Patent GB-675691-A (GB)
Title: Improvements in or relating to electronic control system for dynamoelectric machines
IPC: H02P7/34
Filed: 1950-02-27
Abstract: 675,691. Control of several D.C. motors. WESTINGHOUSE ELECTRIC INTERNATIONAL CO. Feb. 27, 1950. [April 19, 1949] No. 4933/50. Class 38 (iii). [Also in Groups XXXV and XL (c)] In e.g. a paper making making machine, a number of rolls 1 ... 6, Fig. 1, are driven at correlated speeds by Ward-Leonard sets, the individual motors M1 ... M6 having their fields energized from a common voltage regulated source, and the generators G1 ... G6 being driven in common by a three-phase motor M, with their fields 15 energized from gridcontrolled rectifier units C1 ... C6 responsive to the difference between a D.C. reference voltage and the rectified output of tachometer alternators A1 ... A6 driven by the respective motors, and excited from the regulated voltage field supply. The speed of the group is manually adjustable from the master reference unit. A current limiting circuit provides an overriding. limiting bias on the control amplifier circuit during stopping and starting. A button controlled "jog" circuit is provided. Starting-jog control-detector-master reference, Fig. 3. The layout for one section is shown with the generator G1 motor M1, tachoalternator A1, as in Fig. 1. The generator field is energized over wires 157, 158 from the control unit C1 (Fig. 4 below). The current limiting part of the control unit is energized over wires 194, 195 by the drop across the generator series (commutation) field 16. Master regulator MR. This regulator comprises potentiometers 32 ... 34 energized from a transformer 28 connected to the A.C. supply L1 L2, potentiometer 33 providing the "jog" reference voltage as described below. Starting. Start button 51 energizes 2CR and timing relay 2TD over 4CR which also applies the reference voltage from potentiometer 32 over contact 43 to transformer 27 in the speed detector to cause the generator field to be energized. As the generator voltage builds up relay VR picks up to energize 5CR to close the main contactor M.C. and maintain the start button circuit over contacts 55, 38. Relay 3CR energized by the main contactor connects the tacho-alternator A1 to the detector. Stopping. Stop button 52 de-energizes relays 2CR, 3CR, 4CR. The timing relay 2TD maintains the main-contactor MC for five or ten seconds until the voltage relay VR drops out. Jog control. Jog-button 50 energizes relay 4CR as in normal starting but not 2CR so that the reference voltage applied to transformer 27 comes from potentiometer 33 over contact 35 instead of the normal reference voltage from potentiometer 34. Speed-detector unit D1. The output from the tachometer alternator A1 and master reference unit MR are connected by transformers 24, 27 to fullwave rectifiers 25, 26 and the difference between the smoothed rectified D.C. voltages appears on lines 78, 79 for connection to the amplifier in the control unit C1. An antihunting connection from a tapping on the generator voltage relay VR is applied through capacitor 84 to a potentiometer in the detector output circuit to provide a component opposing any sudden change in the generator voltage. Control unit C1, Fig. 4. The control unit comprises three parts : (i) a two-stage, A.C. energized D.C. amplifier E1 (see Group XLc), which amplifies the detector unit output from lines 78, 79 to provide a D.C. control bias on lines 141, 142 for (ii) a three-phase, gridcontrolled, gas-discharge rectifier unit F1 energizing the generator field along lines 157, 158 and a current-limiting control H1. Rectifier unit. Three thyratrons 151 ... 153 energized through transformers 154 ... 156 from the three phase supply Ll ... L3 are each supplied with a fixed A.C. bias from individual phase-shift networks 162 ... 166 connected between the anode and cathode, and controlled by a superimposed D.C. bias from the detector amplifier E1. Current limiting. The volt drop across the generator series field appearing on lines 191, 194 is amplified bv A.C. energized twin triodes 171, 172. When the forward current signal output from these valves exceeds the bias voltage across resistor 127 twin triode 173 conducts to develop a backing or limiting bias on the grids of amplifier valves 95, 96. During stopping, i.e. reverse current, whenever the outer leads of the intervalve transformer 99 have sufficiently large positive peaks with respect to the centre-tap diode 170 conducts producing a positive bias tending to maintain the generator field excitation. Constant voltage field supply unit, Fig. 5. The constant voltage for exciting the motor and tacho-alternator fields is obtained from an exciter generator X whose field is excited from grid controlled rectifiers in accordance with the difference between a part of the exciter output voltage across resistance 206 and a constant reference voltage, provided by a neon tube 212 supplied through a rectifier 208 from the A.C. supply. The error voltage is amplified by an amplifier E to control a three-phase rectifier F as shown in the control unit, Fig. 4. Hunting is prevented by a feed back transformer introducing a transient signal in series with the error voltage on sudden changes of field current. Adjustment of signal magnitude is provided by a shunt potentiometer 224, and adjustment of time constant by a series rheostat 226.