GB865357A - Improvements in automatic load control systems for parallel connected alternators - Google Patents

Abstract

865,357. Automatic control systems for alternators. SUNDSTRAND CORPORATION. July 19, 1957 [July 25, 1956], No. 22901/57. Class 38 (4). In a system for parallel operation of alternators driven from aircraft engines through constant-speed drive units, the drive units are further controlled in accordance with alternator frequency and loading. Each alternator, e.g. 10, is driven by an aircraft engine through a drive unit 11 which maintains the speed constant as disclosed in Specification 735,194 and is also responsive as disclosed in Specification 813,279 to the output of a magnetic amplifier 25 to adjust the speed both for fine-frequency control and for load sharing. Load sharing.-A current transformer 21 measures the load current in one phase, and with the corresponding transformers of the other alternators is connected in a series loop, Fig. 3 (not shown). There is a contactor 20 linked with each main circuit-breaker to short out the current transformer of an idle alternator. The voltage appearing across the current transformer 21 is the vector difference between the current in that coil and the vector average of the currents in all of the other coils, and this voltage is applied across a resistor 30 in a phase comparator 24 the output of which is the " in phase " component of the current signal. This output is differentiated at 36, 37 and applied to one control winding of the magnetic amplifier 25, and integrated at 38, 39, 40 and applied to a second control winding of the magnetic amplifier 25 to control the driver unit 11. Speed control.-A third control winding on the magnetic amplifier 25 is energized from a bridge circuit consisting of fixed arms 73, 74 and a potential divider 65. The slider of the potential divider 65 is adjusted by the output shaft of a differential gear, Fig. 7 (not shown), the inputs of which are driven by two synchronous motors, Fig. 6 (not shown). One motor is energized from the alternator 10 and the other is energized via a power amplifier from a standard frequency tuning fork. The amplifier 25 adjusts the drive unit 11 to correct the speed. Specification 865,358 also is referred to.