blue streak 1 DMUinCTAmtrak has Constant Tension from New Haven to Boston, the Acela's 150 mph zone. Also MN's CAT that has been replaced from New Haven to New Rochelle, AMTRAK New Rochelle - Harold interlocking:, NJ Transit's M & E, Boontown, & NY&LB routes. Also many new light rail systems; Baltimore, San Jose, Sacremeno, San Diego, etc.
DMUinCTAmtrak has Constant Tension from New Haven to Boston, the Acela's 150 mph zone.
Also MN's CAT that has been replaced from New Haven to New Rochelle, AMTRAK New Rochelle - Harold interlocking:, NJ Transit's M & E, Boontown, & NY&LB routes. Also many new light rail systems; Baltimore, San Jose, Sacremeno, San Diego, etc.
Sorry to say, Metro North Commuter Railroad has (is) replacing the 100 year old Catenary with a late model design for 90mph service. For the most part, Constant Tension was not added do to reuse of the old towers. Plenty of speed for MUs and Commuter Trains but "slow orders" for the 20 Acelas that ply that section of the Corridor.
Don U. TCA 73-5735
As stated, the Carbon Strip on the Pantograph provides lubrication. With the Acela, it's inspected often for ware and breaks.
Constant Tension Catenary gets its name by holding a constant height AND tension. The Contact Wire and Support Wires expands and contracts day and night, Summer and Winter. If strung tight in the Summer it could contract and break in the Winter, also, there would be little "give" from the pressure of the Pantograph(wear) . If strung tight in the Winter, the Catenary would "sag" in the summer and move up against the Pantograph pressure. In the past, multiple suspension wires were used to hold the Catenary rigid, remember the New Haven Trianglar Catenary?
Constant Tension Catenary solves the problem by cabling from the support wires to weights located on the Mast. The Slack is now pulled sideways keeping the height and tension constant. The distance of the pull varies with temperature. Amtrak has Constant Tension from New Haven to Boston, the Acela's 150 mph zone.
The only method that I'm aware of is in the actual construction of the CAT. The old NYNH&H, PRR, & RDG CAT was constructed basically on a straight line from hanger to hanger. Very little deviation of the contact wire from the center line of the track was constructed. If you now look at the present day modern constant tension CAT the wire will move 10 - 14 inches from side to side. (ride or observe any of the current new light rail systems and you will see this back and forth on the pans. Mainly this was to prevent the wire cutting a grouve in the contact carbon on the pan but would appear to allow cooling when not contacting the wire, Watch the video of the TGV speed record attempt and there are snipets showing this back and forth.
I'm no expert, but there are a couple of factors involved. The pantograph shoe has an insert of a carbon paste strip which actually contacts the wire. This provides actual contact to draw the current and also acts as a lubricant (think graphite). The pantographs are also of light weight and the spring tension that keeps them raised provides for a light pressure against the overhead wire.
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