French State Railway CC 70000

The class CC 70000 designated two diesel locomotive prototypes which were intended to replace the most powerful steam locomotives. The highest possible power output was to be achieved by combining two diesel engines with an electric power transmission. The four-axle diesel-hydraulic BB 69000 of 1963 already had two Pielstick 16PA4 185 rated at somewhat over 2,000 hp each. The new locomotives from 1965 had both engines set at their maximum of 2,400 hp and needed a total of six axles due to their electric traction equipment.

Instead of giving each engine a separate generator, both worked onto the same generator. This one did not have a stator and a rotor, but had two rotors. When each engine rotated one rotor in opposite directions at its maximum 1,500 rpm, this created an effective speed of 3,000 rpm. This in turn allowed for a more powerful generator for the same size.

The bogies were similar to those of the electric CC 40100. They had one large traction motor each that powered all three axles at the same time. Like most French monomotor bogies, they allowed to switch between two gear ratios for a top speed of 85 or 140 km/h. CC 70002, the second prototype, could even change its gear ratio on the move at low speeds. But sadly, this feature was the cause for many problems.

After CC 70001 was delivered in December of 1965 and CC 70002 in July of 1966, they were initially tested in freight and passenger service. Due to many problems in the electric part, apart from the transmission problems of the second locomotive, they were not very successful. In the end the one-engine CC 72000 with only one diesel engine of 3,600 hp was more reliable and was thus selected for series production. CC 70002 was already retired in 1973 and CC 70001 was used in freight service only until 1983.