How fast can trains using third-rail traction go?
Some people say 90 MPH on the LIRR. Others say less. Does over- and under-running make any difference?
In 1977 I was aboard a late Jamaica to Penn Station train which was filled with fans from a trip to Montauk. A stop watch to the mile posts indicated a litte over 100 mph. So, I would say, we don’t know how fast they really could go. We do know that cat electrics go faster, that diesels are capable of more, and that given the right circumstances (straight away, unlimited steam supply) a steam locomotive some say is unlimited.
MNRR and LIRR both have set speeds over ninety but below 100. Capability of equipment and engineer is the next dependent thing.
I am certain that third rail electrics can be designed to match the speed of any catenary electric, but that does not mean it will be done.
The limitation is the voltage, High speed trains, really high speed, all use very high-voltage transmission because of the power involved. 12,500 or 11,000 volts seems minimum, as with Acela. The Euopreans and Chinese are all 25,000V like New Haven north to Boston on Acela and other NEC trains. Haqving that kind of voltage on a third rail would result in shorts, because of the short distance from third rail to ground rail, the running rails.
But one could design high speed trains using 1000V DC or 700V AC which would be safe with third rails, but nobody seems to want to go that route.
There is nothing inherently better about a pan rubbing along a wire than a third rail shoe rubbing along a third rail. Except for better opporunity for far better insulation.
The only caveat I have Dave is that it is better to have a pantograph under high voltage/Lower current break contact, rather than a Third-rail Shoe with Low Voltage/High Current, if say the vehicle bounced on its springs due to track irregularities.
Both problems can be handled by bussing the power as the Reading did. However, that may make problems at section breaks, requiring a neutral non-powered floating section. The real problem is the high power with third rail and low voltage means huge current and thus a substation every half mile or mile or wads of expensive copper feeder cable paralleling the third rail and the ground return of the running rails, both very expensive. 11000 volt electrification means a substation eveyr ten to twenty-fiv emiles, and at 25,000 volts it can be 25 to 60 miles. Lots of savings there.
Might be worthwhile crunching a few numbers.
Short term power draw for an AEM-7 would be ~7 MW, which would be close to 12,000A at 600V or a bit more reasonable 6,000A at 1200V (Central California Traction used 1200V third rail for many years). With that, the third rail shoes would have to be fairly stout to handle the current, which would entail a higher contact pressure to maintain contact at high speeds. Using MU cars would allow current collection to be spread over more shoes, but there would still be a limit on how much current the rails an conduct - recall a limit of 14,000A for the NYC Grand Central electrification and about the same for the NY subways.
- Erik
YOu are correct that high speed with third rail would definitely require mu operation, because of the limite on sintgle shoe current pick-up. 1200V CCT was definitely the highest volage ever used on third rail. That would allow spacing substations abouit every four miles, some improvement but not enouigh. Mx for AC would be 840V That would give about 1200 peak to ground which is what the insulaton must be rated for.
Minor correction, CCT’s 1200V was the highest voltage successfully used on third rail, the Michigan Railways had a problematic time with 2400V third rail operation and gave up after a short time.
- Erik
Those figures give me a new appreciation for the NYC electrification. In the 60s I sometimes rode the Harlem line starting out in diesel territory. Commuter trains might have had a dozen heavyweight cars pulled by a couple of RS-3’s. At North White Plains (then the north end of 3rd rail) the Alcos came off, and a P-motor with a couple more coaches would couple on, to haul the whole thing to GCT, with all power conducting thru 1 or 2 third rail shoes (though it was not what you would call high speed operation).
In fairness, a pair of RS3’s would be rated at 3200 HP, while the rebuilt P-motor had a continuous rating of 4243 HP.
The number I always heard floating around the old PC guys, who should know this stuff, early in my career was 100 mph. Beyond that, there were problems keeping the shoes in solid contact with the rail. The shoe would start bouncing.
I suppose you could design a more complicated shoe spring system with some damping to keep the shoe nicely in contact, but there was (is?) no demand for it.
I don’t find it hard to believe that the LIRR ran close to 100 mph. I recall riding a south shore line train of M1s the early 1980s that was easily over 90 mph.
In the UK speeds of up to 100mph are allowed (and reached) on the third rail (BR Southern as was).
The class 92 electric locos (for Channel Tunnel traffic) are rated at 5360hp on 3rd rail (750v dc) (more on 25kv ac overhead) - they are Co-Co’s with twelve shoes (six each side).
The French had one line (in the Alps) which for many years had 1500v dc third rail.
As I indicated, my first (known) 100+mph experience was with LIRR in 1977 going west from Jamaica when the fan group pulled out stop watches and proclaimed to be going just over a100. So 3rd rail 100mph is possible here in the states, the question is therfore, is it sustainable or useable?
The world speed record for third rail traction is held by a British 442 multiple unit at 108mph. In normal operation, these units were limited to 100mph. Much of the rail south of London is electrified with the third rail system (750V DC) and the majority of modern units are rated at 100mph. This is not achieved all that often on most routes, however, as this is commuter territory and the distances between stations are not that great.
There used to be a side-contact 1200V DC third rail system linking Manchester to nearby Bury. It is now part of a light rail system and uses overhead catenary.
The Eurostar locos that run through the channel tunnel are true high-speed trains running at up to 300kph (186mph). When the London terminal was Waterloo, they used 3rd rail on the British side of the tunnel, where they were restricted to 100mph. Now they have a dedicated (25kV AC overhead) line to the new terminal at London St Pancras and the 3rd rail equipment has been removed.
What I was really trying to get at was the thousands of amps going thru 2 third rail shoes, or only 1 shoe at gaps.
According to the Hilton-Due book on interurbans railways, the Michigan Railway (an interurban) tried to operate its 1915 Grand Rapids -Battle Creek-Kalamazoo-Allegan (Michigan) extension with a 2,400 volt DC third rail. It was not a sucess. Among other problems, the current would arc between the third rail and the journal boxes. The danger was from the current was thought to be so great that waiting passengers had to be kept in locked loading pens, which the conductors unlocked when their trains arrived. It was converted to 1,200 volts after about a year.
Again, I agree with you about pantograph at high voltage vs shoe at high current. The shoe problem could be solved by a train power bus, with fat jumpers between cars. But still, substations every few miles? Not practical.
Really what is the point, high speed rail everywhere is doing just fine with catenary. All future plans for HSR or HrSR will be with catenary so who needs third rail at high speed?
Long Island might want the option, as they push their existing 3rd rail further out onto the island.
Although the “official” world speed record for third-rail traction may be 108mph, I know of at least 2 authoritative records of British Class 442 units achieving 117mph, and I personally recorded 111mph with their predecessors as long ago as 1976. However, with today’s strict monitoring, speeds significantly above the 100mph limit are almost unheard of.