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THE EVOLUTION OF ELECTRIC RAILWAYS The French railways lead the world in commercially successful very high speed passenger expresses. Their trains, called TGVs, run on dedicated tracks at 300km/h. Now coming on stream is the latest version, the TGV Atlantic. By BRYAN MAHER 94 SILICON CHIP In 1976, the French railways, Societe Nationale des Chemins de Fer Francais (SNCF), achieved world recognition with the building of a dedicated high-speed doubletrack line from Paris to Lyon. After exhaustive tests on locomotives, including a gas turbine type, the French decided on electrification at 25kV AC. By the beginning of this decade, France was busily electrifying 300km of track per year, with a goal of 4000km of new electric track by 1990. The new Paris-Lyon track bypassed all cities enroute, with stops at only two stations close to Le Creusot and Macon. The new tracks run for 388km through rural areas, avoiding any costly civil engineering works. There are no tunnels and no sharp curves. Only TGV (Train a Grande Vitesse) expresses run on these dedicated tracks while other traffic is carried by the old existing route via Dijon. For this reason and because of the high powered electric traction used, track grades of 3.5% are possible. TGVs do not need to skirt around hills - they run straight over the top. The dedicated tracks end at the outskirts of each terminal city. The TGVs then run at lower speed on existing suburban tracks into the city stations. This approach saved millions of francs compared with the cost of high speed tracks through the suburbs. The Atlantic TGV So successful was the Paris-Lyon TGV system following its opening in September 1983 that the philosophy was extended to a number of other cities. The latest system now being built is the Atlantic TGV for TGVA). Construction began on 15th February, 1985. Designed to cover the whole Atlantic seaboard, the new TGV will serve all coastal cities from Brest to Hendaye. By 1990/1991, when full operation is achieved, total passenger rail traffic in this region (population 22 million) is expected to have increased by 33%. WIDLE THE TGV LOCOMOTIVES look quite large, they are very light considering their high power. Rated at 4.4 megawatts (5900 horsepower), they weigh less than 70 tonnes and can travel at speeds in excess of 300km/hr. The Atlantic TGV, though based on the Paris-Lyon experience, has improved passenger accommodation and in-train services. There will be more powerful traction motors and braking systems and a running speed of 300km/h is to be standard throughout. First in service ori the new work was the Brittany section which opened in September 1989. The Aquitane will then come on line at the end of 1990, giving a 3-hour run time from Paris to Bordeaux. In the space of just one decade, SNCF has transformed the railway scene in the eyes of the whole FEBRUARY1990 95 '"Cl n e:; :z: 0 ('") t=: - en cc c,, - - Synrh~ COMPUTER AND SAFETY EQUIPMENT AUTOMATIC COUPLER IMPACT SHIELD BODYFRAME MADE OF HIGH YIELD POINT STEEL 13 - BRAKING CONTROLS 14 - TRACK CIRCUIT CODE SENSORS 15 - EQUIPMENT HOUSING 9 10 11 12 ; ?'.,.,. ::t ~ ZDIIJl!:O: DIRECTION DU MATERIEL 16 - TYPE Y230 POWER TRUCK 17 - TYPE Y237 B TRAILING TRUCK 18-BAGGAGECOMPARTMENT 19 - PASSENGER SEATING 20 - LIGHT ALLOY ROOF PANELS :'C;f TlllS SECTIONED VIEW SHOWS the major components in the TGV locomotives. High power freon cooled GTO thyristor banks provide variable frequency, variable voltage 3-phase drive to the synchronous traction motors. SINGLE ARM PANTOGRAPH MAIN TRANSFORMER CIRCUIT BREAKER. LINE FILTER MICROPROCESSOR-CONTROLLED TRACTION MOTOR FREON COOLING FOR SEMICONDUCTORS 6 - BRAKING RHEOSTAT 7-AU~LIARYPOWERSUPPLY 8 - MAIN COMPRESSOR 1 2 3 4 5 ,: . ··-;_; 2skv/soH C.: ' :. .,. ... , , ::,.,: TGV~ ~~~~ MAJOR COMPONENTS OF THE TGV LOCOMOTIVE commenced. The environmentally conscious approach taken by SNCF actually decreased the overall cost. The whole project was costed at 9.75 billion francs ($US1.625 billion) at June 1986 prices. Tracie For operating speeds of 300km/h, heavy rail, deep track foundations and a new type of concrete sleeper are used. The ballast extends 300mm deep under the sleepers and a strong sub-ballast layer spreads all downward forces over a wide subgrade fill and embankment foundation. In addition, the ballast extends wide and high over the line of sleepers and over 3 metres from the track centre line. This inhibits sideways track movement. L_ TO PREVENT THE TGVs and their passengers from being severely buffeted by standing waves, the tunnels must have a very large cross-section as this diagram of the Vouvray tunnel shows. world. Very high speed rail travel has become a rAalitr. Tunnel problems There are four tunnels required in the first 230km of the Bordeaux route even though, as noted above, tunnels are to be avoided