Damper Bars and Their Influence in Operating Homopolar Inductor Alternators for Aerospace Supplies - Part I: Determination of Saturated Time-Dependent Reactances

The commutating impedance of homopolar alternators of medium frequency, as described by Trutt and Erdélyi [1], has to be kept at a low value in order to enable the various arrangements made up from solid-state elements to convert frequencies of 3500 Hz to the usual 400 or 60 Hz used in aerospace supplies. This can be achieved by fitting damping devices into homopolar inductor alternators. To study theoretically the effect of these devices, the inductances of the various windings must be known. This problem is treated here. For this purpose, the two-dimensional model of the alternator and the vector potential analysis of the cross section (as shown by Schenk et al. [2]) is used. Because of the varying position of the stator winding with respect to the rotor teeth, these reactances are time-dependent, and the coefficients of the differential equations describing the commutating (subtransient) regime are time-varying. The calculations were carried out for a 95-kVA, 115/200 V, 5 rotor teeth, 3400-Hz homopolar inductor alternator. The air gap of the alternator was 0.030 inch. Detailed data of the homopolar inductor alternator are in [1] and [6].