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.
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.
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.
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
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?
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.
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.
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?
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:
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.
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.
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.
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.
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.)
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?
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.
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.
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
On Friday, 11 January 2019 06:34:07 UTC+1, David Lesher wrote:DC motors. The use of induction motors in railway traction didn't become viable until the 1980s, a full century after Tesla invented them.
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 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.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.
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
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 DCmotors 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 ormultiple 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.
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.
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.
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.
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.
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.
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.
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.
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
First time I have an explanation for 25 Hz power that made sense.
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.
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.
On 1/11/2019 04:58, rcp27g@gmail.com wrote:
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.
First time I have an explanation for 25 Hz power that made sense.
Robin
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 wouldhave 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
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.
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