for high speed trains if at all possible. A fast moving train entering a tunnel causes two large displacement sound waves to be created. The head of the train causes a high pressure wave, while the tail of the train causes a low pressure wave. Both pressure waves run ahead of the train at the speed of sound and then reflect from the far (open) end of the tunnel. These effects cause severe standing waves in the tunnel which the train then runs through. Passengers would feel great discomfort from pressure buffeting should this be allowed to occur at the high speeds of the TGV. Tunnels could not be avoided on the Atlantic TGV line. However, the first two tunnels are within 9km of the start of the new line where trains have not yet attained full speed, so they don't cause real problems. But the tunnel at Vouvray, on the high speed section, 210km south west of Paris, needed special atten- tion to minimise air buffeting. The effect can be diminished by either reducing the train speed or increasing the width of the tunnels. SNCF chose larger tunnels. To allow running at 270km/h, the tunnels are cut with a cross sectional area of 71 square metres for double track sections and 46 square metres for single track sections. The parallel single track tunnels at Villejust, 18.7km from Paris, burrow 4.8km through the difficult Fontainbleau fluid sand. To bore through such loose soil, a special full cross-section shield excavator was used. This was quicker than the old fashioned freeze methods once used. Because the shield excavator is more difficult to use on larger tunnel diameters, parallel single track tunnels were drilled rather than one double track bore. Throughout the countryside, the population greatly appreciates the lines being electrified and built around (rather than through) towns. Electric trains give no emissions to pollute the atmosphere or fields, and ugly bridges, flyovers and cuttings are avoided in urban areas. As well, SNCF provided scale models of all major civil engineering works for public discussion well before construction Special sleepers The heavy 60kg/m rails are laid on a new type of sleeper. Each consists of two large reinforced concrete blocks about 300mm deep, 450mm wide and 600mm long, with one rail bolted to each block. They are solidly held at the correct spacing by a steel girder cast into each pair. These more complex sleepers give much more solid location within the ballast, which is important for high speed track. The rails are laid in 396m lengths and then thermit-welded to form continuous track. Signalling A continuous track-to-train signalling system, developed from the Paris-Lyon model, is used on the Atlantic TGV. Lineside signals are not used; instead, the signalling information is displayed on the driver's console. 25lcV system The new Atlantic TGV lines use 25kV electrification, fed at 15km intervals by 50kV/25kV autotransformers. These balance out any unequal currents in both legs of the 50kV power feeder line. This results in a 25% reduction in harmonic interference compared with a straight 25kV transmission line. This system of electrification is FEBRUARY1990 97 AL THOUGH IT IS COMMON TO REFER to the TGV as though it was just one train, the French had over 100 TGV train sets in 1986. identical to that used by Queensland Railways, as described in part 12 of this series. Reduction of train generated harmonics is vital to the railway's own signalling and communication circuits as well as nearby radio, computer and telephone systems. the pantograph because the contact wire is pulled alternately one way and then the other. This spreads the pantograph wear evenly over its contact surface. TGV rolling stock Each TGVA train is 238 metres High speed pantographs SNCF experience shows that with well designed and constructed catenaries and contact wires, set at optimum tension, wear of the contact wire is not a serious problem, even with trains running at 300km/h. The overhead contact wire is of pure copper, with a cross section of 150 square mm. This is tensioned at 20kN (ie, at 2 tonnes) by a hanging weight/pulley system at the anchor posts which are at intervals of 63 metres. This is a phenomenal amount of tension for such a small wire section and keeps the wiring free of excess sag or stretch over the temperature range from + 60°C to -20°C. The catenary wire is of solid bronze, 62 square mm in cross section, and is tensioned at 14kN (ie, at 1.4 tonnes). The pulley tensioning system also has the benefit of reducing wear in 98 SILICON CHIP TGV LOCOMOTIVES HAVE TWO PANTOGRAPHS. This photo shows the larger low voltage (1500V DC) pantograph raised while the high voltage (25kV AC) pantograph is lowered. long with 10 articulated coaches and a locomotive at each end. The coaches ride on large highly flexible airbag secondary suspensions, with sprung free-arm primary suspension. Cylindrical