Patent GB-457193-A (GB)
Title: Current control apparatus for reversing electric motors
IPC: H02P7/00
Filed: 1935-02-18
Abstract: 457,193. Control of A.C. and D.C. motors ; snap-action switches. STRUCKMAN, E., 97, Copse Hill, Wimbledon, London, and NORBALLE, H. J., Harewood, Rickmansworth Road, Watford, Hertfordshire. Feb. 18, 1935, No. 5175. [Classes 38 (iii) and 38 (v)] The circuit of a motor 1, Fig. 1, which is controlled to give continuous and automatic reversals of a driven machine, such as a washing or planing machine, includes a secondary resistance 22, additional to or incorporated with the normal starting resistance 24, the whole, or a sufficient portion, of the secondary resistance being retained in circuit during normal running of the motor, so that undue current surges in the motor circuit are prevented when the motor is reversed under load. The controlling switchgear, which comprises a reversing switch having contacts 2, 12, 13, and a resistance-controlling switch having contacts 3, 14, 15, may be arranged as a single unit or as a double unit connected by a time-lag device. During reversal the starting resistance 24, and additional rotor resistance 22 are in circuit, but during normal running the switch contacts 3 are operated to cut out the starting resistance 24, a part of the resistance 22 also being cut out in the case of large motors. The circuit arrangement in the case of direct-current motors, and where the secondary resistance is incorporated with the starting resistance is described with reference to Fig. 2, not shown. The switchgear, arranged as a double unit connected by a time-lag device, comprises a shaft 4, Fig. 5, carrying the movable contacts 2 of the reversing switch and oscillated by a lever 27 positioned between adjustable stops 28 carried by arms 29, 30, pivoted on the shaft 4 and connected by a spring 31. Catches 32 retain the lever 27 in its operative position and are released by projections 37, 38, on a pivoted lever 34 operated by the controlled machine through screw-and-nut gear, the lever 34 having projections 35, 36, which operate the arms 29, 30. Thus when the lever 34 is operated one of the arms 29, 30, is rotated and the spring 31 strained, so that, when the latch 32 is released the contacts 2 are operated with snap-action. On the shaft 4 is mounted a lever 48, Fig. 6, having projections 46, 47, engaging pivoted arms 43, 44, connected by a spring 45. The arms 43, 44, have stops 41, 42, between which is situated a lever 40 mounted on a shaft 5 carrying the contacts 3 of the resistance controlling switch. Thus the operation of the reversing switch results in operation of the resistance switch, but the latter is delayed by an inertia device consisting of a mass 54 geared to be rotated by a link 52 pivoted to a pivoted arm 51 carrying a roller 50 which is engaged by a roller 49 carried by the lever 40 during the operation of the resistance switch. Thus as the lever 40 is moved under the influence of the spring 45 its movement is retarded until the arm 51 has been raised against the action of the inertia device. The movable switch contacts 57, Fig. 7, are attached to members 59 pivotally carried on pins 60 in a saddle 61 clamped to the operating shaft 5. The fixed contacts are mounted on brackets 67, and springs 63 hold the fixed and moving contacts in engagement.