Patent GB-437669-A (GB)
Title: Improvements in or relating to conversion of alternating currents
IPC: H02M1/22
Filed: 1934-05-04
Abstract: 437,669. Commutator switching arrangements; dynamo-electric machines. PLATEN, B. C. VON, 99, Ostermalmsgatan, Stockhohn. May 4, 1934, No. 13539. Convention date, July 12, 1933. [Classes 35 and 38 (ii)] In an A.C. to D.C. or D.C. to A.C. converting arrangement employing commutators means are provided for superposing a periodic potential on the A.C. supply which causes the resultant potential wave to have parts VI, Fig. 8, of substantially zero potential during which commutation can be effected. The trapezoidal form shown in Fig. 8 is obtained by using an auxiliary potential as shown at L, M, N, O in Fig. 7. In addition distortion of the waveform in this way results in a smoother D.C. potential. In the form shown in Fig. 10 the phase windings L1-L6 of transformers T1, T2 are connected to brushes of commutators K1-K6 the other brushes of which are connected in series and form the D.C. connection 8, 9. The auxiliary potentials are supplied by a generator G1 the windings S1-S6 of which are in series with the phase windings. This machine is preferably a four pole machine and is driven at the same speed as the commutators. In order to get the particular waveform, the poles of the generator Glare of special form and carry windings PI, Q1, Q2 and Q3. The winding P1 is supplied with current proportional to the phase potential from a rotary converter G2 in series with an auxiliary machine G3 which effects a correction due to heating of conductors &c. This auxiliary generator is controlled by a relay R1 connected to brushes 13a, 13. If the zero volt interval is incorrect adjustment takes place. In addition, countercompounding to compensate for drop on load may be used. The winding Q, compensates for reaction of windings S1-S6 and the winding Q2 gives a correction proportional to load current. If the commutation operation is not completed at the right instant correction is effected by the winding Q3 controlled by a relay R2 supplied from brushes 13, 13b. The windings Q3 and generator G3 may be omitted in smaller sized installations. Fig. 11 shows the disposition of windings on a pole. The winding P1 is formed by conductors 44-59, Q1 by 30-43, Q2 by 26-29. The winding Q3 when required is placed in spaces 60, 61. The winding P1 gives flux distribution as in Fig. 12 (not shown). The closed winding Lo on the transformer T1 is to absorb third harmonic voltages due to the non- sinusoidal waveform of voltages. In a modification, Fig. 20 (not shown), to enable a low voltage generator G1 to be employed the winding S1-S6 are connected in circuit through step up transformers. In a further modification of the arrangement shown in Fig. 10 a further main step up transformer is connected between the secondaries of the transformers T1, T2 and the commutators K1-K6. In this arrangement an additional winding in series with the winding P1 is added to compensate for the magnetizing current of the additional transformers, this winding being disposed 90‹ out of phase with the winding P1. The windings Q1, Q2 instead of being supplied direct may be supplied from a generator the field winding of which is energized by the load current. In a further modification shown in Fig. 18 to avoid connection between the high potential D.C. circuit and the commutation generator G7, the load current at the intermediate stage is rectified by means of a commutator and passed through the windings Q71, Q72 of the generator G7. The 12-phase secondary windings of transformers T1, T2 and the 12-phase primary windings of transformers T3, T4 are connected to form a closed ring to which the commutator segments are connected, the load current flowing via the two halves of the ring and the windings Q71, Q72 to ensure satisfactory commutation at the segments an additional auxiliary commutation generator G8 having windings S81a-S86a, S81b-S86e is provided. This auxiliary generator has the usual windings to effect compensation for voltage and load current. In a modification of this the windings S71a-S76a, S71b-S76b are transformer coupled into the main circuits. British Specifications 388,061 and 437,366 and French Specification 754,149, and U.S.A. Specification 661,719 are referred to. Reference has been directed by the Comptroller to Specifications 20867/09, 26390/10, 286,001, [all in Class 38 (ii)], and 389,824.