1535221 Parallel operation of alternators LUCAS INDUSTRIES Ltd 16 Feb 1976 [25 Feb 1975] 7754/75 Heading H2H An electrical generating arrangement comprises a continuously-variable-ratio transmission device 13 having input and output shafts 14, 15, a first alternator 16, 17 having a rotor drivingly connected to the output shaft 15, a second alternator 19 having a first winding excitable by a voltage derived from the output of the first alternator 16, 17 and a second winding 26 from which output is derived; an over-running clutch 21 connecting said output shaft 15 and a rotor of the second alternator 19 so that the speed of said output shaft may be less than the speed of said rotor, whereby the frequency of said alternating output provides an indication of speed of said output shaft. As described, three of such systems are combined, the outputs from the three second alternators 19 being connected in parallel via switches 30 to bus bar 28. Each first alternator has a permanent magnet rotor 16 and stator windings 17. Each second alternator 19 includes a first stator winding 22 excited by D.C. derived from the first alternator 18 via a control circuit 31. The rotor 23 is coupled via rectifier 24 to the rotor 25 of the main part of the second alternator 19. Control circuit 31 contains a comparator responsive to the difference in frequency between the three first alternators 16, 17 and is arranged to open the switch 30 associated with one particular channel if the speed (and hence frequency) of that channel is appreciably different from that of the others. The output voltages are controlled by comparing them with a reference and controlling the excitation voltage on lines 29 accordingly.
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