Patent GB-628831-A (GB)
Title: Improvements in and relating to electric motor equipments and control systems therefor
IPC: H02P3/14
Filed: 1946-09-20
Abstract: 628,831. Master control of D.C. motors. HOLLYER, E. B., and METROPOLITANVICKERS ELECTRICAL CO., Ltd. Sept. 20, 1946, No. 28272. [Class 38(iii)] [Also in Group XXXV] In an electric motor control system of the kind comprising a dynamo-electric machine which has a fly-wheel mass and is adapted during braking of the motor or motors, to receive energy therefrom to accelerate the fly-wheel, the energy so stored being subsequently utilised for driving the motor or motors, the said dynamo-electric machine is a metadyne transformer through which the motor, or motors is or are arranged to be supplied from the line, and control means are provided comprising means to control the metadyne secondary current for motoring and braking of the motor or motors, and means, responsive to the speed of the metadyne exceeding or falling below respective upper and lower limits, to control the metadyne to oppose further rise or fall of speed, said speedresponsive means allowing acceleration or retardation of the metadyne over a range of speed providing the fly-wheel operation. As shown, a metadyne machine MD is adapted to be connected to a supplysource T1-T2 and to supply traction motors M1 and M2, The machine MD is provided with a fly-wheel and is mechanically coupled to a regulator machine RM the shunt winding of which is controlled by a voltage regulator VR in the manner described in Specification 620,850, [Group XXXV]. A motor M is mechanically coupled to a constant-voltage generator G and exciters E, R, and W. The exciter E supplies the traction motor field windings MF1 and MF2 and is provided with a field winding EF1, which is connectable across the armature of the motor M2, and a normally opposing field winding EF2 connectable across the generator G. The exciters R and W, which control the primary and secondary currents of the machine MD respectively, are connected to different diagonals of a bridge formed of the main metadyne field windings MFA-MFD which are arranged on polar projections between the commutation axes of the metadyne. Exciter windings W2 and R2, which are utilized during motoring operation, are supplied, through a polarised rectifier Pl and an axle-driven generator A, from the exciter E. A reversing switch RS3 maintains unidirectional output of the generator A irrespectively of the motion of the train, and is ganged with similar switches RS1, RS2, and RS4. Exciter windings W1 and R1, which are used when the motors act as generators, are connected in a circuit similar to that comprising the windings W2 and R2 but excluding the generator A. A field winding R3 of the exciter R is excited according to the difference of the voltages of the machines RM and G, and a field winding W3 of the exciter W, according to the difference of the voltage of the machine RM and that across a portion of the potentiometer resistor PR, the latter circuit comprising a rectifier P2 or switch G2. The exciters W and R are further provided with field windings W4 and R4 which are respectively connected across shunts in the motor armature and the main metadyne primary circuits. For starting operation, the machine MD is connected across the line, the motors Ml and M2 are connected to the main metadyne, resistors rc1 and rc2 are short-circuited in sequence, and the exciter winding R3. is connected to the generator G so that the fly-wheel machine accelerates to a speed limited by the regulator machine RM. The exciter E is energized to excite the motor field windings MF1 and MF2. The exciter field windings W2 and R2 are also energized from the exciter E, opposed by the axle-driven generator A, which has no effect initially since! it is driven below its critical speed. The windings W2 and R2 establish equal and opposite secondary and primary currents respectively for the machine MD, so that no current is drawn from the line ;and the stored energy of the fly-wheel is used to drive the motors M1 and M2. The exciter E operates as described in Specification 616,916 to maintain the motor field strength constant up to a pre-determinned motor speed, and the field winding W2 is so excited therefrom to adjust the metadyrie secondary current so as to maintain a substantially constant motor armature current. The rectifier P1 operates, however, as described in Specification 628,829, to allow -progressive motor field. weakening without substantial variation of armature current for values of motor speed above a pre-determined level. When the axle-driven generator A reaches its critical speed the excitation of windings W2 and R2 is reduced so limiting the motor speed to a desired maximum. Further movement of a master controller effects short-circuiting of a resistor rl in series with the windings W2 and R2. If the speed of the fly-wheel set drops to a predetermined low limit, the voltage of the machine RM falls and the generator G becomes effective to energize the winding R3 to reduce the primary back-electromotive force of the machine MD and allow the traction motors to be supplied from the line. As described in Specification 628,828, the exciter winding W3 becomes effective, when the voltage of the machine RM has dropped to a given value, to reduce the motor current, and the winding R3 effects a similar increase in the metadyne primary current, so preventing excess line current. Additional movement of the master controller effects an increase of critical speed of the machine A. During coasting the windings R2 and W2 are open-circuited and the fly-wheel machine is retarded to a minimum speed determined by the machine RM. For braking action the windings W1 and R1 are energized to reverse the metadyne secondary current and that machine acts as a motor, receiving current from the motors M1 and M2. The rectifier P2 is short-circuited, by the switch shown or by an additional rectifier, the winding R3 preventing over-speeding of the metadyne and the winding W3 reducing the secondary current so that, if desired, no energy is returned to the line and further retardation of the equipment is maintained by mechanical braking. Further movement of the master controller sequentially short-circuits resistors r11 and r12 in series with the windings W1 and R1. The exciter E may be replaced by two exciters, which are preferably connected in series, supplying the fields of the motors M1 and M2 individually. Further, the two exciters may be replaced by a single metadyne machine according to Specification 628,830. The machines W and R may be replaced by a single machine according to Specification 628,830. A winding on each of the exciters W and R may be supplied to control the line voltage during regeneration or motoring, or both, as described in Specification. 616,917. Specifications 568,156 and 628,827 also.are referred to.