Patent GB-411482-A (GB)
Abstract: 411,482. Master control of D.C. motors. GRAY, W. T., Darroch, Wainwright Road, Altrincham, Cheshire, and ASSOCIATED ELECTRICAL INDUSTRIES, Ltd., Crown House, Aldwych, London. Dec. 5, 1932, No. 34471. [Class 38 (iii).] A regenerative D.C. traction system comprises at least one compound-wound motor A, a main series resistance r, sequentially-operated contactors R1-R4 for cutting out the resistance in stages under the control of a current limit relay L during both motoring and regeneration, switching means for varying the field excitation to obtain further acceleration during motoring and further increase of regenerative current during braking, and a controller C operable by hand or foot for establishing alternately motoring and regenerating connections from a de-energized condition of the motor, the shunt and series fields of the motor being so proportioned that the motor has an inherent characteristic speed current curve which is suitable for the initial stages of both motoring and regeneration, the actuation of the controller C causing the motor to operate first on the said characteristic curve, and thereafter on different characteristic curves suitable for motoring or for regeneration, as determined by the position of the controller. In the arrangement shown, the shunt field SHF of the motor is weakened by shunt resistances rd controlled by contactors E1-E3, to give further acceleration during motoring, and is strengthened by cutting out series resistances rf under the control of contactors E4-E6 to give increased current on regeneration. The motor is started from rest by closing manual switches CB and moving the controller C to the " Motor" position, whereupon the operating coil OCE7 of a contactor E7 is energized to cut out a resistance rrf in the shunt field circuit. Closure of the contactor E7 energizes the operating coils OCT1, OCT2 of contactors T1, T2, and connects the motor to the trolley t with all the resistances r in series. The operating coils OCR1-OCR4 of the contactors R1-R4 are energized in sequence, under the control of the current limit relay L, to short-circuit sections of the resistance r; when all the resistance is cut out, the motor is operating on the inherent characteristic curve. If the controller C is left in the " Motor " position, the operating coil OCM of a contactor M is next energized, to connect a diverting resistance rds in parallel with the series field SF, and to establish an energizing circuit through contacts M-in for the operating coil OCR1 which, with the coils OCR2 and OCR3 was de-energized by the opening of contacts R4-out, when the coil OCR4 was energized. The contactors R1-R3 now operate in sequence to energize the operating coils OCE1-OCE3 of the contactors E1-E3, the operation of which cuts out sections of the resistance rd to accelerate the motor to full speed. By moving the controller C to the " off " position at any time during the acceleration, the control apparatus is de-energized to establish the conditions for coasting. If the controller is then moved to the " Regen. and Brake" position, the contactors R1-R4 are closed sequentially to short-circuit sections of the resistance r. Closure of R4 de-energizes the coils OCR1-OCR3 and energizes a coil OCG for a contactor G which inserts a portion of the resistance rds across the series field SF. The contactors R1-R3 are then again closed in sequence under the control of the relay L to complete the circuits of the coils OCE4- OCE6 which cause the contactors E4-E6 to operate in sequence to cut out sections of the resistance rf. The contactor R3 in closing, establishes the circuit of the operating coil OCB2 of a contactor B2 which subsequently closes and opens the circuits of the coils OCT1, OCT2, so that the contactors T1, T2 open and disconnect the motor from the line, the opening of the contactor T1 at the same time closing the circuit of the coil OCB1 of a contactor B1 and opening the circuits of the coils OCR1-OCR4, so that suitable conditions for rheostatic braking are established. Thereafter the contactors R1-R4 close sequentially to increase the rheostatic braking effect, the contactor R4 also establishing the circuit of a coil OCV whereby the power brake is actuated and the motor finally brought to rest. In the " Regen. and Brake" position of the controller C, the energizing circuits of the coils OCT1, OCT2 are under the control of a relay RR with its operating coil OCRR connected across the motor armature, so that whenever, during regeneration, the voltage across the motor armature is below a predetermined value, the contactors T1, T2 are opened to establish the conditions for rheostatic braking. The adjustment of the current limit relay L may be effected by the means described in Specification 395,068 or mechanically by means of a cam adapted to vary the spring pressure determining the setting of the switch. This relay may also be arranged to effect automatically the operation of the power brake as described in Specification 411,481. Specification 411,541 also is referred to.