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Discussion relating to the operations of MTA MetroNorth Railroad including west of Hudson operations and discussion of CtDOT sponsored rail operations such as Shore Line East and the Springfield to New Haven Hartford Line

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 #1591612  by Yellowspoon
 
I was watching a YouTube video taken from Pelham station during evening rush hour. The video inspired me to ask the same question as the OP. That led me to this 2015 thread, which answered why the changeover moved. After reading about the crash in 1988, I wonder if the crash affected the decision to move the changeover point. I have follow-up observations/questions.

By my calculations, there is an 800m (one half mile) section of track with both third rail and catenary. I had always assumed that trains changed power source during this overlap. However, of the 20 +/- trains in the aforementioned YouTube video, all but one had no source of power for a brief period during the 400m (one quarter mile) between Pelham station and the third rail. (i.e. eastbound trains did not raise the pantograph until the last car was clear of the third rail) The only exception was one GCT bound train that did not lower the pantograph until the first car was on the third rail.

Two follow-up questions: (1) At some point the video there is a GCT-bound diesel pushing eight passenger cars. None had pantographs. I assume the engine has shoes for the third rail. Where is it coming from? I assume it’s not Amtrak. (2) Earlier poster in this thread talked of a “phase gap” at Pelham. What is a phase gap, and does the train operator do anything at the phase gap.

As a trivia point, I was once on a NH bound train that stalled at/near/during the changeover at Woodlawn. We sat there for about 45 minutes until another train pulled up beside us and all the passengers “walked the plank” to the other train. I’m going to assume now that all trains have a plank or board for just such an occasion. I remember that my then-teenage daughter was a bit nervous because our train was listing to the right. She was afraid that the train might tip over until I told her about the fact that we were on a curve and would not have noticed if we had been going 30 MPH.
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 #1591645  by shadyjay
 
Yellowspoon wrote: Fri Feb 11, 2022 3:10 pm Two follow-up questions: (1) At some point the video there is a GCT-bound diesel pushing eight passenger cars. None had pantographs. I assume the engine has shoes for the third rail. Where is it coming from? I assume it’s not Amtrak.
If there's a diesel pushing traditional coaches, it could've been either a Danbury-to-GCT rush hour express, or a New Haven-to-GCT train. Most NHV-GCT trains are M-8s but I have seen reports of some using diesels and push-pull equipment, especially late at night. Diesels remain on diesel power until somewhere around 125th St Station, then they switch to third rail power. I'm not sure if that practice happened with the FL-9s on the NHRR, though theoretically they could run on third rail power (the New Haven's electric locos had to run off third rail beyond the Woodlawn changeover).
(2) Earlier poster in this thread talked of a “phase gap” at Pelham. What is a phase gap, and does the train operator do anything at the phase gap.
I believe it signifies a change in voltage. On board, there is a temporary power drop... more noticeable on Amtrak since there's just one pantograph, vs several on the M-8s.
 #1591675  by west point
 
Phase gap or in the case of the PRR terminology phase break can mean of one of two reasons. Breaks in AC CAT can mean either a different source of power or maybe taking power from another phase of the power. For PRR CAT that just means taking power from the other end of the power since PRR is single phase like your house. (110/110 = 220). So PRR is 12k / 12k = 12k after transformers.
 #1591680  by west point
 
Another point about AC phase breaks. The gap has to wide enough for dual pan electric locos and EMUs that can be supplied from more than one pan is not possible. Seems like I remember that Amtrak had a train that stalled at a phase break on a bridge. Never heard reason if the phase break was too long for the Amtrak loco or if it could not raise the other pan? Might have been longer for MNRR EMUs?
 #1591985  by Ridgefielder
 
The 3rd rail is 750V DC. The catenary is 12.5kV AC. The trains can't (obviously) take power from both so they need to coast while making the changeover.

Remember, steel wheels on steel rails = very little friction. Trains can roll without power for a decent distance and the infrastructure is designed with that in mind. For example, there is no catenary on the draw span of the Cos Cob bridge over the Mianus River in Greenwich-- trains have been coasting through that gap since the line was wired back in 1907.
 #1592160  by Yellowspoon
 
That would make sense, but . . . What's the point of the 800m overlap where there is both third rail and catenary? Also, there is no doubt in my mind that there is hardware/software on the train that prevents cross-feed should the operator accidentally raise/lower the pantograph too early/late. There was one train in the aforementioned video that did not lower the pantograph before the first car was connected to the third rail.
Last edited by nomis on Sat Feb 19, 2022 2:40 pm, edited 1 time in total. Reason: Removed immediate quote
 #1636222  by bulk88
 
shadyjay wrote: Fri Feb 11, 2022 10:24 pm I believe it signifies a change in voltage. On board, there is a temporary power drop... more noticeable on Amtrak since there's just one pantograph, vs several on the M-8s.
AEM7s, HEP (fans, 120v convenience outlets) goes out, on every last phase gap. A strong breeze can make the wire bounce and HEP goes out for a second. Sprinters, automatically regenerate HEP (brake) for a couple seconds on each phase gap, fans and 120v never goes out on amfleets behind a Sprinter. M2-M6s/M8s had/have MGs, or capacitors, or atleast 120v is on battery for a couple seconds before load shedding. M8s also have the anti-wire down, emergency rapid panto-drop if zero voltage thing, I think the M8's emergency panto drop software has been tweaked over the years to not be as aggressive as day 1 of M8s. M8 S cars, because 1 car of shoes, not 2, on 3rd rail, oh boy, like half the Harlem line in an S car has no 120v for charging phones/laptops. But I try to ride in S cars if I find them, quieter ride :-D

Did AEM7s use inverters for HEP and 120v or online tap changers, and secretly deliver 25 hz @ 120v to your cellphone?

Brushed AC motors don't care about HZ, and LV DC consumer electronics don't care about hz. Only AC induction motors would act funny on 25 hz.
 #1636223  by bulk88
 
west point wrote: Sat Feb 12, 2022 2:58 pm Another point about AC phase breaks. The gap has to wide enough for dual pan electric locos and EMUs that can be supplied from more than one pan is not possible. Seems like I remember that Amtrak had a train that stalled at a phase break on a bridge. Never heard reason if the phase break was too long for the Amtrak loco or if it could not raise the other pan? Might have been longer for MNRR EMUs?
2, 4 and 5 car New Cannons were a long policy debate vs cos cob bridge. PTC/ATC/event recorders slowly made the Cos Cob bridge more and more of a mouse trap. 2000s I think 6 or 7 is NHL minimum policy unless its the shuttle. Old days, TO could just break the rules and go full throttle into the bridge, and mushroom if obstruction ahead. Not sure if Cos Cob old days, had Approach Limited signal heads, and you stop before the bridge, but with cab signals, you can stall on the bridge, since by the time cab signal aspect drop, its too late to stop before the bridge. Spuyten Duyvil supposedly changed ATC cab signals from diverge/conflict, to general MAS enforcement, and cab signals after Spuyten Duyvil can't be used to separate MAS enforcement from conflict anymore.