated pulsed alternator is a critical component that establishes the excitation magnetic field. Since the machine is air cored, the number of ampere-turns required from the field coil are significant. The rotating nature of the field coil requires that it be light so it can be supported under centrifugal loads. This implies that the current density in the field coil conductors is quite large. Charging the field coil too fast also results in transient losses due to proximity and skin effects. These must be accounted for in the design and simulation of these machines. During the discharge into the load, transient currents flow in the armature winding. These currents produce magnetic fields that interact with the field coils and produce additional losses. This calculation is complicated by the fact that there is relative motion between the conductors. This paper describes a two-dimensional numerical analysis that has been conducted to evaluate the losses in the field coil under these two dynamic conditions.