What are the overhead power collection clearances above the highest point of rolling stock and allowing for compact catenary support under bridges and tunnels for 1.5-kv dc & 25-kv ac electrification?
I don’t know but it can’t be much more than the latch down height of the pantograph. They sit on insulators designed so the power doesn’t arc to the carbody. As one used to PRR clearances the pan compression on an IC commuter train always made me nervous.
For common carrier railroad…26’ for 25 kv and above, 24’3 for 25 kv and below…this is above top of rail (railcar height is not as much of an issue)
With light rail equipment, it gets stranger as each entity bends the rules to suit their situation…look at the NEC and AREMA Ch. 33 to play the game. Especially in the approach to grounding bridges of less than the desired height.
I’m not an Electrical Engineer type and so will defer to anyone else who is and has better info - but I’ve been interested in this for a while. It’s hard to find good definitive statements, but here’s a summary of what I’ve come to understand:
‘Rule of thumb’ is about 1 centimeter (2.54 of those in an inch, so it’s a little over 3/8") per 1,000 volts, plus maybe a ‘constant’ of some small amount. So for the PRR’s 11 KV catenary, it can be as little as 11 cm = 4.5", say around 6". See also the photos of the catenary insulator mounts in the ex-PRR, now Amtrak tunnels under the North (Hudson) River into Manhattan, which are pretty ‘tight’ to the roof. Someplace I saw a discussion of how low the ‘graphs are on the SEPTA SilverLiners in the tunnels and at Suburban Station, and amazingly, it was in that same range - OK, about 9" instead - see the lengthy thread, of which this link is to Page 4 of 5, at: http://www.railroad.net/forums/viewtopic.php?f=72&t=57644&start=45 At the bottom of that page, that thread seems to address your question in the context of some SNCF equipment - there’s also some photos someplace else ‘on-line’ of Swiss or Scandanavian tunnels that are set-up for both voltages. I presume the same rule would apply for 1.5 KV DC which would be about 5/8" - say 2", and 10’’ - say 12’’ for the 25 KV AC.
There are also various manufactured insulated boards, strips, or panels that are installed between the Overhead Contact System (“OCS”) and the bridge structure or tunnel roof/ ceiling so that the ‘live’ wire will not ‘ground’ to them. With those, the wire can be mounted almost flush with the structure. One nuance that I’ve come to recognize, esp. with single-track arched-roof tunnels: The outer ends of the ‘horns’ on the pantographs are also ‘charged’ or 'li
Sounds pretty good, Paul; and gives me some idea. I was aware of the arched roof and track curve cant issues as well. My focus on minimums is for tight locations for segregated regional and intercity passenger trackage.
Another issue seems to be vertical curves. The Metra Electric has some 50 mph speed restrictions passing under low railroad viaducts on tangent track. I imagine the bottom curve would present a problem for the panograph to react quickly enough at higher speed.
Also, how the heck can there be a smooth curve in the contact wire instead of an abrupt change? Is that just a combination of length of the vertical curve radius and weight of catenary; or is there a trick?
The Philadelphia City Center railfan discussion didn’t help much.
For Metra Electric bi-levels with a 15’10" roof height, the contact wire may need to be nominally 16’2" to allow for ~3" bounce, sag, and track irregularities for 1.5-kv @ 5/8" per 1-kv… Would it be accurate to assume that going to 25-kv may require a nominal 22" air gap assuming the rating is for the rms voltage of alternating current? The resulting wire height would need to be 17’11" and 19’9" to the bottom of overhead structure.
As I recall the 25kV catenary at Summit (on the DL&W main in NJ) is 17-0 above top of rail; no idea whether it gets any lower than that elsewhere.