Patent GB-191108853-A (GB)
Title: Improvements in and relating to Means for and Methods of Changing the Frequency of Alternating Electric Currents.
Inventor: TAYLOR ALFRED MILLS
IPC: H03B19/03
Filed: 1911-04-10
Granted: 1912-07-10
Abstract: 8853. Taylor, A. M. April 10. [Cognate Applications, 9493/11, 11,775/11, 20,761/11, and 21,321/11.] Frequency, changing; phase, changing.-If an alternating potential difference of a sinusoidal character be applied to the terminals of the circuit shown in Fig. 1, which comprises a coil a wound upon a saturated core and a coil d upon an unsaturated core, two rushes of current, represented by C, Fig. 2, will occur in each cycle of applied electromotive force E. An electromotive force e will be generated in the coil d on the unsaturated core, the duration and symmetry of which will depend upon the degree of saturation of the core A upon which the coil a is wound. The invention comprises several means of applying this arrangement to the production from a three-phase alternating- current supply of pulsating currents, the frequency of which may be double, or triple, or multiples of the fundamental frequency. Fig. 3 shows three circuits a, z, b, y, and c, x, each of the type shown in Fig. 1, arranged in " delta," (or in " star "), with secondary windings linked with the coils x, y, z and connected in parallel (or in series) to a load L. The three sets of impulses in each circuit in this case combine in the load circuit to produce a singlephase current of three times the fundamental frequency. The combination of impulses may be effected in this and other arrangements by means of a single transformer having a secondary winding in series with the load and linked with all the windings x, y, z. In the arrangement shown in Fig. 7, two parallel single-phase circuits of the type shown in Fig. 1 have their similar windings a, a1 wound around the outer limbs of a three-linked core A, the central limb of which is excited by direct current so that the outer limbs are alternately saturated once in each cycle, thus giving rise to two independent series of impulses such as e, Fig. 2, of the same frequency as the fundamental, but displaced by half a cycle from each other. These two waves combine and give a double-frequency wave in the circuit L; but in order that this double - frequency electromotive force may be better sustained and made more symmetrical, a three-phase current is employed, as shown in Fig. 11, to provide a second pair of impulses displaced by a quarter of the fundamental cycle from the first pair, this latter pair being combined with the first. The terminals D, F supply the transformer system A, Z, Y, and the terminals E, F and D, E are combined inductively in a transformer W to give the quarter-cycle displacement of electromotive force, which is then supplied to a duplicate transformer set B, Z1, Y1. To produce a frequency of nine times the fundamental, a single-phase triplefrequency current obtained in the manner previously described is split into a three-phase current of triple-frequency, and this again is changed into a single-phase current of nine times the fundamental frequency by means of a repetition of the arrangement shown in Fig. 3. Alternatively, the change may be made directly from the fundamental frequency by combining a number of impulses e, Fig. 2, differing suitably in their phase relation and dimensions. In the arrangement shown in Fig. 15, the coils x, y, z correspond to those shown in Fig. 3. A transformer Q having these coils as primaries is wound with four secondaries a, b, c, e, the first being connected to terminals H, J, the second energizing through a choking-coil O, which produces a lag of one third of a cycle, the terminals H, K, and the transformer M supplying the remaining phase J, K, this transformer being excited through reversed connexions by the coil c and also by the coil e through an impedance N imparting a lag of one third of a cycle. Fig. 17 illustrates a method of compounding to prevent drop of pressure at the terminals of the load circuit L with increasing load. The coils a, b, c on the saturated cores are linked with one or more turns in coils P1, P2, P3 in series with the load circuit. These coils on light loads introduce into the circuit L a back electromotive force which falls off as the load increases. According to certain of the Provisional Specifications, the secondary coils of the fundamental arrangement shown in Fig. 1 may be wound upon the saturated core. According to Provisional Specification 8853/11, these may be used in place of the coil on a saturated core, a small transformer with a secondary coil feeding a local circuit for the purpose of making the impulse e, Fig. 2, symmetrical, the phase of this secondary circuit current being adjustable. Referring to the method of doubling frequency, Provisional Specification 9493/11 states that choking-coils may be placed in series with the coils on the outer limbs of the three-limbed core, the secondary windings being also placed upon these limbs. The three-limbed core may be divided into two separate rings, each having a direct current excitation, to diminish hysteresis and leakage losses. According to Provisional Specification 11,775/11, the source of direct-current may be a mercury - vapour rectifier. Specification 20,867/09 is referred to.