GB403464A - Improvements relating to the control of direct current electric motors - Google Patents

Abstract

403,464. Rotary transformers. PESTARINI, G. M., 4, Tapton House Road, Sheffield. July 27, 1932, No. 21209. [Class 35.] For preventing surges owing to voltage differences when a metadyne transformer is connected to a supply line, a stator winding is provided arranged to establish a magnetic flux in the rotor such that an electromotive force equal and opposite to the line voltage is developed at the primary brushes. A metadyne transformer is defined as a rotary machine transforming continuous current at constant voltage to a constant continuous current or to a current related to the voltage in accordance with a desired law. The rotor is driven at constant speed by an external motor or other means are provided by which the total power input is automatically adjusted to be equal to sum of the output and the losses at the desired speed. The machine shown is wound for two poles and has four polar salients. The primary brushes 3, 4 are in circuit with the trolley line T and earth G and the secondary brushes 5, 6 with the motors 8, 9. In Fig. 1, the poles 10, 11 carry windings 12, 13 connected to the mains through a switch 14. The field set up by these windings induces a voltage between the brushes 3, 4 when the armature 1 is rotated so that the main switch can be closed. No current flows in the secondary circuits 8, 9. In a modification, Fig. 2, the poles 15, 16 are provided with windings 17, 18 whereby an electromotive force is set up between the brushes 5, 6 and currents flow in the secondary circuits. These set up fluxes in the rotor which induce an electromotive force between the primary brushes 3, 4. The two methods described may be combined, the poles all carrying windings connected in series. After the counter-electromotive force of the transformer has been made equal to the line voltage, a relay may close or permit closure of the switch 7 or such a relay may give an indication that the voltages are equal. In another arrangement, the switch is closed a predetermined time after the energization of the stator windings. An adjustable impedance may be shunted across the switch 7 to limit current rush. In such a case, the machine may be connected to the line when at rest. The windings 12, 13 and 17, 18 may be similarly used and they may be connected in series with an additional adjustable impedance. The motors 8, 9 may be connected in series across the brushes 5, 6.