AGV: the next generation: AGV, the world's newest and fastest high-speed train, was unveiled at Alstom's plant in La Rochelle, France, on February 5 by President Nicolas Sarkozy of France. Alstom's faith in its new train has already been rewarded with a contract for 25 trains from the world's first open-access high-speed operator, reports David Briginshaw from France

International Railway Journal, March, 2008 by David Briginshaw

THE roll-out of the first AGV is the culmination of 10 years of development work by Alstom and a major tribute to its faith in the future. The decision to go ahead with AGV--Alstom's fourth generation of high-speed trains following on from the successful TGV family--was taken in 2003 when the company faced a major financial crisis.

"We developed AGV at our own expense and at a time when Alstom was going through a very troubled period because we wanted to ensure our future," says Mr Patrick Kron, Alstom's chairman and CEO. AGV was also developed without any client-imposed specification, which Alstom describes as a "radical step in the railway industry."

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AGV represents several major advances in technology over both TGV and other types of high-speed train, and a number of key objectives guided its development. The maximum commercial speed of AGV has been increased to 360km/h from 320km/h for TGV, while trying to match or better TGV's environmental impact and operating costs. AGV is Alstom's first 300km/h tram with a distributed traction system obviating the need for traditional power cars, but while retaining TGV's trademark articulation. This increases usable floor space by 20% (over the same train length) and makes it possible to have greater flexibility in the number of cars per train.

"AGV is the fruit of a major technological breakthrough as we have combined articulation with powered bogies," says Kron. Alstom was determined to retain articulation in AGV as it believes this has been fundamental to TGV's excellent safety record--the ability of the train to remain upright in a derailment--as well as its stability and good ride comfort: articulation means the passengers do not ride over the bogies.

Articulation also reduces the number of bogies required per train. A TGV has five fewer bogies than other types of 200m-long high-speed train and AGV saves another bogie. Fewer bogies mean a lower first cost, less weight, less air resistance, and reduced maintenance costs--a bogie can account for 35 to 40% of the cost of maintaining a coach because of the number of parts with high rates of wear.

New technology

The development of synchronous permanent magnet motors makes it possible to power an articulated high-speed bogie for the first time. A permanent magnet motor occupies about one-third less space than an asynchronous motor, so it can fit within the bogie rather than being suspended from the car body as with TGV. This lowers the centre of gravity and makes it possible to reduce the floor height by 100mm, which means only two 20cm-high steps are needed to board AGV from a French station platform.

The permanent magnet motor has other advantages too: a power to weight ratio greater than 1kW/kg compared with 0.8kW/kg for other types of motor, and it has 98% efficiency compared with 96 or 97% for an asynchronous motor which, coupled with a simplified drive train, should result in AGV consuming 6 to 7% less energy than TGV.

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"The permanent magnet motors are completely enclosed which will prevent dirt ingress," says Mr Laurent Baron, Alstom's AGV platform director. "We are still discovering the great potential with this new technology."

The AGV bogie uses composites as well as steel to produce a weight saving of 1 tonne per bogie. Overall, AGV will weigh 10 to 15 tonnes less than TGV. Moreover, as Mr Francois Lacote, Alstom's technical director, explains: "the amount of noise produced by an AGV motor bogie is lower than that of a TGV traction bogie and about the same as that of a TGV trailer bogie."

The AGV bogie and traction system have been tested extensively and as part of the world speed record trials last year. "Everything that could create problems has been tested," says Mr Phillipe Mellier, president of Alstom Transport.

According to Alstom, a high-speed train will generate twice as much noise at 330km/h than at 300km/h. However, by improving the aero-acoustics of AGV and particularly for the end cars by refining the nose design and adding air deflectors to the bogies, Alstom claims that an AGV travelling at 360km/h will have the same level of noise inside the train as a TGV travelling at 320km/h.

Traction triplets

AGV's traction system is based on groups of three cars, consisting of two powered cars and a transformer car, plus a car with auxiliary equipment in between two triplets. The minimum train length is therefore seven cars (132m long with 245 seats). Alstom says there is no limit on train length, although few operators would want to go beyond a 400m-long train. An 11-car AGV would be 200m long with 446 seats, which is only 70 seats less than a 200m TGV Duplex double-deck train with 516 seats. An 11-car AGV fitted with six motor bogies would generate a power output of 22.6kW/tonne.

The maximum speed of AGV is determined by the braking capability of the train with one bogie's braking system out of action. This means that a seven or eight-car AGV would be restricted to 300km/h, a 10-car train to 320km/h, and only trains of 11 or more cars will be able to run at 360km/h.