The TGV (train à grande vitesse, 'high-speed train') holds a series of land speed records for rail vehicles achieved by SNCF, the French national railway, and its industrial partners. The high-speed trials are intended to expand the limits of high-speed rail technology, increasing speed and comfort without compromising safety.
The current world speed record for a commercial train on steel wheels is held by the French TGV at 574.8 km/h (357.2 mph), achieved on 3 April 2007 on the new LGV Est.
The TGV 001 was an experimental gas turbine-electric locomotive-powered trainset built by Alstom to break speed records between 250–300 kilometres per hour. It was the first TGV prototype and was commissioned in 1969, to begin testing in 1972. It achieved a top speed of 318 kilometres per hour (198 mph) on 8 December 1972.
Operation TGV 100, referring to a target speed of 100 metres per second (360 km/h, 224 mph), took place on 26 February 1981 shortly before the opening of the LGV Sud-Est and ended with a speed record of 380 km/h (236 mph) set by TGV Sud-Est trainset number 16.
Operations TGV 117 and TGV 140, referring to target speeds in metres per second, were carried out by SNCF from November 1989 to May 1990. The culmination of these test programs was a new world speed record of 515.3 km/h (143.1 m/s or 320.3 mph), set on 18 May 1990.
In the early stages when operation TGV 117 was still being defined, several criteria were settled upon to focus the preparation of a test train. These were aerodynamics, traction and electrical systems, rail and catenary contact, braking, and comfort.
The basic purpose of the test program was to push the envelope of the TGV system, and to characterize its behavior at very high speeds. With this in mind, it only made sense to start with a stock TGV trainset and to modify it as little as possible. Brand new TGV Atlantique trainset number 325 (25th of 105 in the Atlantique series) was arbitrarily chosen to be the starting point of the modifications. There was nothing special about this trainset, and it was returned to its intended state after the test program to enter revenue service. Today, the only distinguishing feature on 325, as compared to other Atlantique trainsets, is a blue ribbon painted across the nose, and bronze plaques bolted to the sides of the two power cars to commemorate the event.
The record runs took place in two separate campaigns, separated by a period of modifications to trainset 325. For each day of testing, the 325 was towed to the test site by TGV Atlantique trainset 308 because its 1500 V DC systems had been removed, preventing operations near Paris. Trainset 308 also performed a sweep of the test track at 350 km/h before each high-speed run.
The test runs took place on a section of the Atlantique branch of the TGV network, a few months before the line was opened to TGV revenue service. Strictly speaking, there were no significant alterations of the track or catenary for testing purposes. However, some sections of the line's profile had been planned since 1982 (shortly after the TGV Sud-Est world speed record of February 1981) to allow very high-speed running.
Construction of the dedicated tracks of the LGV Atlantique was officially decided on 25 May 1984. Ground was broken on 15 February 1985. The new line was to stretch from slightly outside the Gare Montparnasse in Paris to Le Mans, with a second branch towards Tours. The Le Mans branch was opened for 300 km/h (186 mph) revenue service on 20 September 1989, and the Tours branch opened a year later. The two branches separate at Courtalain, 130 km west of Paris, where movable frog points good for 220 km/h (137 mph) in the diverging route direct trains towards either Le Mans or Tours.
The test section itself begins on the common branch, at kilometre 114, at the Dangeau siding. It runs past Courtalain and onto the Tours branch of the line. Between kilometre 135 and kilometre 170, the line was designed with progressively wider curves, reaching a minimum radius of 15 km (9.3 mi) after kilometre 150. These curves were built with larger superelevation than strictly necessary for running at 300 km/h (186 mph). At kilometre 160, the line passes through the Vendôme TGV station. At kilometre 166, there is a long 2.5% downhill stretch into the Loir valley (the Loir is a tributary of the better-known Loire river) and the line crosses the Loir on a 175 m (575 ft) bridge. This is the area where the highest speeds were expected, and most of the activity was concentrated there.
The Tours branch of the line was tested by special computerized Maintenance of Way equipment manufactured by GEISMAR, from the Track Research department of SNCF. Just as on all TGV lines, the rails were aligned to 1 mm (0.039 in) tolerances, and the ballast was blasted to remove small, loose gravel. In subsequent testing with trainsets 308 and 325, the track was not significantly affected and required only minimal realignment. This was in contrast to the 1955 world speed record of 331 km/h (206 mph), also set in France, where the track was seriously damaged after the high-speed runs. Large sections of the track were warped and misshapen, as well as the train's pantograph was melted. Strain gauges were placed in several locations, especially at the expansion joint at the end of the Loir bridge.
The catenary was standard TGV style, without any modifications. The only changes were in the tuning. In general, when a pantograph passes under the catenary, it creates a wave-like disturbance that travels down the wire at a speed determined by the tension in the wire and its mass per unit length. As a train approaches this critical speed, the pantograph catches up with the disturbance, causing dangerously large vertical displacements of the wire and contact interruptions. The maximum speed of the train is then limited by the critical speed of the overhead line. This problem was central to the test runs, as it was desired to test the 325 set at speeds well above the critical speed of the standard TGV catenary. There were two solutions: increase the tension in the wire or reduce its mass per unit length.
The TGV catenary is strung in 1,200 m (3,900 ft) sections and mechanically tensioned by a system of pulleys and counterweights. The masts are spaced at 54 m (177 ft) apart. The messenger wire is bronze with a circular cross-section of 65 mm2 (0.101 in2). The contact wire is copper with a cross-section of 150 mm2 (0.23 in2). The cross-section of the contact wire is circular with a dovetail cut at the top.
Replacing the copper contact wire by a lighter cadmium alloy wire was considered, but dismissed on the grounds of time and cost. The critical speed of the test track catenary was then to be increased solely by increasing the tension in the wire. For the test runs, the usual tension of 20 kN (4,500 lbf) was increased to 28 kN (6,300 lbf) and exceptionally 32 kN (7,200 lbf). For some of the faster runs over 500 km/h (310 mph), the voltage in the catenary was increased from the usual 25 kV 50 Hz to 29.5 kV.
At kilometre 166, catenary masts were equipped with sensors to measure the displacement of the wire. During the 18 May 1990 record at 515.3 km/h (320.3 mph), vertical displacements of almost 30 cm (1 ft) were recorded, within 1 or 2 cm of the predictions made by computer simulations. The critical speed of the catenary for that particular run was 532 km/h (331 mph).
Preparation of the train for Operation TGV 117
In preparation for the first round of testing, modifications began by shortening the train from its usual 10 trailers to only 4 trailers, resulting in a significant increase to its power-to-weight ratio. The resulting train consisted of: power car TGV24049, Trailer R1 TGVR241325, Trailer R4 TGVR244325, Trailer R6 TGVR246325, Trailer R10 TGVR240325 and power car TGV24050. Train length was down to 125 m (381 ft.) from 237 m (777 ft) and weight was down to 300 t from 490 t.