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PT.27: A LOOK AT VERY FAST TRAINS THE EVOLUTION OF ELECTRIC RAILWAYS The very cutting edge of railway technology lies in futuristic Very Fast Trains running at 350km/h and more. This month we look at the idea's origins, some way-out ideas from around the world and real engineering development in Europe, England and Sweden. By BRYAN MAHER The concept of very fast trains competing on equal footing with passenger jet aircraft is not new. But today the idea has moved from the realms of fantasy into the real world of nuts, bolts, motors and welded steel. We have not yet reached a limit to the speed that wheel driven trains can achieve. By commercial jet, the SydneyMelbourne flying time is 1 hour and 15 minutes for the 700km route, giving an average speed of about 560km/h. True we do not yet have BRITISH RAIL HAS INTRODUCED these VHS (very high speed) trains, pulled by its class 91 locomotives. The locomotives run at speeds up to 240km/h, pulling five tilt-body coaches. 86 SILICON CHIP trains travelling anywhere near that speed but do not think that it is an impossible goal. Since the dawn of railways, researchers and experimenters have toyed with schemes aimed at very high speed rail travel. Many ideas proved impractical but a few very advanced radical inventions are still being pursued. Early linear motors Experiments with high speed rail vehicles have been going on for years. A report from England in the 1950s described how a 4-wheel test truck ran at speeds of 1600km/h on a track a few kilometres long. It had steel rails embedded in concrete TIDS EXPERIMENTAL MAGNETIC levitation train produced by Krauss Maffei in Germany used a linear motor buried in the track for propulsion at quite high speeds. Magnetic levitiation and linear motors are wasteful of energy though and present big problems when it comes to track switching. I and buried in the concrete between the rails were the winding and iron cores of a linear motor. The truck was extremely low, at less than 200mm high, resulting in little air drag. Stopping at the end of the straight track, according to the report, was simple: the truck shot off the track into a large lake! That fascinating little system was not designed with rail travel in mind but was intended to tow heavily laden aircraft up to about 400km/h, to assist take-off. Readers who doubt the ability of a motor to attain such speeds should consider the peripheral speed of a 60Hz, 2-pole synchronous motor which will have an operating speed of 3600 RPM. If the rotor is one metre in diameter, the rotor circumference will run at 678.6km/h. If run at a higher frequency, it would travel even faster. Clearly, a linear motor propulsion system for a train could achieve very high speeds. Wheel-rail problems Do trains actually need steel wheels running on steel rails? This arrangement does give minimum rolling friction but steel wheels cause noise and vibration. Pneumatic tyred trains running on steel tracks have been tried (eg, our monorails and some French suburbans). Experience shows a decrease in noise and vibration at low speeds but such tyres are a failure at high speeds. But does the train need to contact the track at all? Could not the train float above the rails as it speeds along? Yes, in principle this can be done. Fig.2 indicates the idea which is called RUNNING WHEELS LINEAR -MOTION magnetic levitation or maglev. That's nice, but how do you propel it? Three methods have been tried: • Engine driven propellor (as in hovercraft); • Horizontal jet engines; • Electric linear motors. Magnetic levitation Magnetic levitation has been combined with linear electric motors in experimental trains on a limited scale in England and Europe. This system has wheels for emergencies only, the train normalSTRAIGHTENED OUT ROTOR MAKES STRAIGHT LINE MOVING PART GROUND 3-PHASE SUPPLY 3-PHASE STATOR COILS FIG.1: A LINEAR MOTOR IS SIMILAR in principle to the rotor and stator windings of a conventional induction motor laid out flat. The locomotive windings induce currents in the stationary windings under the track and the reaction between the magnetic fields provides propulsion. JANUARY 1990 87 MAG-LEV TRAIN PASSENGER COMPARMENT IR HEIGHT SENSORS FIG.2: THIS IS THE GENERAL ARRANGEMENT of coils for a maglev train. Close control must be maintained over the elevation and transverse alignment of the vehicle. ly floating a few centimetres above a special track, suspended vertically by magnetic fields. As Fig.2 indicates, both elevation and alignment magnets are needed but these can be combined in a V-shaped track arrangement. Control systems to maintain constant height above the track and correct transverse alignment are mandatory. Train sensors continuously measure elevation and side clearances, feeding data to the control electronics. Some designs have used lifting/repulsion magnets, others have tried magnets above and below the rails. Experimental maglev trains were built in Japan, England and Germany and the latter country proved that B00km/hr is possible, at least over a short distance. In Munich, the Krauss Maffei organisation built the Transrapid-04 Maglev test vehicle and track for further research. Also in Germany a twosection maglev train was designed to carry 96 passengers at 400km/h. In these maglevs, magnets provide the lift as well as both traction and braking forces. In the USA, the Department of Transportation sponsored the Grumman company in building a jet propelled vehicle and special 88 SILCON CHIP track. However, this may be classed as a guided hovercraft rather than a train. British Rail Research, always interested in faster and better railways, espoused a maglev train system between Birmingham National Exhibition and the airport. The