Patent GB-479313-A (GB)
Title: Improvements in and relating to electric motor control systems for electric winding gear
IPC: H02P7/34
Filed: 1936-12-05
Abstract: 479,313. Control of D.C. motors. KOLAR MINES POWER STATION, Ltd., and FREEMAN, H. Dec. 5, 1936, Nos. 33429 /36 and 18332 /37. [Class 38 (iii)] Varying E.M.F.; braking.-In a Ward- Leonard system for winding gear, the excitation of the field GF, Fig. 2, of the generator G is shared by an exciter ME driven with the generator and an exciter CE driven at a speed equal or proportional to the speed of the motor M, the exciter CE having a shunt field winding CFS, and a field winding MEF connected to the output of the exciter ME. The field winding MEF of the exciter CE may be connected as shown directly across the output of the exciter ME or, alternatively, in series with that output. a variable resistance MEFR being connected in series in the first case or in parallel in the second case. The shunt field CFS of the exciter CE is in series with a variable resistance CFSR. The controlling resistances are adjusted so that the output of the exciters CE and ME are equal at full speed of the motor M. When the field MEF of the exciter CE is connected across the exciter ME an additional variable resistance CR is connected in its armature circuit. When the generator field controller WLC is moved from a full speed position to a lower speed position, the exciter CE delivers current to the generator field GF at a slightly lower voltage. Deceleration commences and the motor speed falls smoothly and progressively until a speed corresponding to the new controller setting is reached. If the generator field controller is moved to its off position, the exciter ME is disconnected and the generator field is fed from the exciter CE alone and at a lower voltage due to the resistance drop. The motor M is regeneratively braked smoothly and progressively until the exciter voltage falls to a value which causes a relay to introduce mechanical braking. The rate of deceleration is adjusted by the resistance CR, and the variation of energization of the generator in relation to the motor speed is regulated by the resistances CFSR and MEFR. During acceleration with the generator field regulator WLC moved from its off position, the amount of current flowing to the exciter CE from the exciter ME gradually decreases as the motor speeds up until the motor speed corresponds to the setting of the regulator WLC. A circuitbreaker CB limits the amount of current output from the exciter ME and protects the system against an excessive movement of the controller WLC. The resistance CR also regulates the acceleration and may be adjusted from the depth indicator. The acceleration and deceleration control is similar in the case where the field MEF of the exciter CE is in series with the output of the exciter ME. For reversal of the drive the generator field GF and the armature of the exciter CE are reversed as a unit. When the controller WLC, Fig. 3, is moved to one side or the other of its neutral position, the generator field GF and the output of the exciter CE are connected on one side to the appropriate bus-bar BB energized from the exciter ME, and a corresponding switch 1LS1 or 1LS2, is operated through a switch SS1 or SS2, to complete the connections of the field GF and the exciter CE in the appropriate direction. When the controller WLC is returned to its off position, the exciter ME is disconnected but a relay R3 connected across the exciter CE maintains the switch 1 LS1, or 1LS2, operated until the winder speed, and the exciter voltage falls to a predetermined value, whereupon the relay de-energizes the closed switch 1LS1 or 1LS2, and " suicide " connections are completed for the generator field. A solenoid BS, Fig. 4, when de-energized, operates mechanical brakes, and is controlled by a relay BSR having two windings, one VV connected across the output of the exciter CE, and the other R connected through a switch CB2 to the bus-bars BB. The switch CB2 operates with a switch CB1 in the circuit to the controller WLC, and both are controlled by a series of devices, i.e. an overwind switch OSWR, an overload relay OLR, a relay ACFR responding to failure in the supply to an alternating current motor driving the generator G, an overload relay OCR energized in series with the generator field GF, and an emergency switch EPB. Additional devices, i.e. an overspeed relay COSR operated in accordance with the generator speed, a motor field failure relay MFFR and an overwind switch OWS control both coils VV, and R of the relay BSR. When the devices OSWR, OLR, ACFR, OCR and EPB operate the switches CB1, CB2 operate and regenerative braking takes place until the coil VV is insufficiently energized, at a predetermined low speed, to maintain the relay BSR and the mechanical brakes are then applied by de-energization of the solenoid BS. When the devices COSR, MFFR and OWS, operate both coils VV and R of the relay BSR are deenergized and the mechanical brakes are applied. After the switches CB1, CB2 have opened they are reset by a push-button switch.