• grounding, was: What is a trolleybus?

    From danny burstein@21:1/5 to David Lesher on Wed Jan 9 03:41:30 2019
    In <q13lao$6pe$2@reader2.panix.com> David Lesher <wb8foz@panix.com> writes:

    hancock4@bbs.cpcn.com writes:

    Rails aren't grounded through the roadbed?

    No. They are isolated from ground; the return currents go via
    those cables Danny mentioned through a Wee_Z bond low pass
    filter to the substation. That's so the signaling system will
    work.

    Huh? I'll agree that a hefty chunk of the current goes back
    to, well, somewhere... but it would be damn tricky to isolate
    metal tracks from ground.

    There are a gazillion metal plates and spikes fastning
    the track to, well, the ground. Even if they've got
    rubber padding (which sure ain't universal) there's plenty
    of metal to metal to ground connectivity.

    --
    _____________________________________________________
    Knowledge may be power, but communications is the key
    dannyb@panix.com
    [to foil spammers, my address has been double rot-13 encoded]

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From spsfman@21:1/5 to danny burstein on Tue Jan 8 22:09:10 2019
    On 1/8/2019 7:41 PM, danny burstein wrote:
    In <q13lao$6pe$2@reader2.panix.com> David Lesher <wb8foz@panix.com> writes:

    hancock4@bbs.cpcn.com writes:

    Rails aren't grounded through the roadbed?

    No. They are isolated from ground; the return currents go via
    those cables Danny mentioned through a Wee_Z bond low pass
    filter to the substation. That's so the signaling system will
    work.

    Huh? I'll agree that a hefty chunk of the current goes back
    to, well, somewhere... but it would be damn tricky to isolate
    metal tracks from ground.

    There are a gazillion metal plates and spikes fastning
    the track to, well, the ground. Even if they've got
    rubber padding (which sure ain't universal) there's plenty
    of metal to metal to ground connectivity.


    Perhaps my understanding is way off, but, with DC, doesn't the ground
    have to return to the source rather than just to the actual earth,
    doesn't it?

    It was my simple understanding that with AC that wasn't necessary but
    with DC it was. That was one of the reasons AC won out over DC for
    domestic electricity. Didn't Edison have a complex set of heavy return
    (ground) wiring to maintain in lower Manhattan, and wasn't that part of
    what killed DC.

    I'd love to have non-insulting comments. If I'm wrong, tell me,
    politely. If I'm somewhat right, an affirmation would be nice.

    Cheers,

    DAVe

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  • From John Levine@21:1/5 to wb8foz@panix.com on Wed Jan 9 14:38:58 2019
    In article <q13lao$6pe$2@reader2.panix.com>,
    David Lesher <wb8foz@panix.com> wrote:
    hancock4@bbs.cpcn.com writes:


    Rails aren't grounded through the roadbed?

    No. They are isolated from ground; the return currents go via
    those cables Danny mentioned through a Wee_Z bond low pass
    filter to the substation. That's so the signaling system will
    work.

    This sounds peculiar to 600 or 750V DC third rail systems. 12 or 25Kv
    AC systems with catenary doubtles have different issues and much lower
    current.

    --
    Regards,
    John Levine, johnl@iecc.com, Primary Perpetrator of "The Internet for Dummies", Please consider the environment before reading this e-mail. https://jl.ly

    --- SoupGate-Win32 v1.05
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  • From Larry Sheldon@21:1/5 to spsfman on Wed Jan 9 10:38:57 2019
    On 1/9/2019 00:09, spsfman wrote:
    On 1/8/2019 7:41 PM, danny burstein wrote:
    In <q13lao$6pe$2@reader2.panix.com> David Lesher <wb8foz@panix.com>
    writes:

    hancock4@bbs.cpcn.com writes:

    Rails aren't grounded through the roadbed?

    No. They are isolated from ground; the return currents go via
    those cables Danny mentioned through a Wee_Z bond low pass
    filter to the substation. That's so the signaling system will
    work.

    Huh?  I'll agree that a hefty chunk of the current goes back
    to, well, somewhere...  but it would be damn tricky to isolate
    metal tracks from ground.

    There are a gazillion metal plates and spikes fastning
    the track to, well, the ground.  Even if they've got
    rubber padding (which sure ain't universal) there's plenty
    of metal to metal to ground connectivity.


    Perhaps my understanding is way off, but, with DC, doesn't the ground
    have to return to the source rather than just to the actual earth,
    doesn't it?

    It was my simple understanding that with AC that wasn't necessary but
    with DC it was. That was one of the reasons AC won out over DC for
    domestic electricity. Didn't Edison have a complex set of heavy return (ground) wiring to maintain in lower Manhattan, and wasn't that part of
    what killed DC.

    I'd love to have non-insulting comments. If I'm wrong, tell me,
    politely. If I'm somewhat right, an affirmation would be nice.

    Cheers,

    DAVe

    I am not sure how railroads and elevators and such do it now but I
    suspect there are as many standards as there are governing boards.

    But there are some things I am pretty sure of.

    One is that builders of transmission facilities HATE buying copper so if
    there is no reason not to, one of the conductors in the system will be
    Earth, AC, DC, or RF.

    When I was a little kid, people who lived on streets with street cars
    had (I think I remember) corrosion problems with buried metal stiff like
    water pipes. (What I am sure I remember is later we had a house on a
    street where every house wit a streetlamp near the water meter had to
    replace the water pipe every ten years or make extraordinary repairs.)

    We did not have any electric trains and the signal systems were base on Wheatstone bridges which were balanced (I think) for the "no train
    present" condition on the rails which were bonded longitudinally but not
    (as far as I could tell) isolated from ground except by the
    creosote-soaked sleepers. Some signals and controls were activated by engine-whistle-microphone links.

    AS regards the original trolley bus connection lethality question, I
    still don't know the answer but I think if it were mine to solve I would provide and on-board battery to provide for lights, controls and such, recharged but trolley power when available. I would have the
    high-voltage part of the system isolated from the bus body, and probably arrange for the poles to be disconnected from the wires electrically if
    the doors are open.

