Edit: The Railcolor visitor has been very helpful today and yesterday. We got a lot of answers to our Midi-question. Thank you all! As you can see we recieverd an extra Midi-picture, 427124M in Beziers. This is how it works:
As a first stage, Fret SNCF has asked AKIEM to modify 41 Prima locomotives, so they are compatible with the special conditions, required to run safely on the Midi-lines in the south of France, such as the Bordeaux - Toulouse line (Bordeaux - Hendaye, Bayonne/Dax - Toulouse, Toulouse - Latour de Carol), and Béziers - Neussargues (south of Massif Central). Units involved are BB 27119-137, 142-155, 173-180. Initial tests with a BB 27000 on the midi-network were completed in June 2010. Batch modification is going on right now.
The catenary system on these Midi lines is somewhat different from the other 1500V DC lines in France. This is inherited from the former Midi railway company, that gave birth to SNCF in the late thirties, when the railways in France where nationalised. These lines have a larger 'zigzag', or amplitude. As the number of older locomotives with these collectors are slowly going down, now two-system Prima's need to be adjusted, so that can operate from the North-East of France to Hendaye, at the Spanish border.
On almost all two-system french locos, both pantos have a 1600 mm wide collector, Although of different materials (25 kV AC > two carbon stripes / 1500V DC > eight copper/steel stripes). Having the same dimension, they allow 'emergency operation' with the false pantograph for the system. (Although with restrictions: speed restriction with DC panto under AC catenary / power restriction with AC panto under DC catenary).
This is possible on most of the French Network because :
- AC lines allow 1450 to 1600 mm collectors
- DC lines allow 1600 to 1950 mm collectors
But you see the problem; On a BB 27000M with a new 1950 mm contact on the DC pantograph, the back-up plan does not work anymore. It will cause problems. So next to that, the M's get a software update making it impossible to use the adjusted pantograph under AC catenary. Same for the normal AC pantograph on the DC-Midi lines.
Also these units can run on the complete French network, but without the back-up plan.
Thanks to RV/WFE/DH/AG