Patent GB-329651-A (GB)
Title: Improvements relating to dynamo-electric apparatus for the regulation and control ofelectric currents and machinery
IPC: H02M1/40
Filed: 1929-02-21
Abstract: 329,651. Gill, J. F., and Chaviara, J. N. Feb. 21, 1929. Armatures, short-circuited screens on cores of; rotary converters and transformers; dynamos and motors, cooling.-For controlling electric currents and machinery an apparatus is employed comprising an armature having a primary commutator winding, a secondary winding short-circuited within the armature or connected to a commutator or to slip-rings and an iron mass without field windings surrounding both windings; the armature is driven by a motor the speed of which is made dependent on the speed, the current or the operating potential difference of the motor or other apparatus to be controlled. The primary and secondary windings p, s may be located in closed slots in an iron core i so that the flux path is closed within the core as shown in Fig. 4. In order to prevent saturation of the iron the flux-return path may comprise an outer ring spaced by a small air gap from the armature. The ring may be fixed or rotatable with the armature and need not be laminated. Fig. 6 shows the invention applied for the purpose of maintaining constant the speed of a shunt motor m. The controlling armature a is driven by the main motor m and is provided with two commutator windings p, s. The two sets of commutator brushes are arranged at right-angles to each other, the brushes of the winding p being connected in series with the main motor armature and the brushes of the winding s being connected across the mains. The current in the primary winding p produces a stationary flux which being cut by the secondary winding s produces in that winding an electromotive force which opposes the line voltage, and at the desired speed-exactly balances it. If the load on the motor m increases and the motor slows down, the electromotive force generated in the secondary winding will diminish and current will flow therein from the main. The inclination of the axis of the resultant flux due to the currents in the primary and secondary windings will vary so that an electromotive force is generated in the primary winding which tends to assist the flow of current to maintain constant the speed of the motor. If a squirrel-cage winding is substituted for the winding s, the action will be similar except that energy is wasted in heat instead of being returned to the line. To dissipate this heat, the bars of the squirrel-cage may be extended beyond the armature core and flattened to form fan blades. If a slip-ring winding is used for the secondary winding, the energy may be dissipated in an external resistance. Fig. 7 shows an arrangement in which the current through a series motor is to be maintained constant. The controlling armature a is driven by a shunt pony motor l the armature of which is in series with the motor m and the primary winding p of the controlling armature a. A diverter d is connected across the armature of the pony motor so that the value at which the current is to be stabilized can be varied. In electric welding, a welding arc would take the place of the motor m. Fig. 9 shows a form for maintaining constant potential difference across the terminals of a shunt-wound motor m. The speed of the pony motor l is determined by the voltage across the main motor armature and a potentiometer v is provided so that any fraction of such voltage can be applied to the pony motor armature. Fig. 8 is a wiring diagram for a winch motor, the voltage of which is to be controlled. In the centre position of the controller handle k the main motor armature m and brake-coil n are short-circuited, the current passing through the differential series coil h of the pony motor l is a maximum and the pony motor runs at its maximum speed. Movement of the controller handle k to the right or left establishes main armature connections for running in one direction or the other and also reduces the current through the differential coil h and so reduces the speed of the pony motor. This slowing down of the controlling armature a causes the main current to stabilize at a higher value. In all forms the controlling armature may be stationary and the brushes rotatable.