    Does the presence of poles imply DC service? Why?
    --
    quis custodiet ipsos custodes?
    -- Juvenal

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  • From Robert Heller@21:1/5 to lfsheldon@gmail.com on Wed Jan 9 11:58:38 2019
    At Wed, 9 Jan 2019 10:38:57 -0600 Larry Sheldon <lfsheldon@gmail.com> wrote:


    On 1/9/2019 00:09, spsfman wrote:
    On 1/8/2019 7:41 PM, danny burstein wrote:
    In <q13lao$6pe$2@reader2.panix.com> David Lesher <wb8foz@panix.com>
    writes:

    hancock4@bbs.cpcn.com writes:

    Rails aren't grounded through the roadbed?

    No. They are isolated from ground; the return currents go via
    those cables Danny mentioned through a Wee_Z bond low pass
    filter to the substation. That's so the signaling system will
    work.

    Huh?  I'll agree that a hefty chunk of the current goes back
    to, well, somewhere...  but it would be damn tricky to isolate
    metal tracks from ground.

    There are a gazillion metal plates and spikes fastning
    the track to, well, the ground.  Even if they've got
    rubber padding (which sure ain't universal) there's plenty
    of metal to metal to ground connectivity.


    Perhaps my understanding is way off, but, with DC, doesn't the ground
    have to return to the source rather than just to the actual earth,
    doesn't it?

    It was my simple understanding that with AC that wasn't necessary but
    with DC it was. That was one of the reasons AC won out over DC for
    domestic electricity. Didn't Edison have a complex set of heavy return (ground) wiring to maintain in lower Manhattan, and wasn't that part of what killed DC.

    I'd love to have non-insulting comments. If I'm wrong, tell me,
    politely. If I'm somewhat right, an affirmation would be nice.

    Cheers,

    DAVe

    I am not sure how railroads and elevators and such do it now but I
    suspect there are as many standards as there are governing boards.

    But there are some things I am pretty sure of.

    One is that builders of transmission facilities HATE buying copper so if there is no reason not to, one of the conductors in the system will be
    Earth, AC, DC, or RF.

    When I was a little kid, people who lived on streets with street cars
    had (I think I remember) corrosion problems with buried metal stiff like water pipes. (What I am sure I remember is later we had a house on a
    street where every house wit a streetlamp near the water meter had to
    replace the water pipe every ten years or make extraordinary repairs.)

    We did not have any electric trains and the signal systems were base on Wheatstone bridges which were balanced (I think) for the "no train
    present" condition on the rails which were bonded longitudinally but not
    (as far as I could tell) isolated from ground except by the
    creosote-soaked sleepers. Some signals and controls were activated by engine-whistle-microphone links.

    AS regards the original trolley bus connection lethality question, I
    still don't know the answer but I think if it were mine to solve I would provide and on-board battery to provide for lights, controls and such, recharged but trolley power when available. I would have the
    high-voltage part of the system isolated from the bus body, and probably arrange for the poles to be disconnected from the wires electrically if
    the doors are open.

    Does the presence of poles imply DC service? Why?

    Tradition. The *early* subways and trolley systems were 600VDC (or so). At the time AC was not on the radar (more or less). The "modern" LRVs (like the
    Boeing ones in Boston) use pantographs, not trolley poles like the old PCC cars, but use the same wires at the same 600VDC.

    Generally the AC is a much higher voltage, which needs bigger insulators and more air separation overhead (higher trolley wires), and is pretty much not suitable for ground-based power (eg third rail).

    --
    Robert Heller -- 978-544-6933
    Deepwoods Software -- Custom Software Services
    http://www.deepsoft.com/ -- Linux Administration Services
    heller@deepsoft.com -- Webhosting Services

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    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From hounslow3@yahoo.co.uk@21:1/5 to spsfman on Wed Jan 9 18:50:21 2019
    On 09/01/2019 06:09, spsfman wrote:
    On 1/8/2019 7:41 PM, danny burstein wrote:
    In <q13lao$6pe$2@reader2.panix.com> David Lesher <wb8foz@panix.com>
    writes:

    hancock4@bbs.cpcn.com writes:

    Rails aren't grounded through the roadbed?

    No. They are isolated from ground; the return currents go via
    those cables Danny mentioned through a Wee_Z bond low pass
    filter to the substation. That's so the signaling system will
    work.

    Huh?  I'll agree that a hefty chunk of the current goes back
    to, well, somewhere...  but it would be damn tricky to isolate
    metal tracks from ground.

    There are a gazillion metal plates and spikes fastning
    the track to, well, the ground.  Even if they've got
    rubber padding (which sure ain't universal) there's plenty
    of metal to metal to ground connectivity.


    Perhaps my understanding is way off, but, with DC, doesn't the ground
    have to return to the source rather than just to the actual earth,
    doesn't it?

    It was my simple understanding that with AC that wasn't necessary but
    with DC it was. That was one of the reasons AC won out over DC for
    domestic electricity. Didn't Edison have a complex set of heavy return (ground) wiring to maintain in lower Manhattan, and wasn't that part of
    what killed DC.

    I'd love to have non-insulting comments. If I'm wrong, tell me,
    politely. If I'm somewhat right, an affirmation would be nice.

    Don't worry, I like to think that we are all nice enough that we don't
    see the need to insult if somebody who is asking a question or trying to understand something is incorrect.

    I myself have learned much on these groups, and continue to do so. And
    that is because somebody has either corrected me if I was mistaken or
    explained something that I did not quite understand.

    So, ask away and learn. And maybe your questions will lead to other
    topics of discussion that you and others could find interesting.

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From hancock4@bbs.cpcn.com@21:1/5 to spsfman on Wed Jan 9 13:09:29 2019
    On Wednesday, January 9, 2019 at 1:09:39 AM UTC-5, spsfman wrote:
    On 1/8/2019 7:41 PM, danny burstein wrote:
    In <q13lao$6pe$2@reader2.panix.com> David Lesher <wb8foz@panix.com> writes:

    hancock4@bbs.cpcn.com writes:

    Rails aren't grounded through the roadbed?

