Patent GB-962649-A (GB)
Title: Improvements in or relating to frequency changing circuits for alternating current power generating systems
IPC: H02K19/24
Filed: 1960-07-15
Abstract: 962,649. Frequency changing; inductor alternators. CURTISS-WRIGHT CORPORATION. July 15, 1960 [July 7, 1960], No. 24815/60. Headings H2A and H2F. Frequency changing. A frequency converting arrangement for reducing the frequency of current derived from a generator 70 (see below) having field winding 74 and a power winding 76 comprises pairs of back-to-baok S.C.R.'s 100, 102, 104, 106 all connected to one end of the winding 76 (whose other end is earthed) through a capacitor 96, and the pairs being connected to output terminals 124, 126, capacitors 128 connecting these to earth. A vibrator 94 operating at the desired low-frequency supplies current to a transformer 120 provided with windings 116. . . 119 which are connected to the gatecathode circuits of the S.C.R.'s so that these are controlled at the desired low frequency. The vibrator also operates to reverse the supply to the field winding 74 at the low frequency. The capacitor 96 forms a series resonant circuit with the winding 76 to neutralize its inductive reactance. Diodes 930 and lamps 132 are provided to protect the S.C.R.'s against excess control voltage. During one halfcycle of low frequency current the pair of rectifiers 100, 104 will be subject to control, and these will conduct alternately for each halfcycle of the high frequency current charging capacitors 128 so that terminal 124 is positive to 126. During the other half cycle of low frequency current, the rectifiers 102, 106 are subject to the control voltage and conduct alternately so that the charge across the capacitors is reversed. A low frequency output is thereby obtained. To maintain constant output voltage a regulator 134 and a coil 135 are provided. In modifications the generator output may be amplitude modulated before the frequency changing, and a three-phase arrangement may be provided (Fig. 11, not shown). Dynamo-electric machines.-A generator of the inductor type for supplying frequency changing circuit comprises a laminated stator 11 and a concentric laminated rotor 12, the stator having teeth 14-25 and the rotor having teeth 28-41. The stator is provided with field windings 44, 46 which, as shown, are skein type windings each encompassing half the teeth. Toroidal type field windings are also envisaged. A power winding 48 comprising one or more turns wound alternately clockwise and anticlockwise round one or more stator teeth groups is also provided. The rotor teeth are equally spaced, whilst the stator teeth, whose tooth pitch is less than that of the rotor teeth, are grouped in threes in each quadrant to provide N. and S. poles as shown. The difference in pole pitch results in a flux distribution as shown; and the flux cutting the power winding 48 varies a full cycle as the rotor moves on by one tooth pitch. In a modification, Fig. 6, a generator has a stator 71 provided with field and power windings 74, 76, and a rotor 72, stator having major tooth forms 78, each including two minor tooth forms 80, and the rotor having equally spaced teeth 82 of the same pitch as the minor teeth 80. The spaces or slots between the major teeth have a width equal to the sum of the widths of one minor tooth and one minor tooth slot, or multiples thereof, and the power winding 76 and field winding 74 are alternately disposed in these slots. The field winding may be a loop skein winding or a toroidal winding, and the power winding may be a loop skein winding. Polyphase arrangements, and arrangements with more or fewer teeth, are envisaged.