Patent GB-857454-A (GB)
Title: Improvements in or relating to electric motor controllers
IPC: H02P25/26
Filed: 1957-04-30
Abstract: 857,454. Control of A.C. motors; controllers. IGRANIC ELECTRIC CO. Ltd. April 30, 1957 [May 24, 1956], No. 13771/57. Class 38 (3). To operate a press motor PM at a low speed in the forward direction, contacts 86 of a pressbutton are actuated to energize relay FCR whereby the circuit of a timing relay ITR is opened and that of a forward contactor F is closed. The motor PM attempts to start in the forward direction with all the resistors of networks RN1-RN3 in its secondary circuit, thus providing take-up of backlash in the driven machinery before a high torque is developed. After a short period, relay ITR operates to energize relay T so that contacts 23 are closed to shunt resistors M7, M10, M13 and M16, as well as corresponding resistors in networks RN2, RN3, to provide delayed high starting torque. After a further short period, the relay T is deenergized and the resistors are re-connected in the secondary circuit. The motor continues to run at low speed in the forward direction as long as the contacts 86 remain closed. To operate the press motor at a predetermined speed in the forward direction, a pilot motor 30 is arranged to position a cam-shaft controller 31 at a desired one of sixty speed-points afforded by the latter. When switch 34 is closed, the pilot motor runs in a forward direction until the desired speed-point is reached. The pilot motor rotates shaft 31 whereby cams 32, 33, actuate vernier contacts 1-16 and main contacts A, D, together with similar contacts in the other networks. When the desired speed-point is reached, the switch 34 is opened, and, if the cam-shaft has stopped at the forty-third step, for example, vernier contacts 16 and main contacts A are closed, in addition to corresponding contacts in networks networks RN2, RN3, Fig. 2 (not shown). To start the press motor, contacts 78 are closed and contacts 81 are opened, whereby relays 1CR and SS are energized so that contacts 24 close to shunt resistors M10, M13 and M16. The response of relay FCR energizes the forward contactor F, so allowing the switches 78, 81 to be released. At this time, a coil c is energized to close contacts 52, 53, of a plugging relay PR, the relay being held in this position. The release of relay 1TR is initiated by opening of contacts 107, and relay T is energized for a short period to short-circuit resistor M7 and provide delayed high-starting torque. The closure of contacts 81 establishes a circuit for timing relay 2TR so that relays 1A and 2A are actuated in sequence for accelerating the press motor, until it reaches its predetermined speed by closing contacts 25, 26, in succession. It is possible to latch contacts 81 in the open position to prevent energization of relays 2TR, 1A and 2A. Under these conditions, the motor PM operates at a predetermined low speed determined by the closure of relay SS. The press motor may be accelerated to the speed selected bythe controller 31 by re-closing the contacts 81. Contacts 35 may be manually operated to reverse the pilot motor 30 and to select a lower speed for the press motor by reinserting secondary resistance. Under fault conditions, a trip-switch 80 responds automatically to de-energize relay SS and reinsert resistors M10, M13 and M16. The relays 1A, 2A are also de-energized for further increase of secondary resistance, the trip-speed of the press motor being predetermined by the setting of selector switch 22. To stop the press, contacts 76 are opened to re-insert all the secondary resistance, the contactor F is released, and contactor R is closed for reverse-current braking. Windings a and b of the plugging relay PR are differentially excited, the winding a having constant energization whilst the winding b is connected across the resistance network RN1. When the press motor approaches zero speed, the relay PR changes-over to open the contactor R. The motor PM is operated in the reverse direction by opening contacts 95 and closing contacts 96, 97. Subsequent operation is similar to that for forward operation. Specification 613,024 is referred to.