    No. They are isolated from ground; the return currents go via
    those cables Danny mentioned through a Wee_Z bond low pass
    filter to the substation. That's so the signaling system will
    work.

    Huh? I'll agree that a hefty chunk of the current goes back
    to, well, somewhere... but it would be damn tricky to isolate
    metal tracks from ground.

    There are a gazillion metal plates and spikes fastning
    the track to, well, the ground. Even if they've got
    rubber padding (which sure ain't universal) there's plenty
    of metal to metal to ground connectivity.


    Perhaps my understanding is way off, but, with DC, doesn't the ground
    have to return to the source rather than just to the actual earth,
    doesn't it?

    It was my simple understanding that with AC that wasn't necessary but
    with DC it was. That was one of the reasons AC won out over DC for
    domestic electricity. Didn't Edison have a complex set of heavy return (ground) wiring to maintain in lower Manhattan, and wasn't that part of
    what killed DC.

    Originally, telegraph lines used a single conductor with ground
    as the return. That worked reasonably well. When they went to
    teleprinters and carrier, they needed better transmission
    and switched to metallic circuits.

    When the telephone came out, that too used a single conductor
    and ground return, but the transmission quality was very poor.
    So early on they switched to metallic circuits, too.

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From hancock4@bbs.cpcn.com@21:1/5 to Larry Sheldon on Wed Jan 9 13:15:27 2019
    On Wednesday, January 9, 2019 at 11:39:01 AM UTC-5, Larry Sheldon wrote:
    On 1/9/2019 00:09, spsfman wrote:
    On 1/8/2019 7:41 PM, danny burstein wrote:
    In <q13lao$6pe$2@reader2.panix.com> David Lesher <wb8foz@panix.com>
    writes:

    hancock4@bbs.cpcn.com writes:

    Rails aren't grounded through the roadbed?

    No. They are isolated from ground; the return currents go via
    those cables Danny mentioned through a Wee_Z bond low pass
    filter to the substation. That's so the signaling system will
    work.

    Huh?  I'll agree that a hefty chunk of the current goes back
    to, well, somewhere...  but it would be damn tricky to isolate
    metal tracks from ground.

    There are a gazillion metal plates and spikes fastning
    the track to, well, the ground.  Even if they've got
    rubber padding (which sure ain't universal) there's plenty
    of metal to metal to ground connectivity.


    Perhaps my understanding is way off, but, with DC, doesn't the ground
    have to return to the source rather than just to the actual earth,
    doesn't it?

    It was my simple understanding that with AC that wasn't necessary but
    with DC it was. That was one of the reasons AC won out over DC for domestic electricity. Didn't Edison have a complex set of heavy return (ground) wiring to maintain in lower Manhattan, and wasn't that part of what killed DC.

    I'd love to have non-insulting comments. If I'm wrong, tell me,
    politely. If I'm somewhat right, an affirmation would be nice.

    Cheers,

    DAVe

    I am not sure how railroads and elevators and such do it now but I
    suspect there are as many standards as there are governing boards.

    But there are some things I am pretty sure of.

    One is that builders of transmission facilities HATE buying copper so if there is no reason not to, one of the conductors in the system will be Earth, AC, DC, or RF.

    Unfortunately, using the ground as a return is a poor medium,
    so communication and power companies long ago realized it was
    necessary to use copper.



    When I was a little kid, people who lived on streets with street cars
    had (I think I remember) corrosion problems with buried metal stiff like water pipes. (What I am sure I remember is later we had a house on a
    street where every house wit a streetlamp near the water meter had to replace the water pipe every ten years or make extraordinary repairs.)

    Our trolley company had detector vehicles that looked for leaks, so
    as to avoid corrosion of nearby pipes.


    We did not have any electric trains and the signal systems were base on Wheatstone bridges which were balanced (I think) for the "no train
    present" condition on the rails which were bonded longitudinally but not
    (as far as I could tell) isolated from ground except by the
    creosote-soaked sleepers. Some signals and controls were activated by engine-whistle-microphone links.

    I never heard of an "engine whistle microphone" link. Until relatively recently, microphone and detector technology was not good enough to
    accurately discern real from false signals. Signals had to be highly
    reliable.


    AS regards the original trolley bus connection lethality question, I
    still don't know the answer but I think if it were mine to solve I would provide and on-board battery to provide for lights, controls and such, recharged but trolley power when available. I would have the
    high-voltage part of the system isolated from the bus body, and probably arrange for the poles to be disconnected from the wires electrically if
    the doors are open.

    For nearly 100 years electric vehicles had a battery to supply
    power for controls and emergency lights, but not traction.



    Does the presence of poles imply DC service? Why?

    I think poles could be used for either AC or DC service. I
    think the decision to use poles or pantographs depends on the
    type of service. Pantographs are better for higher speeds
    and reversing ends. Note that SEPTA's city streetcars still
    use poles, while its suburban cars use pantographs.

    I think trackless trolleys will use poles due to the double feed.

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From Larry Sheldon@21:1/5 to hancock4@bbs.cpcn.com on Wed Jan 9 21:11:58 2019
    On 1/9/2019 15:15, hancock4@bbs.cpcn.com wrote:
    On Wednesday, January 9, 2019 at 11:39:01 AM UTC-5, Larry Sheldon wrote:
    On 1/9/2019 00:09, spsfman wrote:
    On 1/8/2019 7:41 PM, danny burstein wrote:
    In <q13lao$6pe$2@reader2.panix.com> David Lesher <wb8foz@panix.com>
    writes:

    hancock4@bbs.cpcn.com writes:

    <gobble on>
    <gobble off>
    We did not have any electric trains and the signal systems were base on
    Wheatstone bridges which were balanced (I think) for the "no train
    present" condition on the rails which were bonded longitudinally but not
    (as far as I could tell) isolated from ground except by the
    creosote-soaked sleepers. Some signals and controls were activated by
    engine-whistle-microphone links.

