These lines use 25 kV AC at 50 Hz. I think compressed air is used to raise and lower the pantograph. In the UK, only the Eurostar passenger trains between London and Paris/Brussels via the Channel Tunnel raise and lower the pantograph in motion. This action occurs at the UK side of the tunnel where the traction supply changes from the overhead 25 kV AC to the third rail 750 V DC used between the tunnel mouth and London Waterloo. When the new Channel Tunnel Rail Link is fully commisioned in a few years time, the high voltage overhead will continue all the way into London (St Pancras).
The shoes that contact the third rail (which is situated on the outside of the running rails) are also raised and lowered as required on the Eurostars. This is because lineside equipment in France (point {switch} motors I think) would be fouled by the lowered shoes. At the French end of the tunnel, there is a simple safety device designed to protect their point motors. A large concrete block is posisiond in such a way as to physically and traumatically remove any contact shoe left lowered.
This may sound a bit dramatic but in the UK in the 1970's a fatal rail accident was caused by a battery cover on a locomotive being left open. This struck a point motor and caused the blades to move under the train. The train overturned with tragic consequences.