shock absorbers damp out any sway, pitch or yaw, resulting in excellent passenger ride. The electric locomotives are 22.16 metres long, 4 metres high, 2.77 metres wide and weigh only 67.8 tonnes. They are of the Bo-Bo configuration and are propelled by four synchronous motors with variable frequency 3-phase drive. Each motor has 6 poles and is rated at 1.1MW (1475hp) continuous or 1.54MW on an intermittent basis. The two stage gearing to the drive axles gives a train speed of 300km/h at a motor speed of 4000rpm. This requires a motor drive frequency of 200Hz. Being synchronous, the motors rotate at a speed exactly proportional to the motor drive frequency, unlike induction motors which have inherent slip (see Pt.22: 3-phase electric locos). Inverters provide the 3-phase power supply at variable frequency, to produce the desired motor (and train) speed. To enable them to operate at a drive frequency of up to 200Hz or more, the motors are entirely constructed of sheet steel and the magnetic circuit is formed of individually insulated silicon steel laminations. Synchronous motors have a 3-phase AC supply to their stator windings, which sets up a rotating magnetic field in the air gap. The rotor windings (called field coils) are supplied with DC via graphite brushes running on insulated stainless steel sliprings. The brushes are expected to last for more than one million kilometres. The complete motor is only 740mm in diameter, 1110mm long and weighs just 1.45 tonnes. This is incredibly small and light for such a powerful motor. Compared with the 535kW DC motor used on the older TGVs, the new motor gives more than twice the power but weighs slightly less. To further minimise the unsprung weight on each axle, the traction motors are actually supported bv the locomotive body. The motors MOST OF THE BRAKING EFFORT on the high speed TGV trains is regenerative, although the locos and all coaches have large disc brakes. The regenerated power is dissipated in large resistor banks on the roof of the locomotive. hang low, well inside the bogie frame. A 2-stage gearbox in a tripod torque transmission arrangement transfers the drive to the driven train axle. This method, called flange-mounting, allows vertical and torsional movement of the bogie about the fixed motor. Power control On the high speed track sections, the rear locomotive's lightweight pantograph collects the 25kV AC at up to 430 amps from the overhead contact wire. This current is fed to the main transformer primary and then stepped down in four secondary windings for traction plus a fifth winding for auxiliaries. Each traction secondary feeds a harmonic filter and a 4-thyristor bridge rectifier. The 1500V DC from the bridge rectifiers then feeds two 8-thyristor DC to 3-phase inverters in series. The output of each inverter is variable from Oto 250Hz and up to 1246V and 588 amps in each phase to supply one traction motor. The inverters must be forcecommutated when the motors are operating at low rpm to avoid loss of torque. For this reason, the rotor position is detected by magnetic sensors to precisely control the firing of the inverter thyristors. This forced commutation of the inverters allows high torque to be used at starting with only 1.4 times the continuous rated power of the motor. As all eight motors in the train are controlled by separate 3-phase inverters, each drive axle is precisely controlled at all times. This virtually eliminates wheel slip and allows compensation for any weight transfer between drive axles. High voltage train cable While running on the 25kV high speed sections, the rear locomotive has its pantograph raised while the front loco runs with its pantograph lowered. An insulated 25kV cable runs along the length of the train, to feed the transformer primary in the front locomotive. This arrangement is reversed when running in the other direction. As noted previously, when approaching city terminal stations, the TGV trains share tracks with existing electric suburban and regional trains and these run at 1.5kV DC. Therefore the TGV trains need to switch over from 25kV AC to 1.5kV DC. To do this, they coast at 160km/h through a 1.6km section where the overhead wiring has no power. When they reach the 1.5kV DC section, they raise their heavier low voltage pantographs to continue into the city terminal. Records Many records have been set since the Atlantic TGV began running from Paris to Le Mans on 24th September, 1989. It was the world's first to carry passengers at 300km/h and the regular start to stop average of 224km/h is also a world first. In November 1989, this TGV created an unofficial world speed record of 483km/h (300mph). ~ Acknowledgements Special thanks to Dr John Nicolson of VFT Australia for photographs and data; also to SNCF engineers, to Revue Generale des Chemins de Fer, Dunod and Gauthier-Villars -of Paris. FEBRUARY1990 99