    I never heard of an "engine whistle microphone" link. Until relatively recently, microphone and detector technology was not good enough to accurately discern real from false signals. Signals had to be highly reliable.

    I am pretty sure I have over my 80 summers seen several examples but one
    I remember with clarity was at Southern Pacific's station on their
    Peninsula
    line. Eastbound trains stopped at the station just west of the
    Sunnyvale Avenue crossing and the crossing guards would time out and
    rise, clearing the crossing. There was a microphone on a box on a pole
    that allowed the train to whistle the arms back down. (I don't know if
    the lash-up had enough intelligence to listen for long long short long
    or just loud. I AM pretty sure that the spare engine that parked on a
    siding there could whistle down the arms.


    --
    quis custodiet ipsos custodes?
    -- Juvenal

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From Larry Sheldon@21:1/5 to Larry Sheldon on Wed Jan 9 21:16:48 2019
    On 1/9/2019 21:11, Larry Sheldon wrote:
    On 1/9/2019 15:15, hancock4@bbs.cpcn.com wrote:
    On Wednesday, January 9, 2019 at 11:39:01 AM UTC-5, Larry Sheldon wrote:
    On 1/9/2019 00:09, spsfman wrote:
    On 1/8/2019 7:41 PM, danny burstein wrote:
    In <q13lao$6pe$2@reader2.panix.com> David Lesher <wb8foz@panix.com>
    writes:

    hancock4@bbs.cpcn.com writes:

    <gobble on>
    <gobble off>
    We did not have any electric trains and the signal systems were base on
    Wheatstone bridges which were balanced (I think) for the "no train
    present" condition on the rails which were bonded longitudinally but not >>> (as far as I could tell) isolated from ground except by the
    creosote-soaked sleepers.  Some signals and controls were activated by
    engine-whistle-microphone links.

    I never heard of an "engine whistle microphone" link.  Until relatively
    recently, microphone and detector technology was not good enough to
    accurately discern real from false signals.  Signals had to be highly
    reliable.

    I am pretty sure I have over my 80 summers seen several examples but one
    I remember with clarity was at Southern Pacific's station on their
    Peninsula
    line.  Eastbound trains stopped at the station just west of the
    Sunnyvale Avenue crossing and the crossing guards would time out and
    rise, clearing the crossing.  There was a microphone on a box on a pole
    that allowed the train to whistle the arms back down.  (I don't know if
    the lash-up had enough intelligence to listen for long long short long
    or just loud.  I AM pretty sure that the spare engine that parked on a siding there could whistle down the arms.

    There are loads of places where they same thing is accomplished by tracks circuits closer to the street. I don't know one way is chosen over the other--the thing probably dates back to steam if that makes a difference.


    --
    quis custodiet ipsos custodes?
    -- Juvenal

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From Robert Heller@21:1/5 to hancock4@bbs.cpcn.com on Wed Jan 9 21:19:57 2019
    At Wed, 9 Jan 2019 13:09:29 -0800 (PST) hancock4@bbs.cpcn.com wrote:


    On Wednesday, January 9, 2019 at 1:09:39 AM UTC-5, spsfman wrote:
    On 1/8/2019 7:41 PM, danny burstein wrote:
    In <q13lao$6pe$2@reader2.panix.com> David Lesher <wb8foz@panix.com> writes:

    hancock4@bbs.cpcn.com writes:

    Rails aren't grounded through the roadbed?

    No. They are isolated from ground; the return currents go via
    those cables Danny mentioned through a Wee_Z bond low pass
    filter to the substation. That's so the signaling system will
    work.

    Huh? I'll agree that a hefty chunk of the current goes back
    to, well, somewhere... but it would be damn tricky to isolate
    metal tracks from ground.

    There are a gazillion metal plates and spikes fastning
    the track to, well, the ground. Even if they've got
    rubber padding (which sure ain't universal) there's plenty
    of metal to metal to ground connectivity.


    Perhaps my understanding is way off, but, with DC, doesn't the ground
    have to return to the source rather than just to the actual earth,
    doesn't it?

    It was my simple understanding that with AC that wasn't necessary but
    with DC it was. That was one of the reasons AC won out over DC for
    domestic electricity. Didn't Edison have a complex set of heavy return (ground) wiring to maintain in lower Manhattan, and wasn't that part of what killed DC.

    Originally, telegraph lines used a single conductor with ground
    as the return. That worked reasonably well. When they went to
    teleprinters and carrier, they needed better transmission
    and switched to metallic circuits.

    When the telephone came out, that too used a single conductor
    and ground return, but the transmission quality was very poor.
    So early on they switched to metallic circuits, too.

    What is going on here is with twisted pair and/or "balanced" circuits is
    noise cancelation and improving signal-to-noise ratios. This is a different problem from bulk power transmission.






    --
    Robert Heller -- 978-544-6933
    Deepwoods Software -- Custom Software Services
    http://www.deepsoft.com/ -- Linux Administration Services
    heller@deepsoft.com -- Webhosting Services

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From Larry Sheldon@21:1/5 to Robert Heller on Thu Jan 10 00:06:02 2019
    On 1/9/2019 21:19, Robert Heller wrote:
    At Wed, 9 Jan 2019 13:09:29 -0800 (PST) hancock4@bbs.cpcn.com wrote:


    On Wednesday, January 9, 2019 at 1:09:39 AM UTC-5, spsfman wrote:
    On 1/8/2019 7:41 PM, danny burstein wrote:
    In <q13lao$6pe$2@reader2.panix.com> David Lesher <wb8foz@panix.com> writes:
    hancock4@bbs.cpcn.com writes:

    When the telephone came out, that too used a single conductor
    and ground return, but the transmission quality was very poor.
    So early on they switched to metallic circuits, too.

    What is going on here is with twisted pair and/or "balanced" circuits is noise cancellation and improving signal-to-noise ratios. This is a different problem from bulk power transmission.

