Patent GB-190309015-A (GB)
Title: Improvements in Electrical Generators for Producing Alternating Currents of Low Frequency.
Filed: 1903-04-21
Granted: 1903-06-25
Abstract: 9015. Siemens Bros. & Co., [Siemens & Halske Akt.-Ges.]. April 21. Rotary converters.-A machine for producing single or polyphase alternating currents of low frequency for working electromagnetic percussion drills and similar reciprocating machines consists of a continuous-current dynamo, from one or both poles of which, or from one or more points of the winding of which, a pulsating continuous current is taken, and of a double-pole rotating switch, or two single-pole rotating switches for each alternating-current phase, so constructed and operated that the supply leads for the alternating-current circuit are exchanged exactly at the moment when the pressure of the pulsating continuous current is at zero. By this arrangement, an alternating current is obtained from a bipolar dynamo the frequency of which under the most favourable conditions is only half as great as the number of revolutions. Fig. 2 shows the connections for a bipolar continuous machine and two arrangements of double pole revolving switches for producing a single-phase alternating current. The armature carries, in addition to the collector, a slip-ring which is connected to one of the collector segments, so that at the brush 3 on the ring and at the continuouscurrent brush 1 employed for the pulsating current, the same pressure occurs whenever the brush 1 touches the segment connected with the ring, while after half a revolution of the armature from this position the difference of pressure reaches a maximum, and the pulsating continuous current is thus produced. The switch consists of two halfrings a, b, two slip-rings connected respectively therewith, and four brushes 4, 5, 6, 7, of which two bear on the half-rings and two on the slip-rings, the connections being differently arranged in the two forms shown in Fig. 2. The alternating- current receiver, which may be an induction coil, is represented at s. The gear ratio between the shafts of the armature and the switch in a 2 p. polar machine is always at 2 : p. In a 4-pole machine the switch may, therefore, be on the armature shaft, and only a divided ring and a slipring are required in addition to the collector. A smaller number of revolutions of the switches may be arranged by providing a greater number of ring sections for the exchange of the leads. Sparking at the switch may be avoided, even with any desired phase shift, provided that there is no self-induction in the leads joining the brushes 1-3 to 4-5 and that air gaps are used in the rings, but, when a solid insulating-medium is used it becomes coated, and violent sparking occurs. This is prevented by doubling each of the brushes separating the ring segments by providing a correspondingly large space, and filling in the space with a considerable number of narrow, preferably metallic, pieces insulated like tollector segments, Figs, 5 and 6. Instead of rotating the rings of the switch, the brushes may be rotated, and, in place of a single bipolar rotating switch, two single-pole switches may be used, as shown in Fig. 5. The invention is also adapted for the production of polyphase currents. In Fig. 6, the system is shown applied to the production of two alternating currents differing in phase by 90 degrees from a bipolar machine, both the continuous-current brushes of which are utilized, the pressure of one system being at a maximum when that of the other is at zero. A 4-pole machine may be similarly arranged. The continuous-current leads + and - may supply the generator with energy from a continuous-current network to operate as a motortransformer, or they may serve to take off continuous current from the generator. If provided with the necessary slip-rings, the generator can be worked as a synchronous motor by means of single or polyphase currents, thereby constituting a period transformer which reduces the frequency of an existing single or polyphase current system to onehalf. The generator may be excited by shunt or mixed winding.