Patent GB-624626-A (GB)
Title: Improvements in and relating to electric traction systems
IPC: B61L3/20
Filed: 1946-08-12
Abstract: 624,626. Electric traction. FLETCHER, G. H., and METROPOLITAN-VICKERS ELECTRICAL CO., Ltd. Aug. 12, 1946, No. 23883. [Class 104 (iii)] [Also in Group XXXVII] In an electric traction system for locomotives, trains, trolleybuses, mine haulage, or canal barges, the operation of the traction motors is wholly or in part governed by controlling the supply generator from the vehicle by means of a control current superimposed on the line conductor for the traction current. The conductor line may be sectionalised, with sub-stations, which may be portable, for each section separately controlled. The sub-station for each section may have a generator of limited current type with a falling characteristic, such as a metadyne type. Higher or lower limit characteristics are obtained according to the particular control current imposed on the line conductor by the driver of the vehicle. The sections are normally de-energised, with traction current applied only on entry or near approach of a vehicle and provided that the control current is then superimposed on the sectional line conductor. The generator may have a metadyne exciter or the excitation may be by electronic devices such as thyratrons, or hard valve amplifiers, the anode currents being governed by the control currents. The line conductors may be normally de-energised, except when the controller on the vehicle is in running position. Fig. 1 shows a sub-station with a metadyne generator 1 driven by a polyphase induction motor 2 and provided with a controlling field winding 3 connected to an exciter 4 through a series resistance 5 all or only part of which is included under control of relays 6, 7. The equipment includes alternators 8, 9 producing different frequencies (1,000 and 2,000 cycles per second) the machines 1, 2, 4, 8, 9, being mounted on a common shaft. The alternators are connected by full wave rectifiers 10, 11, operating coils 61, 71 and a capacitance 12 to the conductor F<SP>1</SP> connected to the line conductor of trolley line T, Fig. 2. The locomotive motor has an armature 20, field winding 21 and reverser 22 and is coupled to the collector P by a biased-to-open-position switch 23 with operating coil 24. This coil is connected through a rectifier 34 to a three-way controller 25 having an " off" position 26 and two running positions 27, 28 having capacitances 29, 30 and choke coils 31, 32 which provide two different resonant circuits, circuit 27 being tuned to alternator 8 and circuit 28 to alternator 9. A holding coil 35, in series with switch 23 may be provided to prevent opening of the line switch 23 until the power current is zero and thus prevent arcing. In a modification Fig. 3 (not shown), the exciter 4 is a metadyne and has a controlling field winding tapped and connected to the rectifiers 10, 11, alternator 9 when effective energising the whole of the winding and alternator 8 the tapped part of the winding. In a further modification Fig. 4 (not shown), a single alternator is employed and the controlling winding of the metadyne exciter 4 is connected in series with the alternator and a rectifier, a variable resistance 25<SP>1</SP> (not shown) being provided on the locomotive instead of the controller 26... 28, and a blocking capacitance being inserted between the rectifier 34 and the collector P to prevent flow of power current through the control circuit on the locomotive. To prevent loss of power in moving from one section to another, the collectors should be arranged to bridge the gap in the line conductors T. In order to excite the adjacent sub-station before the gap is bridged, a pilot line conductor may be provided parallel with the'main conductor T and is coupled through a blocking capacitance to the forward conductor F<SP>1</SP>. This method is adapted for both directions of traffic by providing a forward pilot line conductor coupled to the rear feeder. To prevent a second locomotive entering a section from re-starting until the first locomotive has left the section, a relay coil Fig. 6 (not shown) and resistance are placed across line switch 23 and the relay contacts are in series with the rectifier 34. In operation, the coil will be short-circuited when switch 23 is closed and the relay contacts therefore closed, but when the controller has been returned to the off position on entering the section and line switch 23 consequently opened, the energization of the line conductor T due to the presence of another locomotive in the section will energize the relay coil to open the relay contacts and prevent the switch coils from closing the line switch. Several conductor sections T, T1, T2, Fig. 7, may be supplied from a single source by coupling each section through switches 80, 81, 82, which are normally open but are closed by coils 83, 84, 85 connected to rectifiers 86, 87, 88 and control conductor Fl. Thus, each section can only be live when occupide by a locomotive with its controller on a running notch. The traction motor may be controlled by a variable resistor connected across the armature or a series field or both. Where a metadyne motor is used, Fig. 8, switch 23 and reactance 25<SP>1</SP> are connected to the main brushes a, c whilst the auxiliary brushes, b, d, electrically perpendicular to a, c, are connected to an auxiliary field winding 91, which opposes the main field winding 90. The control currents superimposed on the line conductors may govern the anode currents of electronic devices, such as hard valves or thyratrons supplying the exciting current for the metadyne generator. Fig. 9 shows thyratrons, 100, 101 having their anodes connected with a secondary winding 103 of a main transformer whose primary winding 104 is energised from a high-frequency alternator 105. The output circuit of 100, 101 is connected, through a smoothing filter 106, with the controlling winding 3 of the metadyne generator 1. The grids of 100, 101 are connected to the secondary winding 107 of another transformer whose primary winding 108 is connected to a further secondary winding 109 of the main transformer. Phase shifting to vary the mean anode current is provided by capacitances 110, 111, 113, a variable resistance 114 and a choke coil 112. A single controller may be used for reversing all the locomotives coupled in a train by governing the polarity of the line conductors in a section, Fig. 11. Winding 3 is supplied from the output circuit of a phase-sensitive hard valve amplifier 120 having input terminals 121, 122 coupled with the output terminals of a potentiometer 123 and resistor 124 connected with the secondary 125 of a transformer having its primary 126 connected to a high-frequency alternator which is also connected to the amplifier 120. The variable tapping point of 123 is connected with a phase sensitive instrument having operating coils 127, 128, the latter being supplied with'in-phase current from secondary 125 through a ballast resistance 129. On the locomotive, a two-way switch 130, capacitance 131, choke coil 132 and variable resistor 133 are provided. The reversing switch 22 has a polarised operating means 134. The potentiometer 123 is adjusted up or down by the phase-sensitive instrument 127, 128 (governed by the particular position of switch 130 and resistance 133) to vary the polarity of exciting winding of the metadyne generator.