    Tru Dat. But even in power, in my limited experience, to the extent
    possible
    stuff is arranged so most of the power travels via well balanced,
    Y-connected three phase circuits with the common-point of the three transformers grounded very little current flowing in the ground.

    --
    quis custodiet ipsos custodes?
    -- Juvenal

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From rcp27g@gmail.com@21:1/5 to Larry Sheldon on Thu Jan 10 02:28:06 2019
    On Wednesday, 9 January 2019 17:39:01 UTC+1, Larry Sheldon wrote:

    I am not sure how railroads and elevators and such do it now but I
    suspect there are as many standards as there are governing boards.

    But there are some things I am pretty sure of.

    One is that builders of transmission facilities HATE buying copper so if there is no reason not to, one of the conductors in the system will be Earth, AC, DC, or RF.

    When I was a little kid, people who lived on streets with street cars
    had (I think I remember) corrosion problems with buried metal stiff like water pipes. (What I am sure I remember is later we had a house on a
    street where every house wit a streetlamp near the water meter had to replace the water pipe every ten years or make extraordinary repairs.)

    For very low current applications like telephone you can just about get away with it, but for something like railway traction, the current involved is sufficiently high that the electrolytic corrosion from earth-return is extremely damaging. Modern on-
    street tramways have quite strict rules about how much earth leakage current is permissible. This kind of electrolytic corrosion is much less of a problem with AC systems.

    AS regards the original trolley bus connection lethality question, I
    still don't know the answer but I think if it were mine to solve I would provide and on-board battery to provide for lights, controls and such, recharged but trolley power when available. I would have the
    high-voltage part of the system isolated from the bus body, and probably arrange for the poles to be disconnected from the wires electrically if
    the doors are open.

    That all seems like a pretty sensible design concept. Add in some attempt to make as good an earth connection to the road surface too.

    Does the presence of poles imply DC service? Why?

    Not necessarily. Pretty much all on-street systems are DC, though (with a few exceptions, for example the Chur-Arosa line in Switzerland running through the streets of Chur). DC is much easier to handle on board in terms of controlling the power. The
    reason not to use DC is to allow a much higher OHL voltage, which allows the feeders and substations to be significantly further apart. Most mainline railways have converged on 25 kV as the right balance of safety and economics, but plenty of legacy
    systems remain. For on-street running, though, anything more than 1 kV is going to have serious safety implications, which is why most systems both streetcar and trolleybus run somewhere in the 500 - 750 V region. At that voltage there is really no
    advantage to using AC, but using AC adds complexity to the vehicle. Hence DC is favoured.

    Trolley poles have almost entirely been replaced by pantographs for single-wire rail (with track return) applications for a whole host of reasons: better high speed performance, not directionally sensitive, much easier to make junctions in the OHL. The
    trolley pole has one specific advantage, though, and that is that it does not require the vehicle to be aligned directly under the overhead. For a rail based vehicle this is a non-issue as the track defines the path of the vehicle, but for a trolley bus,
    the flexibility of vehicle path is inherent to the system, hence trolley poles remain in use.

    As a side note, there are dual-overhead pantograph base systems, eg the three-phase AC overhead on the Jungfraubahn in Switzerland, but they are decidedly niche.

    Robin

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  • From David Lesher@21:1/5 to spsfman on Fri Jan 11 05:34:07 2019
    spsfman <spsffan@hotmail.com> writes:

    Huh? I'll agree that a hefty chunk of the current goes back
    to, well, somewhere... but it would be damn tricky to isolate
    metal tracks from ground.

    Railroads have been managing for a long time.


    Perhaps my understanding is way off, but, with DC, doesn't the ground
    have to return to the source rather than just to the actual earth,
    doesn't it?

    It was my simple understanding that with AC that wasn't necessary but
    with DC it was. That was one of the reasons AC won out over DC for
    domestic electricity. Didn't Edison have a complex set of heavy return >(ground) wiring to maintain in lower Manhattan, and wasn't that part of
    what killed DC.

    I'd love to have non-insulting comments. If I'm wrong, tell me,
    politely. If I'm somewhat right, an affirmation would be nice.

    In the early days, AC & DC each held aces.

    For DC, it was we knew how to make DC motors that worked. They
    were heavy and large, but delivered great torque at 0 RPM, vital
    for starting a train or trolley (or a V8..). But DC is usable
    at low voltages (if you understand that 60V is "low". And for a
    given power, say 10 KW (~13 HP) the lower the voltage the higher
    the current;

    10KW = 600v*16.8A = 60V*168A = 6000V*1.6A etc.

    and the higher the current, the larger the cables needed for the same loss.

    For AC, we didn't know how to make AC motors. But AC allows us
    to use a transformer. A transformer lets us change the voltage
    up or down easily. (Yes, there are transformer losses I'm
    skipping...)

    There's no free lunch; the power is the same in & out, but we
    can feed the transformer at 6000V and get 60V out. When we pull
    150A at 60V (9KW) we'll need 9000/6000 or 1.5A at 6KV. With 1.5A
    we need smaller cable, less copper, and still enjoy only a small
    loss.

    Enter an under-sung genius, Nikola Tesla. He made the first
    viable AC motors. Game Over. With transformers, you could put in
    HV lines to near the load, step down the voltage and go.

    Tesla's motors were fixed speed; set by the line frequency (60
    Hz here, 50 Hz in the UK and less-rebelling colonies Belize,
    Falklands, etc.) DC motors were variable speed. You needed that
    for transit and rail and elevators and .....

    There's also a limit to the voltage you can use; will it arc
    through the air to ground or supports? [In both AC & DC
    systems one side is grounded for safety reasons.] Transit has
    traditionally used 600-750VDC, but BART went to 1000V, and
    regretted it later.

    The NE Corridor was electrified in ~1905. The catenary is
    at 12KV AC. The Acela engines draw ~4E9 watts each, and the
    HVAC is ~10MW, I read somewhere. But overhead, there's 132 KV
    transmission lines overhead, with transformers every 8 miles or
    so apart.

