Patent GB-164743-A (GB)
Title: Method and arrangement for increasing the effciency of alternating current power-transmission plants
IPC: H02J3/18
Filed: 1921-06-13
Abstract: 164,743. Kand¾, K. Aug. 16, 1918, [Convention date]. Alternating-current induction machines; rotary transformers; dynamos, regulating; armatures and field magnets.-In induction motor plants subject to greatly varying loads, the voltage of the supply source is regulated proportionally to the square root of the load or to a constant power factor. Fig. 2 shows means for regulating the volts supplied by a transformer T to a motor m by altering the effective secondary turns of the transformer. The arm a, which cuts out turns, is driven by a servomotor S running on a battery b in one direction or the other according to the deflection of an electrodynamometer device K. The dynamometer has two shunt coils n1, n2 co-operating with fixed shunt and series coils n, h respectively, and closes either of two contacts k1,k2 to energize magnet coils r1, r2 and thereby operate the servo-motor through switches g1, g2. With increased load, the watt coils h, n2 prevail and close the contacts k2, g2, thereby causing the arm a to insert more turns until the volt coils n, n1 balance the dynamometer at a predetermined constant ratio of watts/ (applied volts)<2>. In Fig. 3 an arrangement for constant power factor control of a motor m is shown. The motor is fed from a single-phase line d through a phase converter p1, p2 having a rotating magnet p3 and the control is effected by a servomotor S which regulates the field resistance of the exciter U of the magnet p3. The dynamometer K has two coils n1, n2 co-operating with two fixed current coils h1, h. The currents in the coils n1, n2 are in quadrature, for instance by the use of a resistance R and an inductance L. The torques between the pairs of coils h, n2 and h, n1 are respectively proportional to the watt and wattless components of the supply to the motor m, and the dynamometer arm floats so as to maintain a constant predetermined power factor. With high inductance in the coil p1, high insulation need only be used at the line end of its windings. An inductance 1 is placed in the supply circuit, and this, as shown in Fig. 4, may be embodied in the coils p1, which are wound in outer slots separated by restrictions 3 from an inner range of slots containing the three-phase coils p2. Coils 4 are so placed in two of the phases as to link the flux passing through the gaps 3, and inductances x are placed in the third phase. It is shown in the Specification that the coils 4 may be made to compensate the mutual inductance between the windings p1, p2 and that with the motor regulated to a constant value of the ratio, watts/(impressed volts)<2>, the phase converter may be run practically at unity power factor at all loads. Alternatively, the coils p1 may be in an outer row of slots having constricted parts opening radially into the air gap between inner slots containing the coils p2. Fig. 7 shows means for regulating to maximum power factor in the primary side p1 of the phase transformer supplying the motor m under regulation. The dynamometer K has only one movable shunt coil n<3> and a fixed coil h<3> in series with the windings p1. The dynamometer floats when the transformer current and volts are in phase, but with a lag or lead the contacts k1 k2 are closed, as in Fig. 3. to cause the servomotor S and rheostat arm 1 of the exciter U of the phase converter to increase or decrease the excitation with a lagging or leading current respectively. An inductance 10 and shunt 11 ensure the proper phase relation for the coils n3, h3. Adjustable contacts 25, 26 on the, battery b enable the servomotor to run at different speeds in the two directions. To check the tendency of the phase transformer to drop out of step with sudden increase of load, the exciter is provided with a flux shunt 7 between its poles and series coils 6 in addition to the shunt coils 5. An overload relay r3 normally short-circuits the series coils at 8 and part of the flux of the shunt coils is deflected through the path 7. At overloads, the relay r3 is energized at k3 by pressure of the dynamometer arm on a spring- pressed intermediate arm 12, on which the contacts k2 are mounted, and the short-circuit is removed. The flux of the series coils 6 then opposes that of the shunt coils 5 in the path 7 and the exciter volts promptly rise, thereby strengthening the magnet p3. The relays r2, r3 may be ,combined and the relay r3 may also short-circuit the shunt rheostat at 9 to give a further increase in the exciter volts. Further provision for coping with sudden overloads is given by a relay r4 which inserts the starting resistance 24 of the motor m. Extreme movement of the dynamometer arm and arm 12 closes a contact k1 and, in the form shown, causes the relay r4 to open the valve 23 of a liquid rheostat and release compressed air from the lower chamber 22 of the rheostat so that the liquid falls in the upper chamber. For high-voltage circuits the dynamometer coil n3 may be led from low-voltage controlling coils wound in the phase transformer as shown in Fig. 8, in which p<1> is the high-voltage primary winding and j, j<1> the controlling coils. The magnetic axis 15 of these coils is shifted with respect to that 14 of the winding p<1> by an amount which compensates the phase effect of the ohmic resistance of the coils j, j1, this being done by asymmetric winding or by the use of a series auxiliary coil j2 displaced by 90‹ from the coils j, j1. The leakage flux of the windings p1 which escapes the coils j, j1 is corrected by a transformer 16 which injects a compensating voltage in series with the coils j, j<1>. This compensation may also be effected by a coil 17 in the leakage field of the windings p1. Alternatively, the transformer 16 and coils 17 may be eliminated by giving the coils n3, h3 appropriate numbers of turns and arranging their windings substantially parallel to each other so that their mutual inductance compensates the leakage. An inductance 18 is included in the primary side of the phase converter when two or more motors are supplied in cascade, and this is short-circuited when the motors run in parallel. A coil 19 is provided to compensate the phase displacement in the circuit of the coil n3 caused by the additional inductance 18. The Specification as open to inspection under Sect. 91 (3) (a) comprises also the following :-(i) in the case of a number of motors simultaneously fed from a. common source, the application of separate transformers or phase converters to the individual motors or motor groups, the transformer primaries being connected to the common line, and (ii) the use of the controlling coils j, j1, Fig. 8, for supplying current to devices other than the regulating balance V, which are to be controlled by the primary voltage of the phase transformer. This subject-matter does not appear in the Specification as accepted.