AGV: The Next Generation - high speed trains

International Railway Journal,  May, 2000  by David Briginshaw

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Alstom in cooperation with French National Railways (SNCF) is developing a new design of TGV called AGV. It will be the first articulated high-speed train with distributed traction rather than power cars at each end. Prototype AGV cars are under construction and should be ready to start testing in March 2001.

THERE are a number of reasons why Alstom is keen to develop the AGV, which stands for Automotrice [acute{a}] Grande Vitesse. It perceives a commercial need to increase the maximum speed of TGV from 300 to 350km/h but with the same operating performance and cost as a 300km/h train. Advances in technology now make this possible. AGY will have 9% more capacity within the same length of train (200m) than a conventional TGV.

AGV will combine the best elements of TGV and things such as eddy current brakes developed for the former TGV New Generation project, and introduce distributed traction. This would enable Alstom to meet the recently-announced aspirations of the president of French National Railways (SNCF) and the chairman of German Rail (DB) to draw up jointly specifications for the next generation of high-speed trains to reduce development and procurement costs (IRJ February p3). Alstom is keen for AGV to be a contender for the new TGV Est Europ[acute{e}]en project (see following article).

Alstom will bid for the contract to supply between 26 and 40 trains to Spanish National Railways (Renfe) for the new Madrid-Barcelona high-speed line (see World Report). "Renfe would like to achieve a 2h 15mm journey time for the 651km Madrid-Barcelona trip to compete effectively with air," Mr Georges Palais, Alstom's high speed product manager, told IRJ in Paris. "We could achieve this with 350km/h operation, with an allowance for recovery time."

The key element from TGV which will be retained in AGV is the articulation and the articulated bogies, as palais explained. "The goal is to conserve the articulation because of its excellent ride characteristics and good safety record." The articulation performed well in two derailments involving TGVs. The trains remained upright and in alignment with track.

Distributed power high-speed trains are not new. The Japanese Shinkansen family of trains has always had distributed power, as has the Italian Pendolino, and now ICE 3, the latest generation of German high-speed train. However, as Palais pointed out, "it has only recently become possible to marry distributed power with articulation while keeping within the 17 tonne axleload restriction, which is the European standard." This is thanks to the advent of new power semi-conductors of the IGBT type. "The potential gains in mass resulting from this type of component now mean that it is possible to design an articulated train capable of operating at speeds in excess of 320km/h," Palais said. AGV will therefore have Alstom's Onix IGBT traction system. However, technology has not advanced enough yet to allow a double-deck AGV.

AGV train configurations will be based on a module of three coaches with two powered bogies (each axle driven by a 600kW asynchronous motor) and a trailer bogie. This makes it possible to produce various formations which each have virtually the same traction and braking performance. Thanks to the variable sizes of traction equipment, it is possible to add non-powered trailer coaches to permit seven, 10, and 14-car trains. There will be only two types of coach: one with a driver's cab and an intermediate coach.

The result is that a 200m-long 10-car AGV will have only 11 bogies compared with 13 on a 10-car TGV R[acute{e}]seau set (two power cars and eight trailers), which should reduce rolling noise. AGV will seat 411 passengers compared with only 377 in a TGV R[acute{e}]seau, so the cost per seat should be less with AGV.

AGV represents a number of technical challenges. As Palais was quick to point out: "It would be unthinkable to increase the operating speed while at the same time reducing the level of dynamic comfort in the trains or imposing additional stresses requiring increased track maintenance. Any increases in speed must be achieved while offering the same level of comfort as that obtained with TGVs running at 300km/h on the same quality of track."

Alstom has therefore developed an active lateral suspension system, which will be fitted to each trailer bogie, to stabilise the coach laterally in relation to the movement of the bogie on the track. An electric actuator will maintain the coach body virtually within the axis of the bogie thereby avoiding contact with the stops. This recentring will make it possible to soften the secondary suspension which should increase comfort during alignment. The electric actuators will be controlled to stabilise low and medium frequency lateral movements of the car body in relation to the bogies. In addition, the level of comfort does not vary according to the position of the coach in the train.

Alstom has fitted active lateral suspension and electric actuators to a TGV R[acute{e}]seau and tested it at 350km/h on the Lille-Calais section of TGV Nord Europe. The dynamic comfort at 350km/h matched that of a non-equipped train at 300km/h. Another set of tests will be conducted next month with a modified design of actuator.