    The irony is this: since AC motors are stuck at line frequency
    speed, locomotives used DC motors; even those getting AC from
    the NEC cat system. How takes too long for this post, but...

    And further, we now have a way to use Tesla's electric motors
    directly, and we do so.

    Do read:

    Empires of Light: Edison, Tesla, Westinghouse, and the Race to Electrify the World

    for insight...

    --
    A host is a host from coast to coast.................wb8foz@nrk.com
    & no one will talk to a host that's close..........................
    Unless the host (that isn't close).........................pob 1433
    is busy, hung or dead....................................20915-1433

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From rcp27g@gmail.com@21:1/5 to David Lesher on Fri Jan 11 02:58:28 2019
    On Friday, 11 January 2019 06:34:07 UTC+1, David Lesher wrote:
    spsfman <spsffan@hotmail.com> writes:

    Perhaps my understanding is way off, but, with DC, doesn't the ground
    have to return to the source rather than just to the actual earth,
    doesn't it?

    It was my simple understanding that with AC that wasn't necessary but
    with DC it was. That was one of the reasons AC won out over DC for >domestic electricity. Didn't Edison have a complex set of heavy return >(ground) wiring to maintain in lower Manhattan, and wasn't that part of >what killed DC.

    I'd love to have non-insulting comments. If I'm wrong, tell me,
    politely. If I'm somewhat right, an affirmation would be nice.

    In the early days, AC & DC each held aces.

    For DC, it was we knew how to make DC motors that worked.

    For AC, we didn't know how to make AC motors.

    Enter an under-sung genius, Nikola Tesla. He made the first
    viable AC motors. Game Over.

    Tesla's motors were fixed speed; set by the line frequency

    Sorry for the copious snippage. I think you're rather mixing up the timeline.

    Tesla invented the AC induction motor in the 1880s. DC railway electrification became a practical proposition in the 1880s. Early (low frequency) AC followed about 20 years later, but mains frequency wasn't viable until the 1960s. All of these used DC
    motors. The use of induction motors in railway traction didn't become viable until the 1980s, a full century after Tesla invented them.

    DC motors have their output controlled by voltage. AC motors have their output determined by the voltage to an extent and by the difference between the rotational speed and the supply frequency, in an annoyingly non-linear fashion.

    Early DC motors had a mix of resistances and series/parallel switching for control. Early AC wired the field coils in series with the armature on a DC motor and treated the AC as "psuedo" DC. This doesn't work at mains frequency because of inductance
    effects, but at lower frequency you can get away with it. This is why the orginal PRR system went with 25 Hz and the De/At/CH system uses 16.7 Hz. Control can be acheived using tap changers.

    In the 1960s rectifiers with the power needed for a locomotive and the robustness to survive a railway locomotive environment became small and light enough to fit on one. At that point mains frequency AC became viable, again using tap changers and DC
    motors for control. In the 1970s power electronics scaled up to the needed power requirements and clever things like choppers and thyristors replaced resistances or tap changers.

    In the 1980s power electronics and microprocessor control developed to the point where a DC supply could be converted to a 3 phase AC supply where both the voltage and frequency can be readily controlled, in a package that can fit on a locomotive or
    multiple unit. It was this key advance that allowed AC motors to replace DC motors. This is now standard.

    Incidentally the same VVVF 3 phase supply is what is used on modern "AC" diesel electric locomotives. Because the output of the traction motor is closely related to the difference between the inverter frequency and the rotational speed of the motor, it
    allows really close control over the traction motors, allowing things like creep control (making the wheels rotate just a tiny bit faster than the road speed dictates) that gives good heavy haul performance.

    Robin

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From Larry Sheldon@21:1/5 to rcp27g@gmail.com on Fri Jan 11 14:29:20 2019
    On 1/11/2019 04:58, rcp27g@gmail.com wrote:
    On Friday, 11 January 2019 06:34:07 UTC+1, David Lesher wrote:
    spsfman <spsffan@hotmail.com> writes:

    Perhaps my understanding is way off, but, with DC, doesn't the ground
    have to return to the source rather than just to the actual earth,
    doesn't it?

    It was my simple understanding that with AC that wasn't necessary but
    with DC it was. That was one of the reasons AC won out over DC for
    domestic electricity. Didn't Edison have a complex set of heavy return
    (ground) wiring to maintain in lower Manhattan, and wasn't that part of
    what killed DC.

    I'd love to have non-insulting comments. If I'm wrong, tell me,
    politely. If I'm somewhat right, an affirmation would be nice.

    In the early days, AC & DC each held aces.

    For DC, it was we knew how to make DC motors that worked.

    For AC, we didn't know how to make AC motors.

    Enter an under-sung genius, Nikola Tesla. He made the first
    viable AC motors. Game Over.

    Tesla's motors were fixed speed; set by the line frequency

    Sorry for the copious snippage. I think you're rather mixing up the timeline.

    Tesla invented the AC induction motor in the 1880s. DC railway electrification became a practical proposition in the 1880s. Early (low frequency) AC followed about 20 years later, but mains frequency wasn't viable until the 1960s. All of these used
    DC motors. The use of induction motors in railway traction didn't become viable until the 1980s, a full century after Tesla invented them.

    DC motors have their output controlled by voltage. AC motors have their output determined by the voltage to an extent and by the difference between the rotational speed and the supply frequency, in an annoyingly non-linear fashion.

    Early DC motors had a mix of resistances and series/parallel switching for control. Early AC wired the field coils in series with the armature on a DC motor and treated the AC as "psuedo" DC. This doesn't work at mains frequency because of inductance
    effects, but at lower frequency you can get away with it. This is why the orginal PRR system went with 25 Hz and the De/At/CH system uses 16.7 Hz. Control can be acheived using tap changers.

    In the 1960s rectifiers with the power needed for a locomotive and the robustness to survive a railway locomotive environment became small and light enough to fit on one. At that point mains frequency AC became viable, again using tap changers and DC
    motors for control. In the 1970s power electronics scaled up to the needed power requirements and clever things like choppers and thyristors replaced resistances or tap changers.

