Patent GB-591055-A (GB)
Title: Improvements relating to control gear for electric motors
IPC: H02P7/293
Filed: 1944-08-29
Abstract: 591,055. Control of D.C. motors. ELECTRIC CONSTRUCTION CO., Ltd., and MILNE, J. C. Aug. 29, 1944, No. 16430. [Class 38 (iii)] Reversing; non-regenerative braking.-A D.C. motor which is reversed by extinguishing the current through one mercury pool type rectifier carrying the motor armature current and building up reversed armature current through another such rectifier, has a dynamic braking circuit connected to the armature under control of a path through mercury pool type rectifiers which is rendered conductive before the motor comes to rest in either direction of rotation ; the braking path may be an additional one through that rectifier which subsequently carries the armature current for reverse rotation. In the Figure a polyphase transformer has a primary winding MP supplied through the push-button controlled main contactor MC and has secondary windings MS1, MS2, ES1, ES2, IS1 and IS2. The motor armature MA is supplied by winding MS1 through rectifier MR1 and series field SeF1 for one direction of rotation and by winding MS2 through rectifier MR2 and series field SeF2 for the other direction. Windings ES1 and ES2 supply the excitation electrodes and may supply the shunt field Sh F which may alternatively be separately supplied. Rectifier control grids ga, gb, gc are supplied by windings IS1 and IS2 through induction regulators to adjust the rectifier output voltage and hence the motor speed. Resistance 24 and adjustable resistance 26 are connected in series between the cathode of rectifier MR1 and the neutral point of induction regulator secondary winding ICS1. Resistances 25 and 27 are connected in series between the cathode of rectifier MR2 and the neutral point of induction regulator secondary winding ICS2. Transformer BT applies across resistances 24 and 25, through rectifiers 9 and 9a, a negative potential sufficient to keep the rectifiers non-conducting until a sufficient opposing P.D. is applied across resistances 26 and 27. These P.D's. are adjustable and derived from potential dividing circuits each made up of condenser 30 or 31, resistance 17 or 17a, and adjustable resistance 32 or 33, supplied from transformer BT through rectifiers 14 and 14a. The rectifiers MR1 and MR2 have extra anodes 34 and 35 connected through braking resistances. BR1 and BR2 to opposite brushes of armature MA, these anodes being controlled by grids 36 and 37 connected to tappings on resistances 24 and 25. The motor may drive the table of a planing machine. The table, as it approaches one end of its stroke with rectifier MR1 in action, closes contacts 28 to short-circuit resistance 26, thereby blocking rectifier BR1, and opens contacts 29. The condenser 31 accordingly charges at a rate determined by resistance 33 until a progressively increasing voltage appears across rectifier MR2 for accelerating the motor in the reverse direction. But since the negative bias on grid 37 is less than that on the other grids, current can flow by way of anode 35 through field winding SeF1 armature MA and resistance BR1 for braking the motor before the other anodes pass current for reversing or for first stopping and then reversing the motor. Contacts 29 and contacts 28 operate in similar manner at the other end of the stroke. The adjustment of resistances 26 and 27 also controls the motor speed and the induction regulators may be omitted. To give a quick return motion to the table resistance 32 or 33 could be disconnected.