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TWO 86 CLASS LOCOS HEAD up a long train of empty wheat wagons. If the wagons were full, each loco would have both pantographs raised to cope with the huge currents required - over 5000 amps during starting. THE EVOLUTION OF ELECTRIC RAILWAYS Among the most powerful locomotives in use in Australia today are the NSW SRA's 86 class electrics. These are big locos with large driving wheels and they draw enormous currents from the 1500-volt DC catenary. This is the story of the 86 class. By BRYAN MAHER This is an account of a typical freight train operation in New South Wales, starting from Enfield marshalling yards, bound for the western district of the state. Typically, the train will be a mixed assortment of freight cars, all having 2-axle bogies, rated for express speeds. Many of these will be large black louvre vans carrying thousands of cartons and crates from Sydney retailers, small manufacturers and wholesale markets, PT.21: THE NSW 86 CLASS ELECTRICS 82 SILICON CHIP bound for customers living anywhere from Orange to Bourke. There can also be a string of VLine vans brought up on an all-night run from Victoria. The SRA western fast freight was timed to wait for the arrival of the cars on the Melbourne-Sydney-Brisbane overnight express freight, but today the wait had been longer. Finally though, the vans have all been marshalled and the train moves out of Enfield and joins the main western line. For the first part of the journey on the electrified section over the Blue Mountains to Lithgow, the train is pulled by two 86 class electrics. After passing though Parramatta the train begins accelerating for the fast run to Penrith. Each 86 class loco has six 470kW seriesfield 6-pole DC traction motors. These are all switched into the series starting configuration, and wound up to speed as the driver eases up the master controller notch by notch, cutting out series resistance. Each locomotive can exert a starting traction of 420kN (equivalent to 42 tonnes). This is available for the first 10 seconds and as speed builds up, the maximum drawbar pull is reduced to 315kN, the normal acceleration rating permitted for five minutes. As the heavy train gains speed, series starting resistances are progressively switched out by camshaft contactors. In bridging out resistance sections, these camshaft contacts do not break traction currents, so contact burning is minimised and blow-out coils are not needed. TWO 86 CLASS LOCOS pull a long passenger train up a steep grade on the Blue Mountains line. Their maximum rated speed is 130km/h but this is not possible on this section because of the many curves in the line . camshaft contactors to connect large resistors in parallel with the motor field coils. This diverts some motor current away from the coils, to weaken the motor 's magnetic field. When this happens, the armature will build up speed until it again generates a back voltage nearly equal to the applied line voltage. For still higher speed settings of the driver's controller, a number of these field-shunting camshaft contactors will close to divert even more motor current away from the field coils. Maximum field shunting in the 86 class reduces the field current to 37% of the motor armature current, allowing the armature speed to rise as high as 2820 RPM which gives the maximum rated loco speed of 130km/h. The field shunting control camshaft is driven by a pilot motor, controlled by solid state electronics. The ·contacts in the field shunting circuit, because they may break currents up to about 500A, are fitted with magnetic blow-out coils and arc-chutes for arc extinction. To smoothly manage the available acceleration the 86 class locos are fitted with automatically timed controllers for the traction motor circuits, including weakfield runn- Weakfield operation Having reached a speed of around 35 to 40km/h (depending on track gradient, train weight and line voltage] the traction motor armatures, rotating at about 740 RPM, will be generating a back voltage almost equal to the applied line voltage, so the motor armature will rotate no faster as long as the series field coils carry the full motor current. If the driver wishes to accelerate the train to higher speeds the control system then closes additional THE 86 CLASS IS NOT THE most inspiring sight when viewed side on. The ventilator panels are for the compressed air ventilation fans which feed the traction motors and provide cooling for the large starting resistors. ]ULY1989 83 AN 86 CLASS LOCO PULLS into Central Station in Sydney with the Brisl;,ane Limited. On some occasions this train has been diverted over the Harbour Bridge and through the City Circle line. ing, the auto-timed notching process switching the series resistors out of circuit as camshaft operated contactors bridge out resistance sections. The secret of the wonderfully succ'e ssful design of the 86 