    In the 1980s power electronics and microprocessor control developed to the point where a DC supply could be converted to a 3 phase AC supply where both the voltage and frequency can be readily controlled, in a package that can fit on a locomotive or
    multiple unit. It was this key advance that allowed AC motors to replace DC motors. This is now standard.

    Incidentally the same VVVF 3 phase supply is what is used on modern "AC" diesel electric locomotives. Because the output of the traction motor is closely related to the difference between the inverter frequency and the rotational speed of the motor,
    it allows really close control over the traction motors, allowing things like creep control (making the wheels rotate just a tiny bit faster than the road speed dictates) that gives good heavy haul performance.

    Robin

    First time I have an explanation for 25 Hz power that made sense.
    --
    quis custodiet ipsos custodes?
    -- Juvenal

    --- SoupGate-Win32 v1.05
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  • From hancock4@bbs.cpcn.com@21:1/5 to Larry Sheldon on Sat Jan 12 12:30:48 2019
    On Friday, January 11, 2019 at 3:29:23 PM UTC-5, Larry Sheldon wrote:

    First time I have an explanation for 25 Hz power that made sense.

    25Hz was popular about 100 years ago. I think the power companies
    supplied it. Then well-regulated 60 Hz became the standard, but
    for years, power companies had to keep supplying 25 Hz since
    many industrial users has 25 Hz motors. Also, some had to supply
    DC since older customers had DC motors.

    The former PRR NEC remains 25 Hz.

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From rcp27g@gmail.com@21:1/5 to hanc...@bbs.cpcn.com on Sat Jan 12 13:38:45 2019
    On Saturday, 12 January 2019 21:30:49 UTC+1, hanc...@bbs.cpcn.com wrote:
    On Friday, January 11, 2019 at 3:29:23 PM UTC-5, Larry Sheldon wrote:

    First time I have an explanation for 25 Hz power that made sense.

    25Hz was popular about 100 years ago. I think the power companies
    supplied it. Then well-regulated 60 Hz became the standard, but
    for years, power companies had to keep supplying 25 Hz since
    many industrial users has 25 Hz motors. Also, some had to supply
    DC since older customers had DC motors.

    The former PRR NEC remains 25 Hz.

    25 Hz was a common mains frequency in the first half of the C20th. When the modern power grids established themselves, the 60 Hz (or 50 Hz depending on region) became established. If the PRR system had no frequency issues, it is likely they would have
    converted simply for the sake of standardisation. The reason that they didn't was the rolling stock wasn't able at the time to accept higher frequency. Now, pretty much all of the "needs low frequency" rolling stock is retired, but considering the
    lifetime of things like the GG1 and similar vintage vehicles, by the time the need for low frequency was passed, the capital for railway investment was less available.

    Robin

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From rcp27g@gmail.com@21:1/5 to David Lesher on Sat Jan 12 13:44:15 2019
    On Saturday, 12 January 2019 22:21:08 UTC+1, David Lesher wrote:
    John Levine <johnl@taugh.com> writes:


    This sounds peculiar to 600 or 750V DC third rail systems. 12 or 25Kv
    AC systems with catenary doubtles have different issues and much lower >current.

    Err, lower current? An Acela trainset draws ?15-20 Megawatts I think.
    Even at 12.5 KV, that's a few Amperes.

    20 MW at 12.5 kV is 1.6 kA. At 750 V, 1.6 kA provides 1.2 MW, or about 1600 hp. For streetcars or trolleybuses that's plenty. For a metro train or commuter rail, that's not going to offer much. For modern railway applications, 12.5 kV is a bit low
    voltage these days.

    Robin

    PS for pedantry: the kilo prefix is always lower case and the V for volts is always upper case, so it's kV, not KV or Kv.

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From John Levine@21:1/5 to All on Sat Jan 12 21:41:53 2019
    This sounds peculiar to 600 or 750V DC third rail systems. 12 or 25Kv
    AC systems with catenary doubtles have different issues and much lower >>current.

    Err, lower current? An Acela trainset draws ?15-20 Megawatts I think.
    Even at 12.5 KV, that's a few Amperes.

    It's a lot lower than it would be on a (hypothetical in this case) third rail.

    In the UK there are suburban services that run 100mph with third rail,
    like the line from London Waterloo to Bournemouth and Poole. The
    sparks can be pretty impressive, and the cabling sure is.

    The original routing of the Eurostar from Paris to London also arrived
    at Waterloo with the last part of the high speed trip on third rail.
    It now goes to St Pancras under OHLE (do we call it that in ths US?)
    the whole way.

    --
    Regards,
    John Levine, johnl@iecc.com, Primary Perpetrator of "The Internet for Dummies", Please consider the environment before reading this e-mail. https://jl.ly

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From rcp27g@gmail.com@21:1/5 to John Levine on Sat Jan 12 13:51:34 2019
    On Saturday, 12 January 2019 22:41:53 UTC+1, John Levine wrote:
    This sounds peculiar to 600 or 750V DC third rail systems. 12 or 25Kv
    AC systems with catenary doubtles have different issues and much lower >>current.

    Err, lower current? An Acela trainset draws ?15-20 Megawatts I think.
    Even at 12.5 KV, that's a few Amperes.

    It's a lot lower than it would be on a (hypothetical in this case) third rail.

    In the UK there are suburban services that run 100mph with third rail,
    like the line from London Waterloo to Bournemouth and Poole. The
    sparks can be pretty impressive, and the cabling sure is.

    The original routing of the Eurostar from Paris to London also arrived
    at Waterloo with the last part of the high speed trip on third rail.
    It now goes to St Pancras under OHLE (do we call it that in ths US?)
    the whole way.

    Eurostars were significantly limited in power on the 3rd rail, as the supply could only offer something like a third of the power available on 25 kV. The only reason the UK southern 3rd rail system extends as far as it does is for historical reasons.
    Now that multi-system vehicles are easy to build and design, there is really no reason to perpetuate such a system other than the expense of changing it out for something newer (see, also, the 25 Hz PRR NEC system).

