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Thread: Electric Locomotives - Prototype Practice Question

  1. #1
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    Default Electric Locomotives - Prototype Practice Question

    In developing physics behavior for OpenRails a question has come up. Consider a train with an electric locomotive on one end, and an unpowered unit with a driver's position at the other end.

    My questions are regarding the ampmeter in the unpowered driver position.

    1. Would there be an ameter in the driver's position of an unpowered car?
    2. Does that ameter show the current draw of the powered unit - I assume transmitted through the MU connections?
    3. If there is more than one powered unit in the train, would the ameter show only the current draw of one of them, or all combined?

    Any input would be helpful.

  2. #2
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    I'd offer some insight into at least question 1:

    The older the equipment, the less likely there would be a display like that in a "cab car". I can point to some existing, in use, equipment (ex-Metroliner Cab Cars for instance) that are used as electric push-pull operations (the Amtrak "Keystone Service" for instance) that don't have an ammeter in the Cab Car cab. I believe they do have "wheel slip" and other warning light indicators though, and that those apply to the locomotive, not the cab car.

    Now, having looked into new push-pull cars, like the NJT Multilevel cab cars, I've noted that they have "multi-functional displays" - digital screens that I know, at least on other equipment, are capable of displaying Ammeter type information. Whether they do or not, we'd have to research.

    If a cab car had an ammeter like a locomotive, I have to imagine the only relevant information that an ammeter should display would be the traction motor current of the locomotive/power unit.

    Now to further muddy the waters... some EMU equipment, (whether a powered unit or an unpowered trailer/cab) never had any sort of ammeter at all. Cars like the PRR's MP54s and Reading MU's (referred to in later years as "Blueliners") never had an ammeter in the cab of even powered units. Newer cars such as the PRR's Budd and St. Louis Silverliners (IIs and IIIs), the Jersey Arrow Is, and even the Arrow IIs and IIIs, as originally equipped, did not have an Ammeter or Load Meter. The LIRR M1 "Metropolitans" and the SEPTA Silverliner IV DID have a "Load meter", as do the brand new Silverliner V's and it occurs to me that all are/were equipped with Dynamic Braking, which may have been the reason.

    I would suggest that if the OR team is considering whether to allow an Ammeter type function in an unpowered cab car, that they DO include the option to have one. I'd recommend having the ability to have ANY locomotive type gauge/display function in a cab car, just as in a locomotive.

    Steve

  3. #3
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    I appreciate the insight.

    So if we do allow for an ammeter in an unpowered car, and there is more than one powered loco in the consist, would it display the sum of the current for all locos, or perhaps the average current?

  4. #4
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    That's a little trickier - if you have a multi-unit locomotive lashup, wouldn't the locomotive with the leading cab only display current from it's own traction motors? I don't think it would be combined current, I'm not sure that information would be helpful. (ultimately, you'd want to display current to make sure you weren't burning out a traction motor - a combined current wouldn't do that, IDEALLY, you'd want current information from EACH traction motor, some might run "hotter" than others) However, the question in my head is that IF it is displaying information from only one locomotive in a cab car which locomotive should it display? Perhaps with more advanced displays, the driver would have the option of selecting from which unit to display traction motor current (I'm looking at my ALP46 manual, and I see that the multi-function display has the ability to display information from other locomotives in a multi-unit set, so perhaps a display like that in a cab car would be able to do that as well - select which unit to display).

    I wonder if that's something that the locomotive or cab car creator could specify in OR - like which locomotive to use? But how would one specify it? By a locomotive number (thinking, like it's position in the consist - closest one would be 1, then on back 2, 3, etc). But maybe that's going overboard?

    It just makes me wonder if the physics of the electric locomotives will be so finely determined that one will even be able to see a difference in traction motor current between two locomotives (assuming same type, obviously different locomotives could have different motor currents) - or for that matter, in the current between different traction motors on the same locomotive (which would be the case in real life due to a host of differences). Of course the same logic applies to dynamic or regenerative braking current...

    Now I'm seeing why you're puzzling about this...

    Steve

    {I think Joe Realmuto should get in on this discussion}
    Last edited by mestevet; 12-09-2011 at 05:06 PM.

  5. #5
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    What I heard long ago was when there is an ammeter or load meter (lot of early locos didn't have them, many L/subway and interurban "motors" had only an air pressure gauge for the brakes, not even a speedometer, they estimated speed by counting stuff like telephone poles per minute) it's usually connected to the second traction motor in the first truck (bogey) and reads only that one. So if that traction motor is out of service you're back to seat of the pants operation with no ammeter. For multiple units same would apply, ammeter reads only one traction motor, but since all the traction motors are being controlled simultaneously they would all have about the same average current. Unpowered cab car, hard to say, probably depends on the era but the one C&NW bilevel push-pull cabcar I saw in the early 70s had an ammeter along with gauges to read the engine temp and oil pressure remotely.

  6. #6

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    European practice at least, seems to be that the cabcar's cab is made to be as similar as possible to the cab of the locomotive/MU it is intended to operate with most commonly (many European railways have highly standardised cab designs, so that cab interiors would be pretty much identical anyway in various locomotive/MU types).

