Patent GB-566168-A (GB)
Title: Improvements in electric generators
IPC: H02K23/20
Filed: 1943-04-14
Abstract: 566,168. Dynamo-electric machines. MAcFARLANE ENGINEERING CO., Ltd., MAcFARLANE, J. W., and MAcFARLANE, W. I. April 14, 1943, Nos. 5973 and 19599. [Class 35] A cross-field generator comprises an armature with its conductors pitched at approximately 90 electrical degrees, main and control poles, main-pole commutator brushes connected to the load circuit, control-pole brushes interconnected by a short-circuiting link which may include field coils distributed over the control poles to balance out leakage M.M.F. of armature conductors under these poles, and compensating field coils distributed over the main poles for balancing out armature reaction in the control-pole axis due to the load current. In the construction shown in Fig. 6, the machine has two main poles, each composed of three sub-poles 4, and two control-poles, each consisting of a central section 3b and outer sections 3a, interpoles 5 being arranged between the main and control poles. The brushes x<SP>1</SP>, x<SP>2</SP> are connected to the load terminals 13 in series with windings 13a arranged in the spaces between the sub-poles 4 and the outer subpoles and interpoles, the windings spanning nearly a diameter and providing, together with series interpole windings 13b, compensating M.M.F.s along the control axis, completely balancing the cross reaction due to the load current in the armature conductors 6 under the main poles. Windings 8b around the interpoles and 8a around both the interpoles and the adjacent outer sections of the control poles are connected across the primary brushes y', y<SP>2</SP> and partially neutralize the cross-reaction due to the armature conductors 7 under the control poles and balance out leakage M.M.F. of conductors under the control poles tending to produce across these poles an interfering leakage flux. The characteristics of the machine are controlled by a circuit 9, Fig. 7, having coils 9a wound on the outer sections of each of the control poles and an opposing coil 9b on the central section. The central section is magnetically saturated whilst the outer sections are unsaturated, the air gap 3x under the outer sections being larger than the gap 3y under the central section. In a modified control circuit, two oppositely acting series connected coils are wound on each control pole and a non- linear resistor connected across one coil to divert current therefrom to a proportional extent which increases with rise of voltage across the coil. The part poles may be spaced axially instead of angularly. When the machine is utilised as an exciter for a larger variable speed generator, the control windings 9a, 9b may be supplied from the output terminals of the generator to maintain a constant output voltage. Alternatively, the machine may be used as a self-controlled generator, the control windings being connected across the load terminals so as to make the load voltage largely independent of the speed of the generator. A generator with a drooping characteristic may be obtained by connecting the control windings in series with the load circuit and providing an opposing set of control coils on the control poles and shunted across the load. Specification 308,041, [Class 35], is referred to.