Wide-speed-range A-C electric system for aircraft

THE USE of variable-frequency a-c generating systems on aircraft has increased greatly in the last few years. One excitation scheme for these generating systems consists of a d-c generator exciter, built integrally with the alternator, which is controlled by a carbon-pile voltage regulator. Special attention must be given to the design of such an exciter to obtain satisfactory performance over a wide speed range. Figure 1 shows a cross-sectional drawing of a 30-kva 3-phase 0.9-power factor 208/120-volt 400/800-cycles-per-second 4,000/8,000-rpm alternator and its exciter. Satisfactory operation is obtained over the entire speed range with load varying from zero to 150 per cent rated value and with various environmental conditions as are encountered on military aircraft. The voltage-regulating controls for this alternator and exciter are similar to those commonly used for constant-frequency a-c power systems.