Patent GB-190702687-A (GB)
Title: Improvements in or relating to the Electrical Transmission of Power.
Filed: 1907-02-02
Granted: 1907-09-26
Abstract: 2687. Siemens Bros. Dynamo Works, [Siemens Schuckertwerke Ges.]. Feb. 2. Distributing.-Power is transmitted electrically from a high speed prime mover, such as a steam turbine, to a low and variable speed machine or apparatus, such as a ship's propeller, by means of an alternating-current generator and a commutator motor or motors having their armatures in direct electric connexion, the generator being excited by a simple circuit independent of the main generator circuit. The speed of the motors is varied by modifying the field excitation of the generator. In the simplest arrangement, Fig. 1, a single-phase alternator g, driven by the turbine t and having its field winding n excited by a battery b in circuit with a rheostat r, supplies current to a series commutator motor m mounted upon the propeller shaft. Similarly, two alternators coupled in parallel may drive two series motors also connected in parallel ; or a single three-phase generator may be employed, a series motor being arranged across each pair of phases. As shown in Fig. 4, the motor m is given a shunt characteristic by impressing upon its field winding d a voltage derived from an exciter e on the turbine shaft, which is in quadrature with the voltage of the main generator g. The latter is excited by a small continuous-current, machine k, and the field windings f, i of the two exciters are fed from a common source b. At starting, the motor field is excited to a maximum while the generator excitation is at a minimum. By increasing the excitation of the generator, the motor runs up to normal speed, higher speeds being obtained by reducing the field excitation of the motor. The control may, for example, be effected by means of a single rheostat p in the field circuits of the exciting-machines, the rheostat arm consisting of a conducting-sector h. The motor is reversed by operating a reversing switch u. In a modification, in which a polyphase generator drives single-phase motors, one for each phase, the armatures are supplied by the main generator, and the field windings by a polyphase exciter having the same number of phases as the main generator but in quadrature with those of the latter. Fig. 6 shows an arrangement in which a polyphase alternator itself supplies the exciting-current for the motors m<1>, m<2>. The alternator has two-phase armature windings p<1>, p<2> connected through adjustable transformers t<1>, t<2> to the motor armatures, the field windings d<1>, d' being connected across opposite phases, as shown. A further development on these lines is shown in Fig. 7. Two two-phase generators g<1>, g<2> are mounted on the turbine shaft, the armature windings p<1>, q<1> and p<2>, q<2> being connected in series with one another and with the armature m<1> or m<2> of one of the motors. Both motors are excited from one generator g<1> only. The field winding n<1> of the generator g<1> is connected directly to the exciter b so as to give a constant potential, while the winding n<2> of the generator g' is fed from the same source through a combined rheostat and reversing-switch h, r. At starting, the switch h, r is adjusted so that the potentials of the two generators are equal and opposite and no current flows through the armatures of the motors ; movement of the lever then serves to cut resistance into the field circuit of the generator g<2> until, in the middle position of the lever, the winding n<2> is cut out. Further movement of the lever l reverses the connexions of the winding n' so that the potentials of both generators are in the same direction. The motor reversing-switches u<1>, u<2> are preferably interlocked with the lever l, so that they can only be operated when the potentials of the generators are equal and opposite.