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THE EVOLUTION OF ELECTRIC RAILWAYS Of all Australian railways, the Queensland system has in recent years been the most innovative. Its significant achievements include the introduction of a powerful new electric locomotive, a triple bogie unit rated at 2.9MW. Electric locomotive design began in Europe 85 years ago using a single motor and rod-drive copied from steam locomotives. These proved to be immensely strong but incapable of high speeds because of the long fixed chassis mounting the driving wheels. Accordingly the two-bogie type was introduced where each axle is 76 SILICON CHIP driven by its own motor. To obtain sufficient pulling power for freight service, three driven axles (six driving wheels) per bogie were used. Locomotives using two six-wheel bogies have been constructed using six traction motors, with a total power up to 10,000HP (7.46MW). This wheel arrangement is known in Australia, USA and Europe as the Co-Co type. "C" indicates three driven axles per bogie and "o" means that no non-driven wheels exist. In Switzerland the Re6/6 nomenclature would be used instead, where "R" indicates high speed capability, "e" stands for electric and 6/6 shows that there are six driven axles out of a total of six. The Co-Co design has reigned supreme worldwide for all heavy service but it does present problems, particularly on the winding narrow guage (3 feet 6 inches, 1067mm) tracks which make up the Queensland rail system. There are two particular problems: (1). On tight curves the 3-axle bogies incur considerable friction between wheel flanges and the rail inside edge. Wear on both the rails FACING PAGE: CUT-AWAY drawing of a 3000-class triple-bogie locomotive. A lot of equipment is included in the body, including a large transformer ◄ which steps down the 25kV AC overhead supply. (Drawing courtesy Clyde/ASEA- Walkers). and the wheel flanges can be high. (2). The long bogies also cause considerable track deflection which means that maintenance to the permanent way is a constant problem. These two problems could be solved if 2-axle (Bo-Bo) locomotives were used but the greater axle loading could not be tolerated on Queensland's light tracks. The BoBo design also presents a problem in that for a given loco weight, less tractive effort is available before wheel slip is encountered, than for a Co-Co design. Built by Clyde/ASEA-Walkers, this powerful new 2.9MW electric locomotive was the first of a new generation for Queensland Railways. The triple 2-axle bogies allow the loco to negotiate tight curves and give less track deflection than a conventional Co-Co design. Tri-ho locomotives The solution was a really innovative design involving a Bo-BoBo design - that's right, three 2-axle bogies, sometimes called a Tri-Bo configuration. This has one 2-axle bogie at each end of the loco and one in the middle. To allow the loco to negotiate curves, the end bogies swivel as you'd expect while the middle bogie slides from side to side under the loco chassis. This permits the wheels of the centre bogie to self-align with the track for minimum sideways friction. The centre bogie carries one 'third of the total weight, with flexible cables joining the traction motors to the control circuits in the body above. Maximum sideways deflection on the centre bogie, on the tightest curves, is ± 200mm from the centre-line of the loco chassis. With twelve wheels, all driven, six traction motors and short bogie wheelbase, many locomotive designers see this type as ideal. For a given loco weight, it has the same axle loading and tractive effort as a Co-Co design but it has the advantage that each bogie carries only one third of the locomotive weight (rather than half in a Bo-Bo or CoCo design). This point is important in the design of short bridges and culverts. Before electrification, the Queens- RE DTE CONTROL EQUIPMENT ELii'ffllit'rcs CUBICLE Fig.1: this diagram shows how the major equipment is arranged inside the new Queensland Railways 3000 class locomotives. The two end bogies pivot in the normal way while the centre bogies can move sideways by 20cm in either direction to enable the loco to traverse curves. land Railways were transporting over one million tonnes of coal each week from huge open-cut mines in the Blair Athol, German Creek, Curragh and Blackwater districts. From there, the coal was hauled to the ports of Gladestone, Dalrymple Bay and Hay Point, for shipment to the world. Record tonnages were being hauled by the coal trains, pulled by up to six diesel electric locomotives. Each loco was rated at 1.65MW giving a total of 9.9MW (13,270HP) per train. Their huge consumption of diesel fuel was a prime factor in the decision by the Queensland Government to electrify all the state's coal lines. Queensland Railways engineers then faced a number of important questions: (1). What axle loading (weight per axle) and weight per bogie can be withstood by the track, bridges and track bed? (2). What tractive effort and power would be needed in each loco and how many locomotives to use per train? (3). What electrical system to use, what voltage, frequency, AC or DC, and what type of control? (4). Can the one locomotive design perform all the required tasks: express passenger, heavy coal and freight trains? High voltage AC Because of the long distances over 1490km