class is not apparent to the casual observer. How can this locomotive, continuously rated at 2.7MW and with a one-hour rating of 3.328MW exert so much tractive effort? How can the continuous tractive effort of 222kN be extended to double that figure (420kN) for the vital first 10 seconds needed to get a long heavy train moving? Many other classes of locos use a low motor-to-driving wheel gear ratio to achieve high tractive effort, but this prevents them attaining high speeds. Yet the SRA 86 class does achieve both a high running speed of 130km/h and a very high tractive effort. And 'to put the icing on the cake', that enormous tractive effort is achieved (usually) free of wheelslip troubles. Comparisons The SRA 86 class has often been compared to locomotives of other 84 SILICON CHIP railway systems, including the South African 10E and 1 lE classes and the Queensland 3100 and 3500 class 25kV AC locomotives. These use thyristors to control the traction motors, the latter class using a radar system for speed measurement and ultimate control of wheel slip. In the SRA 86 class though, no radar nor thyristors are used, the motor control being solely by mechanical switching as we have seen. This overall scheme has been applied many times over the years in many classes of DC locomotives, so why are the 86 class more successful than many other DC and AC machines? The secret is threefold. • A DC traction motor on a straight DC supply can be given a greater short-time overload characteristic than the same size DC motor in an AC locomotive with rectifiers. • As well as the usual incremental resistance steps in the starting circuit, between each resistance step a second "vernier" resistance bank comes into circuit which in turn contains incremental resistance steps. By this means, the five sections of the main starting resistor are effectively each divided into five vernier resistance increments, equivalent to a starting resistor with 25 individual steps. Furthermore, these 25 effective resistance changes occur in each of the "series", "series-parallel" and "parallel" configurations, making the whole motor control as smooth as a 75 step controller. Thus the voltage applied to each motor is so gradually increased from start to full parallel connection that the tractive effort rises smoothly, resulting in excellent driving wheel adhesion (to the rail). • Wheel slip under ordinary conditions is unlikely but if the driving wheels should slip under severe acceleration or greasy rail conditions, this is automatically corrected. Should any two driving axles differ in rotational speed by as little as 0.4 revs/sec or if any axle accelerates at more than 0.8 revs/ sec2, as sensed by the axle speed generators and associated electronic circuitry, contactors automatically close to shunt the offending motor's armature with a resistance of suitable value. This reduces the torque exerted by that motor until its speed comes back to match that of the others. Rail sanding is resorted to only in extreme conditions. Load capacity Two 86 class locos can pull a train weighing up to 1530 tonnes in the Blue Mountains section. (For downward trains from the western district, they can handle much heavier loads). This would be quite a long train, with somewhere between 30 and 50 wagons, depending on how heavily loaded they are. Such a train is longer than many a passing loop, so the trip from Penrith to Lithgow is run without stop, with the freight chased up the mountains by a lot of passenger traffic. In the afternoon, the Indian Pacific express leaves Sydney, followed by the evening peak traffic - two trains for Mt. Victoria and two for Lithgow, followed by "The Fish" and "The Chips". To ensure the fast freight loses no time with so many trains ALL EXCEPT ONE OF THE 50-strong 86 class are Co-Co machines (meaning 3-axle bogies). The exception is the 8650 shown here which is a Bo-Bo-Bo design with 2-axle bogies. The centre bogie moves sideways to allow the loco to follow curves. Such a design has improved ride and puts less side loading on the rails. "breathing down its neck", a third 86 class would be added at the head end. This is the maximum number of 86 class locos allowed on the one train between Penrith and Lithgow. On the heavy mountain grades the total current drawn by the three locomotives peaks at 8000A on starting, dropping to around 6000A when the train is underway up the long grades. This places an enormous load on the substations and catenary wires. No wonder these locomotives run with all pantographs up to collect such huge currents. No wonder too that both main and auxiliary catenary overhead wires are made of pure copper (different from the steel and aluminium used in other railways). Together with the cadmium copper contact wire, each track has three parallel conductors (ea tenary, auxiliary catenary and contact wire) with a total cross sectional area of 700 square millimetres. On