tolerance achieved in elevation above rail and transverse alignment was ± 13mm. Fantastic! But that installation did point to the probable future role of maglevs; in short, fast, comfortable shuttle services in crowded cities. Magnetic field problems Still, the world's railways have not rushed to install maglevs on useful long distance trains. The advantages of a smooth ride free of the imperfections of wheels, rails and the variable contact forces between them may be attractive but the strong switched magnetic fields produce problems. The magnetic fields are not completely confined to the motor-track space (the ideal aim). Rather, strong leakage fields can pervade the whole carriage. And because the magnetic fields are switched, they could induce currents in anything conductive within the passenger compartments. This means that harmful stray currents could flow in all structural metal and in the electronic control and communication circuits. Harmful currents could pass through the passengers too, particularly if they have heart pacemakers! And in today 's energy conscious world, maglevs appear to have a further disadvantage because they are very wasteful of energy. As well as the power needed for acceleration and traction, maglevs consume large amounts of electricity in the lifting magnets. Future superconducting magnet coils could overcome this problem. Another problem: how do you change tracks when the train is virtually captured between those magnetic guide rails? This is a worse problem than that described in the episode on monorails! Conventional trains With these problems unlikely to be overcome in the foreseeable future, it seems likely that steel wheels on steel rails will be with us for a long time yet. So how do we increase the running speed? Many factors help to slow down locomotives and trains: • Sharp curves on existing rail corridors; • Steep hills; • Underpowered locomotives; • Insufficient ballast around sleepers, causing spongy track; • Rails too light; • Bogie suspension systems inadequate at high speeds; • Too much unsprung weight in bogies; • Bearing resistance in bogies; • High drag coefficient, leading to air turbulence at high speeds; • Air drag and flying effect of pantographs in electric locos; • Inadequate braking at very high speeds where wheel-rail grip is reduced. Sharp curves Sharp curves are the most serious problem for very fast trains. In fact, they are worse than heavy grades. The density of built up areas in England and parts of Europe (particularly Switzerland with so much mountain country) will not allow WHILE SELF-STEERING BOGIES can negotiate track curves at very high speeds, the passengers object to being thrown from side to side. If track curves cannot be straightened, the solution is to automatically tilt the coach bodies while not moving the centre of gravity. This system, devised by ASEA/ABB, keeps wheel loading constant. new straighter tracks to be built. This has prompted years of research into tilt-body passenger carriages. the floor automatically moves to the right. The aim is to keep the car wholly within the loading gauge. Tilt bodies The speed of a train ascending a steep grade depends directly on the power-to-weight ratio of the train and the running speed at the foot of the hill. Steep grades up to 3. 5 % would be no problem to a very fast train (VFT) if the train had sufficient power-to-weight ratio and there were no sharp curves. Therefore, for speeds above 300km/h any VFT track must be a dedicated new route to allow an almost straight run approaching and ascending hills. Tilt-body passenger coaches are designed to negotiate existing curves above the present speed limits which are set to stop passengers from being thrown from side to side. Bogies, especially the selfsteering type, can be designed to ride at surprisingly high speeds around curves, the limiting factor being the comfort of passengers. To be successful , hydraulic tilting of the coach body must be automatically controlled to suit the speed and track curvature. However, the tilted coach must not move outside the track loading gauge, otherwise it may swipe trackside structures. England and Sweden produced prototype tilting trains but the implementation is not easy. ASEA of Sweden (now ABB) has designed an improved method so that when the top of the car tilts left, for example, Steep grades Rail and ballast For fast travel in safety the track must be exceedingly strong. This means very heavy rail, with 68kg/m rail the top choice. The ballast should extend at least 300mm below and as far out as practicable on each side of the track to prevent sideways movement of the sleepers. Though many modern railways opt for reinforced concrete sleep- ONE OF THE SECRETS OF really high speed running is to use locomotive bogies with low unsprung weight. These bogies, used in the British Rail class 91 locos, have the motors and disc brakes suspended from the loco body rather then being supported directly on the axles. JANUARY 1990 89 ANOTHER COACH TILTING SYSTEM is Talgo, devised by the Italians. The coaches run on shared bogies and are suspended from the top and so are free to swing out on curves. This has the advantage that it is a completely passive system. The drawbacks of Talgo are that the coaches can swing outside the "loading gauge" and therefore may sideswipe trackside structures such as stanchions and signal masts. Wheel and track loading on curves is also uneven. ers, some engineers prefer formed steel units, such as those made by BHP. Steel may be superior to concrete in areas subject to heavy frosts followed by sunny days. Under such conditions the wide temperature changes can possibly initiate hairline cracks in concrete, leading to loosening of rail ties. These effects have been reported