    Robin

    --- SoupGate-Win32 v1.05
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  • From David Lesher@21:1/5 to John Levine on Sat Jan 12 21:21:07 2019
    John Levine <johnl@taugh.com> writes:


    This sounds peculiar to 600 or 750V DC third rail systems. 12 or 25Kv
    AC systems with catenary doubtles have different issues and much lower >current.

    Err, lower current? An Acela trainset draws ?15-20 Megawatts I think.
    Even at 12.5 KV, that's a few Amperes.

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From David Lesher@21:1/5 to rcp27g@gmail.com on Sun Jan 13 03:43:29 2019
    rcp27g@gmail.com writes:


    Tesla's motors were fixed speed; set by the line frequency

    Sorry for the copious snippage. I think you're rather mixing up the timeli= >ne.

    Tesla invented the AC induction motor in the 1880s. DC railway electrifica= >tion became a practical proposition in the 1880s. Early (low frequency) AC=
    followed about 20 years later, but mains frequency wasn't viable until the= 1960s. All of these used DC motors. The use of induction motors in railw=
    ay traction didn't become viable until the 1980s, a full century after Tesl= >a invented them.

    No arguments there. Tesla's polyphase motor was not usable for
    rail use until the semiconductor industry gave up high-power
    devices usable for Variable Frequency Drives {VFD}. (Save
    one line somewhere I read of that had two phases+ground
    supplied....)

    Single-phase Induction motors were ill-suited in several ways for rail use.

    DC motors have their output controlled by voltage. AC motors have their ou= >tput determined by the voltage to an extent and by the difference between t= >he rotational speed and the supply frequency, in an annoyingly non-linear f= >ashion.

    I was avoiding getting into slip and such in answering spsfman.
    But the max torque at 0 rpm is surely a reason why series "DC" motors
    have stayed around.

    Early DC motors had a mix of resistances and series/parallel switching for = >control. Early AC wired the field coils in series with the armature on a D= >C motor and treated the AC as "psuedo" DC. This doesn't work at mains freq= >uency because of inductance effects, but at lower frequency you can get awa= >y with it. This is why the orginal PRR system went with 25 Hz and the De/A= >t/CH system uses 16.7 Hz. Control can be acheived using tap changers. = 20

    ls:
    First time I have an explanation for 25 Hz power that made sense.

    Yep, few people seem to grasp that lower X(l) was the reason for
    the lower frequency power.


    In the 1980s power electronics and microprocessor control developed to the = >point where a DC supply could be converted to a 3 phase AC supply where bot= >h the voltage and frequency can be readily controlled, in a package that ca= >n fit on a locomotive or multiple unit. It was this key advance that allow= >ed AC motors to replace DC motors. This is now standard.

    But not universal; I've read that for some reasons, many new Diesel-Electric locomotives are still using series DC motors.

    Incidentally the same VVVF 3 phase supply is what is used on modern "AC" di= >esel electric locomotives. Because the output of the traction motor is clo= >sely related to the difference between the inverter frequency and the rotat= >ional speed of the motor, it allows really close control over the traction = >motors, allowing things like creep control (making the wheels rotate just a=
    tiny bit faster than the road speed dictates) that gives good heavy haul p=
    erformance.

    Yep, which adds to my wondering why they are not used exclusively.
    0 RPM torque, perhaps?

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From spsfman@21:1/5 to Larry Sheldon on Sat Jan 12 23:45:48 2019
    On 1/11/2019 12:29 PM, Larry Sheldon wrote:
    On 1/11/2019 04:58, rcp27g@gmail.com wrote:

    snip

    Early DC motors had a mix of resistances and series/parallel switching
    for control.  Early AC wired the field coils in series with the
    armature on a DC motor and treated the AC as "psuedo" DC.  This
    doesn't work at mains frequency because of inductance effects, but at
    lower frequency you can get away with it.  This is why the orginal PRR
    system went with 25 Hz and the De/At/CH system uses 16.7 Hz.  Control
    can be acheived using tap changers.


    Robin

    First time I have an explanation for 25 Hz power that made sense.

    snip

    Larry. I'll second that. Thanks for the excellent, well written
    explanation Robin

    DAve

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  • From hancock4@bbs.cpcn.com@21:1/5 to rcp...@gmail.com on Mon Jan 14 12:42:45 2019
    On Saturday, January 12, 2019 at 4:38:46 PM UTC-5, rcp...@gmail.com wrote:

    25 Hz was a common mains frequency in the first half of the C20th. When the modern power grids established themselves, the 60 Hz (or 50 Hz depending on region) became established. If the PRR system had no frequency issues, it is likely they would
    have converted simply for the sake of standardisation. The reason that they didn't was the rolling stock wasn't able at the time to accept higher frequency. Now, pretty much all of the "needs low frequency" rolling stock is retired, but considering the
    lifetime of things like the GG1 and similar vintage vehicles, by the time the need for low frequency was passed, the capital for railway investment was less available.

    I don't think there is anything left that requires 25 Hz; I think
    now all equipment can take either 25 or 60 Hz. However, I think
    some equipment is still locked into voltage, that is, an 11KV
    can't run on 25kV. The newest stuff is more flexible.

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From David Lesher@21:1/5 to hancock4@bbs.cpcn.com on Tue Jan 15 15:26:28 2019
    hancock4@bbs.cpcn.com writes:


    I don't think there is anything left that requires 25 Hz; I think
    now all equipment can take either 25 or 60 Hz. However, I think
    some equipment is still locked into voltage, that is, an 11KV
    can't run on 25kV. The newest stuff is more flexible.

    From what I have read, everything is now dual voltage (12/25)
    and frequency independent. It must be to be usable
    both on the south of NYC and north to Boston trackage.

    --
    A host is a host from coast to coast.................wb8foz@nrk.com
    & no one will talk to a host that's close..........................
    Unless the host (that isn't close).........................pob 1433
    is busy, hung or dead....................................20915-1433

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)