of track was to be OCTOBER 1988 77 ELECTRIC RAILWAYS - CTD electrified - a single phase 25kV AC 50Hz system was adopted. With 25kV AC used on the overhead contact wire, the necessary track substations can be spaced at large intervals. To further reduce the current (and voltage drop) the QR system uses an arrangement of 50kV feeder cables to supply centre-tapped trackside transformers. These produce the 25kV supply for the train overhead contact wire. The 50kV AC feeder supply is derived from the State Electricity Commission's 132kV 3-phase supply fed to substations spaced at about 50km intervals. Locomotive manufacture The State government split the contract for manufacture of the electric locomotives between two Australian companies. The Clyde/ ASEA-Walkers group is building 70 locos, to be known as the 3500 class, at their Maryborough works. Comeng (Commonwealth Engineering) is building the remaining 76 locomotives, to be called the 3100 class, at their Salisbury engineering works. As all locos have the same major specifications, the two classes together are conjointly called the " 3000 class". Both classes make use of microprocessors and high power gate-turn-off thyristors (GTOs) to control the traction motors. Each loco carries a 4.5MV A transformer which steps down the 25kV overhead wire supply to several fixed voltages between 400 and 800 volts with lower voltages for controls and auxiliaries. Each locomotive is equipped with six 495kW (664hp) direct current motors. These are four pole compound wound with compensator windings and interpoles. The whole locomotive is therefore rated at 2.9MW continuous power at the rail. These are geared for a maximum speed of 80km/hour and can produce a continuous 260kN of tractive effort at 40km/hour or a maximum short time rated starting tractive effort of 375kN (84,000lb). The Clyde/ASEA-Walkers group are using ASEA motors while the Comeng company use Hitachi. The motors have series field windings to maximise starting torque and separately excited low voltage shunt field windings to achieve precision control. Bogies Each of the three bogie frames is fabricated from structural steel with critical control and inspection of all welds to ensure long life free of fatigue problems. Primary suspension is by chevrons of rubber which are backed up by helical spring secondary suspension. These afford good isolation of motors and body from track irregularities and vibrations. Traction rods transmit acceleration and braking forces from the bogies to the body. The complete bogie design is vital to the achievement of minimum axle-to-axle weight transfer during acceleration. This allows both motors in each bogie to be driven equally hard without one wheel pair slipping. Thus maximum tractive effort for a given loco weight can be achieved. GTO thyristors As already mentioned, the Queensland 3000 class are controlled by GTO thyristors. Fig.2 shows the essential circuit for the motor controls. Each motor armature is fed by two series phase controlled thyristor bridges connected in series. Each thyistor bridge is fed from a secondary winding on the main transformer. Another secondary winding supplies another thyristor bridge for The Comeng 3100 class is similar to the Clyde/ASEA-Walkers 3500 class but uses Hitachi motors instead of ASEA motors. Comeng is building 76 of these Tri-Bo locomotives at its Salisbury works. 78 SILICON CHIP 25kVAC SDHz DYNAMIC BRAKING RESISTOR REPEAT TRACTION MOTORS 4,5,6 REPEAT MOTORS 2 AND 3 11 OVDC SUPPLY TD MICROPROCESSORS, CONTROL, BRAKES, CRITICAL FUNCTIONS -----1 + 'T' DYNAMIC BRAKING BATTERY CHARGER 110v: SERIES FIELD MOTOR No.1 ..J.. -:; SHUNT AELDS MOTORS 4,5,6 AUXILIARY SUPPLY 3-PHASE 415VAC SOHz ----------''W------TD S NT MoTt:s 2 FlEJ-~s3 , ---------------------------,-\-----SEPARATELY EXCITED SHUNT FIELD MOTOR No.1 WHEEL RAIL Fig.2 partial schematic of the electrical system within the 3000 class locos. SCR chopper circuits are used to control the power to the six traction motors. The locos have dynamic braking but do not employ regeneration to put power back in the grid. the shunt field windings of all traction motors. The phase control signals are derived from microprocessors which take into account the acceleration or braking demands from the driver. The main thyristors are cooled by forced oil flow in , the Clyde/ASEAW alkers locomotives while forced air cooling is used in the ComengHitachi versions. Electrical power for the microprocessors, controlling electronics, running lights and other vital functions comes from the onboard l lODC battery supply. Brakes In formulating the concept of a locomotive for heavy-haul freight, general freight and also passenger service, the designers had little scope for innovation in brake design. Dynamic braking can certainly be provided . on the locomotive, saving wear on brake blocks throughout the train, but for final stopping and emergency use full air brakes are needed. As the new locos will haul both new and old rolling stock, standard air brake systems must be provided. To allow for multiple operation of locomotives by one driver, the braking controls are mounted in a separate rack in the loco and remotely controlled by pneumatic lines from either driver's cab. For dynamic braking, as Fig.2 shows, the armatures of the traction motors are disconnected from the thyristor bridges and