Patent GB-600879-A (GB)
Title: Improvements in or relating to variable speed power drives embodying a sectionalisedmotor
IPC: H02P5/68
Filed: 1945-11-14
Abstract: 600,879. Automatic control systems ; rectifying. WESTINGHOUSE ELECTRIC INTERNATIONAL CO. Nov. 14, 1945, No. 30480. Convention date, Nov. 16, 1944. [Classes 38 (ii) and 38 (iv)] [Also in Group XXXVII] A variable-speed power drive embodies a sectionalised motor, comprising a plurality of motor elements all mounted on the same shaft and operating mechanically as a single unit, operated from an alternating-current source, and rectifiers, one for each motor element, are provided for supplying current to said motor elements, said rectifiers and motor elements being connected in alternate series relation. The rectifiers may be supplied in parallel from the alternating-current source and a voltage regulating device connected between said source and the rectifiers. The invention may be applied to the testing of an aeroplane propeller. As shown, three motors 2a, 2b and 2c drive a common shaft, the armatures being supplied through separate rectifier-units 3a, 3b and 3c which are connected alternately in series with the armatures and are connected in parallel to an alternating-current supply 12. A single auto-transformer 11 controls simultaneously the voltage applied to the rectifiers. An exciter 13 supplies the motor field windings 16a, 16b and 16c, control of excitation being effected through a resistor 17 or a control generator 20 which is mounted on the exciter shaft and supplies an exciter field winding 18 through an adjustable impedance 21. A circuit-breaker 72 controls the current-supply to the motor armatures, a starting impedance 22 being connected in shunt therewith. Each rectifier unit comprises a plurality of sequentially-operated mercury arc rectifier valves 101-106, see Fig. 2, of the make-alive type, each comprising a control electrode 27. The rectifiers are supplied from a transformer 23, shown as a double three-phase type, and are excited from a transformer 30 through a common phase-shifter 32 which may be of the induction type. Periodic excitation impulses are applied to the electrodes 27 from a circuit comprising saturable reactors 33, each impulsing system being provided with an individual phase-shifting device comprising a variable reactor 35, the biassing winding 36 of which is supplied from the control generator 20 through a variable resistor 37, which may be of the type described in Specification 527,839. The variable resistor is controlled by a pilot generator 40 which is mounted on the motorshaft and supplies the operating element 41 for varying the resistor 37. The motor speed may be regulated by controlling the pilot generator field winding 45, which is supplied from the generator 20 through a variable resistor 44. The control systems for the phase-shifters 32 and 35 may be interconnected. The alternate series connection has the advantage that the voltage to earth at any point is that due to one motor only, moreover reversal of the arc in any of the rectifier valves results only in a local short-circuit. A reverse current breaker 42 controls a fault in a single rectifier-valve, a polarized relay 43 tripping the breaker of a faulty anode to close a circuit 46 and energize a time-delay device 47 which, after an interval, closes contacts 48 and operates a re-set relay 49 to close any open circuit-breaker 42.