stretches of track elsewhere it is possible to team as many as four 86 class locos together but there are limits on how they can be used. The first limit is dictated by the drawbar strength of the leading wagons while a second limit is the allowable voltage drop and current in the 108V DC control cables running through all four locomotives. Even then, say when hauling the heaviest trains on the Enfield to Kembla section of the Illawarra, only series or perhaps series-parallel notches of the controller are used to minimise current drain. On the Blue Mountains run, no more than three 86 class are used on trains up to 1530 tonnes with the locos starting in the series configuration and running in seriesparallel. The parallel notches are not used, a limitation set by substation and overhead wiring current capacity. Even so, three 86 class locos running in series-parallel and hauling 1530 tonnes of wagons can climb the mountain at speeds up to the limit imposed by the very sharp curves. These include the 241m radius curve near Glenbrook but there are others sharper still at 161m radius. To reduce sideways friction, the 86 class locos are fitted with flange lubricators. From Glenbrook to Katoomba the average grade is 3 % . For this stretch, the motors are run in the full series-parallel configuration. This is necessary to provide enough power on such heavy grades. Voltage drop The very heavy currents drawn by a trio of 86 class locos does cause a considerable variation in the catenary voltage. While it normally sits at about 1500V DC, it can drop to as low as 1150V, as shown on a meter on the driver's console. This does not cause any problems though. The train lights, controls and cab air conditioning will continue to function normally as they are all supplied from a 195kVA 3-phase 50Hz auxiliary alternator JULY 1989 85 THE 86 CLASS HAS A ONE-HOUR rating of 3328kW (4460hp) and a rated drawbar pull of 222kN (22 tonnes). However, it can exert a starting tractive effort of 420kN (42 tonnes). The loco weighs 120 tonnes with a full load of fuel and ballast. driven by a 200kW 1500V DC motor. Automatic solid state voltage and frequency regulators ensure that the auxiliaries are unaffected by line voltage variations. Regenerative braking The catenary voltage can not only drop to around 1150V or even lower but can also go quite high, even when a heavy train is running up the grade. This can be the normal result of a train coming down the grade under heavy regenerative braking. The huge currents so generated by the downhill train are not wasted in resistors as is done in most other rail systems. Instead, the regenerated current is fed back into the overhead line system to drive any train coming uphill. This relieves the trackside substations of a considerable load and saves millions of dollars in energy costs annually. There are very few railroads worldwide using such a money saving scheme. All other systems in Australia and most of those 86 SILICON CHIP overseas allow the train to drive its own motors as generators but simply dissipate all the current generated in high power resistors. This scheme is known as either "dynamic" or "rheostatic regenerative" braking. As long as the current generated by the downhill train is being used somewhere, it will experience a steady braking effect. This means that the air brakes are not needed except in an emergency stop, thus saving on wheel tyres and brake shoes. As a bonus, the brake shoes and wheels are cool when the air brakes are needed. Regenerative safeguards However there is still a problem. What happens if the train going up the mountain has to stop? What happens to all the current being generated by the downhill train? Is regenerative braking still available? The answer lies in the those huge 7.BMW convection cooled resistor banks installed outdoors at each mountain trackside substation. These resistors are automatically switched across the line whenever the uphill traffic is insufficient to provide braking for the downhill traffic. This condition is indicated if the substation DC voltage rises to 1820V DC due to the regenerative action of a downhill train. After allowing for voltage drop in the overhead wiring this corresponds to 2000V DC being generated by the downhill traffic. High current thyristors at each substation perform the necessary switching so quickly that the downhill driver is unaware of any variations in braking effect which would otherwise be caused by uphill trains stopping or slowing down. Electrification ends at Lithgow and from there on all trains are pulled by diesel electrics. By comparison with the 86 class electrics these are weak-kneed machines and nowhere near as energy efficient. Perhaps one day NSW will decide to greatly extend its track electrification and thus gain even greater use from its quiet, powerful, trouble-free 86 class locos. 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