connected to heavy duty low resistance braking resistors. The traction motors now act as DC generators, with the degree of braking controlled by the power applied to the shunt field windings. Multiple operation Up to six locos may be used on heavy coal trains with three locos at the front and three near the middle. These coal trains can be up to 2km long! Control for two or three head-end locomotives from any driver's cabin is via a 44-wire cable connecting the adjacent locomotives. Control for the three locos a kilometre away in the middle of the train is by LOCOTROL II, an ingenious radio control system which we will investigate in a later episode of this series. While every locomotive is fitted with a driver's cab at each end, only 39 locos are equipped as command units with LOCOTROL sending equipment. Creep control The maximum tractive effort a locomotive can exert depends on: (1). The total motor power. (2). The gear ratio from armature shaft to axle. (3). The percentage adhesion of the wheel-rail contact; which depends on the wheel and rail surfaces and the weight on each wheel. The QR 3000 class electric locomotives have about the maximum motor power and gear ratio for the weight per axle allowed by the track. Apart from applying sand to the rails, one way to maximise adhesion is to improve the wheelrail surfaces. The polished wheel OCT0BER1988 79 Other auxiliaries include cabin airconditioning, blower fan motors (for traction motor cooling), cooling oil pumps for · the main transformer, thyristor cooling and air compressors for train air brakes. These pumps and blowers are driven by 3-phase 415 volt AC induction motors. The 3-phase 415V AC supply is derived from a single phase to 3-phase converter driven by an extra secondary winding on the main single phase transformer. Comeng have used a rotary machine consisting of a phase motor driving a 3-phase alternator which is hung beneath the loco cab. The Clyde/ASEA-Walkers' locos use a solid-state 3-phase converter instead. Results Clyde/ASEA-Walkers is building 70 of the new 3500 class electric locomotives at its Maryborough works. This photo shows two partially completed bodies. surface resulting from the use of composition brake blocks tends to cause wheel slip. Over the last few years great advances have been made in minimising wheel slip in locomotives and thereby maximising tractive effort. This is called " creep control". It also has the benefit of keeping both driving wheel and rail steel surfaces in the best condition for maximum adhesion. In essence creep control is an automatic control system which makes the loco driving wheels travel up to 5 % faster than the forward speed of the train. This is referred to as "5% creep". Creep also has the effect of continually grinding the loco wheels on the rails so that the wheel contact surfaces remain clean but not polished. Such a surface ensures maximum wheelrail adhesion. Experience has shown that 5% creep is an optimum figure. If more creep is allowed the driving wheels will tend to slip, and produce less tractive effort. Naturally, when less than maximum tractive effort is required, the creep value will be less, as set by the control system. 80 SILICON CHIP To maintain creep at the critical value of 5 % , ASEA has provided radar equipment below the locomotive, to measure true ground speed. Also a tachogenerator measures axle rpm. This then gives a true comparison of wheel periphery speed and rail speed. If the wheel periphery speed is more than 5 % faster than rail speed, the traction motor armature current feedback signal is increased by the creep controller. This feedback retards the phase of the trigger signal for the GTO thyristors supplying armature current, hence reducing motor current and torque to bring the creep back to a figure of 5% . Should the creep be less than 5 % the reverse action increases motor current and speed to regain the optimum creep. Microprocessors do the control functions. Auxiliaries Essential auxiliaries such as the phase control circuits of the GTO thyristor bridges, running lights and emergency lighting are powered by a 110V DC lead-acid battery slung under the loco body. The first loco built, No.3501, rolled out of the Maryborough workshops on Thursday 29 May 1986 and was operating between Rockhampton and Gladstone by 6 September 1986. The first electrically hauled coal train ran in May 1987. The whole electrification program including the main line from Caboolture to Rockhampton and the coal lines in four stages will cost one billion dollars . This money will eventually be repaid by the achievement of faster running times with resultant greater use of wagons, increased revenue and huge savings in diesel oil. These electric locomotives a re eminently successful, with 10,000 tonne trains being hauled by six locomotives at considerably higher speeds than could be achieved by the previous diesel electric locos. Footnote While the 3000 series are the first large order of Tri-Bo locos to be ordered by an Australian railway system and one of the few Tri-Bo classes in the world, the first Australian Tri-Bo loco was the 8650 delivered to the NSW system in October 1985. This was a test bed for the triple-bogie arrangement used in the 3000 class, as built by Comeng. The rest of the 50-strong 8600 class NSW DC electric locos have conventional Co-Co bogies. ~