in parts of the USA. Bogie suspension The bogie suspension should keep the wheels in contact with the rail at all times. That's not a joke it's a real problem at very high speed. More than this, the suspension must minimise any change in weight-per-wheel during acceleration, braking or traversing of curves. Something as close as possible to independent wheel suspension is the aim, while retaining the solid wheel-axle set. For very high speeds, special wheel flange contours are needed to inhibit bogie oscillation when travelling on straight track. The unsprung weight per axle must also 90 SILICON CHIP be a minimum. This is a major problem in motor driven wheels where the classic axle-hung traction motor and axle mounted gear can more than double the weight of a pair of wheels and axle. High unsprung weight results in less than optimum track adhesion and reduced ride quality for passengers. Ideally, unsprung wheelset mass should preferably be below 2 tonnes for high speeds, with a loading of 18 or 19 tonnes per axle. English VHS The new British Rail VHS (Very High Speed) trains were launched on 11 th August, 1989 on the Intercity East Coast main line run from London to Leeds. These VHS trains consist of nine coaches hauled by one 4.7MW (6300hp) Class 91 Bo-Bo electric locomotive. The loco is powered by four 1.2MW DC traction motors, each 6-pole, fully compensated and separately excited. With a wheelset mass of 1. 7 tonnes, the total (unsprung + sprung) weight per axle is light, at just 20 tonnes. Motor mounting To minimise the unsprung weight, the traction motors and brake discs are mounted in the loco body but they hang down within the bogie frame. Traction/braking drive is transmitted via a rightangle gearbox, a sprung quill drive cardan shaft and flexible couplings. This allows the bogie to move relative to the body while the motors continue driving or braking. The 25kV AC overhead supply is fed via a single pantograph to the underslung main transformer. Secondary windings feed the DC traction motors after rectification. Speed, traction power and electric braking are all microprocessor controlled via an asymmetric oil-cooled multiple GTO thyristor bridge. The electric braking is regenerative, with power returned to the 25kV AC overhead catenary and thence to the national grid system. This is the most efficient method of braking and does not uselessly waste energy in resistor heat banks in the locomotive. To enable braking at all times, the traction motor field coils must be excited. To provide this function in the 91 class loco, the field converter uses GTO thyristors with power supplied from batteries . The coaches are a new tilting design. At the rear, a DVT (Driving Van Trailer) is fitted with a driver's compartment. This rear driver's console, with full control of all loco functions and braking, is used when running in the reverse direction. Double ended operation saves considerable turnaround time at terminals. The design principles for this train, as regards vehicle ride quality, track-following and stability, were derived from research previously done on the now aborted British Rail APT (Advanced Passenger Train). 91 Class results The 91 Class locomotives are rated at 240km/h maximum speed with a dynamic electric braking range from 225km/h down to 45km/h. The complete loco weighs 80t and is designed to haul 520t trains on the east coast route by day, or 750t trains on the night run. Most day journeys on the east coast will involve long continuous runs at a steady 225km/h. On the west coast, the more curved route will limit speeds to 200km/h. On both east and west coasts, sleeping car trains will have a top speed of 160km/h. Swedish tilt-coaches Though the first trains using automatic body-tilt ran in Canada, on the UAC Turbo trains, Europe has taken the lead. SJ in Sweden contracted with ASEA in the design and supply of a test high speed train to run on existing tracks but to cut 25% off run time. The design being tested consists of five stainless steel tilt-body cars hauled by an electric locomotive. The last car is also a driving trailer with a driver's console for use on the return trip. The coach body tilts about its own centre of gravity so that no change in wheel-track forces occur. Tilt is limited to ± 6.5° but even so, this allows the ANTRIM TOROIDAL TRANSFORMERS coaches to negotiate curves at speeds 30% faster than non-tilt coaches. Tilt control is initiated by an inertial captured gyroscopic transverse force transducer. This automatically takes account of curve radius, train speed and track superelevation. Should the train stop on a curve the coach automatically returns to vertical position. The tilting coach bogies have self-steering axles to allow operation up to 200km/h on existing tracks with almost negligible flange wear. Next month we will continue this discussion, looking into some high speed trains which are regularly scheduled for speeds above 300km/h. ~ Our thanks to Lars Persson, ABB, SJ, CFF, GEC, Malcolm Parsons, BR, John Nicolson, VFT Australia, Krauss-Maffei and DB of West Germany for data, photos and permission to publish. General Construction OUTER INSULATION OUTER W INDING W INDING QUALITY TOROIDAL POWER TRANSFORMERS, MANUFACTURED IN U.K. NOW AVAILABLE EX-STOCK AT REALISTIC PRICES. INSULATION INN ER W INDI NG - - ; _f-i+ TAX PAID PRICES 15VA 30VA 50VA SOVA 120VA 160VA 225VA 300VA 500VA 625VA 1- 9 10+ 32 .80 31.70 36.00 35.00 37.20 38.50 41.75 40 .35 44.95 43 .50 55.70 52.20 62.00 58.20 72.80 68.25 100.00 93.75 112.00 105.00 Enquiries from resellers and OEMs welcome. Quantity prices and data sheets available on request. Distributed in Australia by Harbuch Electronics Pty Ltd, 90 George St., HORNSBY, NSW, 2077 Phone (02)476-5854 Fax (02)476-3231 JANUARY 1990 91