Patent GB-141225-A (GB)
Title: Improvements relating to electric control gear for dynamo electric machines
IPC: H02P1/04
Filed: 1919-05-29
Abstract: 141,225. Barbour, R. H., and Walton, J. R. May 29, 1919. Controllers, actuating-mechanism for.-Relates to motor controllers having an automatic step-bystep action for cutting out resistances, as in starting. The step-by-step movement is produced by reciprocations or oscillations of a member having such inertia in comparison with the mechanical restoring-force that a certain time-limit is ensured between successive strokes. Fig. 1 shows one form of apparatus according to the invention, as used with a set of separate contactor switches each adapted to short-circuit a step of resistance during the starting of a motor. A member a is nearly balanced about a pivot x, so that only a small gravitatory force tends to restore it to the position shown in the drawing. Part of the member is constituted by a soft-iron limb b adapted to be sucked up by a solenoid c. The member also carries a striker s which moves a ratchet-wheel k one step at each oscillation. the ratchet-wheel being attached to a rotatory contact member k<1> having alternate conducting and insulating segments so disposed with reference to a pair of brushes l, m that current is diverted from one brush to the other at each step of the ratchet. A spring roller k<2> is employed to ensure definite positioning. The number of ratchet teeth being equal to the number of separate resistance contactors, all the even-numbered contactors have their actuating-coils connected to the brush l, and the odd-numbered contactors have theirs connected to the brush m. The contactors are of the known kind in which each one controls the actuating-circuit of the next in order, so that the provision of the step-by-step switch k<1> ensures an adequate time-interval between operations of successive contactors throughout the whole series. The apparatus shown further comprises a two-contact relay f, a single-contact relay h having its actuating-coil in series with the motor armature and a pair of switches j, n, of which the former is closed when the member a is in its normal position and the latter in its displaced position. A known form of starting handswitch is used to turn on current to the relay f. When this responds, it makes connexion through e<2> to the solenond c, and thus causes the member a to swing on its axis. The breaking of a contact at p inserts a resistance into the actuating- coil of the relay f, and the opening of the switch j puts a further break in series with the break at p, in order to guard against the possibility of f being fully re-excited before the completion of a stroke. As the member a continues to swing, it closes a switch n for completing circuit to the first contactor, and finally strikes up a plunger d, which, by breaking a connexion at g, opens the holding-on circuit of the relay f. The action then automatically recommences unless the coil of the relay h is receiving too much current, in which case g cannot close to re-excite f until the undue current has decreased to a predetermined maximum. In a modified apparatus, the relay f is not used. Current is turned on from the hand starting-switch direct to the solenoid c, and a mechanical switch is actuated by the member a so that the circuit of the solenoid c, broken at the end of the stroke by the switch g, remains broken until the member has swung right back, irrespectively of any failure of the relay h. The invention may be applied to barrel-type controllers, employing the ratchet-wheel k<1> for direct actuation. Sliding masses working in guides may replace the pivoted member, and springs may replace the gravity control.