  7. #7
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    Dear collegues,

    sorry for jumping into an ageing thread, but I just had one or two thoughts when reading it...

    > if there is more than one powered loco in the consist, would it display the sum of the current for all locos, or perhaps the average current?

    1) First and foremost: That question wouldn't only apply to the cabcar, but to any consist with more than one motor in MU - after all, the leading powered motor will show you the amperage of the piece of iron under your seat, but not of the trailing helper behind you either. So regardless of what kind of equipment you're sitting in, as soon as you have more than one powered unit, you want to know how to find out what amperage this unit draws.

    2) Now I've some European point of view, based on my local experience in the Swiss Railroad scene, with a number of good friends working in railroad related jobs, and a cousin of my wife driving electric trains over the 7% DC Bernina Pass route. The following is what I've heard / learned from various friends and realtives working for the railroads:

    2a) In older times, or with older equipment used in MU, amperemeters only showed the values of the unit in which you were. When running a train with double header, an experienced motorman would therefore not even watch the amperemeter, but keep his eyes glued to the voltmeter, since U = R*I and therefore any change in amperage drawn by the train as a whole would immediately also reflect in voltage fluctuations. Thus by watching the drops in line voltage, the expericed engineer would judge whether his train was within limits or drawing too much juice. Hard to mimick in the sim I guess.

    2b) If one of our electric locomotives has e.g. four motors providing the power, then its cab will feature up to four Ammeters - ideally one for each motor (older equipment might just have one ammeter for two motors grouped in the same truck), since you must be able to quickly detect any malfunction or overload on any one of the motor before it burns through! And, in case of a problem, you need to know with certainty which traction motor or truck to shut off, since you absolutely need all the remaining power to rescue your train into the next siding...

    2c) In more modern times, i.e. speaking of the 1950s/60s onwards, some poles of the coaxial UiC cables - this is internationally standardized equipment - used to MU locomotives would be used to carry signals and indications between different pieces of equipment, along with all the other electric signals that need to travel back and fourth between the carriages of a train (status of passenger doors, stop request signalled by a passenger, onboard telephone between crew members, PA announcements to the passengers, etc, etc.).

    In its initial form, and provided the leading unit could translate the signals properly, trailing units would send an "overload" signal to the leading cab which would light a warning light as soon as a trailing unit was exceeding its limits on current drawn. It would however not inidcate which motor of the trailing unit was overloading, nor would it display the amount of the overload. Still, you had a chance to react and notch back before things started to smell funny in your back...

    The same UiC cable is used to connect cabcars and powered motor units, and therefore it has become general practice with many railroads over here to fit said cable permanently into most passenger carriages and even some freight cars (express mail and such) if there is a chance it will end up in a passenger consist. Of course, all cars of a train must carry the cable to allow for transmitting signals from one end to the other.

    2d) Nowadays, various types of such UiC cables exist, with varying numbers of poles or ports spliced into the cable. That increasing number of poles carried in a cable can be explained with additional needs, e.g. on board passenger information displays requiring additional nodes for transmitting the data through the train, activation of tilt systems in curves, monitoring of onboard security via CCTV and so on. However, since the whole specification is being monitored and governed by the UIC, the signals required to transmit signals between cabs are sitting on the same poles with all types of cables, from what I've learned. Thus you can also insert middle carriages with more complex cables into an consist with older motors and cabcars, and the controlls in the cabs either end will work, while the onboard info screen and the CCTV in the carriage in the middle has to stay dark since the respective pole is not supported/fed by the motor / cabcar. Not that this would be permanent practice or desired, but once in a while, you're just happy you can get all the basic functions of your lash-up working this way...

    2e) Modern equipment is fitted with more sophisitcated onboard electronics. If a trailing unit now develops a problem with any of its motors, it will use one of the poles of the coax cable to the leading unit to transmit a detailed error report, including e.g. the amount of overload and the motor in which it was registered. That sounds good, but unfortunately, more often than you'd think, error reports are false alarms - I see it way too often that after switching cabs from the motor to the cab car, an engineer is faced with the situation that a error report will prevent him/her from setting up the motor for the return trip (it hardly ever happens the other way round, when switching from the cab car to the motor). Usually, a walk back to the trailing motor and a manual reset in its cab resolves the problem so that it can go into push mode, but by then your train usually is already some 10 minutes past its scheduled departure time (scheduled turn-around times in my home turf for a 14-car Intercity train: typically 7-8 minutes!)... Concerning reliability of dara transmission, a rule of thumb locally circulated among engineers in Switzerland says: Up to four cabs in a consist is OK, more is calling for trouble...

    3) Final comment: The whole topic of MUing units and transmitting all kinds of signals through a train is a highly technical subject, filling many many binders in the tech libraries of a railroad. I am sure I have simplified things to an alarming amount here, and maybe I even summed up the explanations offered to me by engineers a bit inaccuratly when it comes to details. But I hope I offered some more or less accurate food for thought concerning the essentials behind it...

    Cheers, Lukas
    Last edited by Swissie; 09-01-2012 at 09:49 AM. Reason: clarity, typo, details
    Lukas a.k.a. Swissie

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