Sorry for my english! Note in my note current refers to the type of current use, characterized by 3 parameters DC/AC and frequency (unit = Hz), intensity (unit = A for Ampere) and tension or voltage (unit = V for Volt). 

 Electricity in France is produced by nuclear power plants (ca. 80% of the production), conventional power stations (fuel, dam on rivers) and renewable energy stations (wind mostly). All plants are ran by the EDF company a former state agency now a private company the stocks of which being however mostly owned by the State.  

 Electricity is transported by a grid-like netwwork owned by RTF (a subsidary of EDF) by main power lines as shown on the picture as 50 Hz AC current at various voltages. Mostly 225 000 and 400 000 V are in use for long distance transport between connecting nods of the grid and/or dispatching centers. A secondary network transports electricity mostly at 63 and 90 kV (all these are regarded as "high tension") to regional transformators that generate "medium tension" (20 and 25 kV) for local delivery or directly for industrial facilities.  Localy, voltage is reduced by transformators to 200V/380V for domestic use. 

 TGV and more generally train lines operating under 25 kV are fed by RTE at various stations (3 on the novel TGV-est (east) line) that reduce 225 000 V to 110 000 volts, next dispatched to sub-stations (19 for this line) that reduce the tension to 25 kV and "inject" this current into the catenary.  

 Hope it helps.