Ground return used for early telegraph?

[NTW]

I have read that, in the early days of the telegraph, two wires were used, but Steinheil, of optics fame, discovered that the circuit could be completed by 'earth return', using the ground as return ...conductor?

That's my question. It's hard to believe that currents strong enough to operate the telegraph could be produced by low-voltage batteries, with the high presumable resistance of the earth...
In those telegraph systems, or in some single-wire, earth-return power supplies that exist in some countries, does the electricity really circulate through the ground? Or does the ground work as a 'capacitor', as I have seen mentioned somewhere? But, if it's a capacitor, then where are the plates...?

 

[jedishrfu]

This may answer your question

http://www.connected-earth.com/Learningresources/Howitworks/Telegraph/Howthetelegraphworks/index.htm

 

[NTW]

Thanks, but -in that web page- I can't find any mention to ground return...

 

[zoki85]

In those telegraph systems, or in some single-wire, earth-return power supplies that exist in some countries, does the electricity really circulate through the ground? Or does the ground work as a 'capacitor', as I have seen mentioned somewhere? But, if it's a capacitor, then where are the plates...?

Currents really circulate through the ground

 

[NTW]

Currents really circulate through the ground

Well, I don't doubt that, in principle, but in the early telegraphs, where ground return was standard, the distances covered by the lines where often very large, and the ground wasn't always damp... How could the electromagnets of the receptors work with the little current produced by a few Daniels cells in series having to pass through many kilometers of desertic, high-resistance, very dry ground...?

And the thousands of kilometers of the first transatlantic telegraph, employing an unipolar cable, also used 'ground return' to complete the circuit...

 

[zoki85]

Well, I don't doubt that, in principle, but in the early telegraphs, where ground return was standard, the distances covered by the lines where often very large, and the ground wasn't always damp... How could the electromagnets of the receptors work with the little current produced by a few Daniels cells in series having to pass through many kilometers of desertic, high-resistance, very dry ground...?

And the thousands of kilometers of the first transatlantic telegraph, employing an unipolar cable, also used 'ground return' to complete the circuit...

When distances become so large, wire loses become more concern than ground return loses. Atenuation becomes so significant. IIRC, very long pulses with higher voltages are required for communication

 

[NTW]

When distances become so large, wire loses become more concern than ground return loses. Atenuation becomes so significant. IIRC, very long pulses with higher voltages are required for communication

For damp, or waterlogged ground, usual in wet countries, I find that quite plausible; but how is it possible that the 'ground return' may work in arid zones, where the ground is completely dry, and its electrical resistance extremely high...? And that for thousands of kilometers... Yes, there are aquifers even in deserts, but not everywhere, and they are often very deep...

 

[zoki85]

For damp, or waterlogged ground, usual in wet countries, I find that quite plausible; but how is it possible that the 'ground return' may work in arid zones, where the ground is completely dry, and its electrical resistance extremely high...? And that for thousands of kilometers... Yes, there are aquifers even in deserts, but not everywhere, and they are often very deep...

I find that plausible for a normal, average ground too. The point is that after leaving port, current flows deep underground and traverses large effective cross section of ground beneath. If the grounding instalation is decently enginered, a resistive part of zero sequence impedance per phase should be increased only by 0.1-0.2 Ω/km due to the resistance of ground. This is my data for 50/60 Hz system , but similar reasoning may be applied to single wire telegraphy . Certainly, you may increase wire cross section considerably and decrease it's resistance considerably to make ground loses highly dominant, but this is economically and practically bad decision.

 

[fegovi]

In my opinion telegraph transmission is not just the same that electric current, because in this case only electrical pulse are transmitted. Is not necessary to transport electrons through the wire but only changes of voltage. The receptor receive this changes in voltage and transform in an signal.
It is anything like a pipe full of water. If we change the pressure in a extremity a barometer in the other move according with the changes, but no any water move through it.

 

[NTW]

In my opinion telegraph transmission is not just the same that electric current, because in this case only electrical pulse are transmitted. Is not necessary to transport electrons through the wire but only changes of voltage. The receptor receive this changes in voltage and transform in an signal.
It is anything like a pipe full of water. If we change the pressure in a extremity a barometer in the other move according with the changes, but no any water move through it.

Perhaps a 'static electricity' telegraph such as the one you propose might work. If you charge a cable with electricity, that charge may be detected, for example with an electroscope, at any point along the cable. But I doubt that the scheme might work in practice, save in very dry weather and for short distances. In the real world, telegraph lines need a physical return, that is usually a cable, but the ground does work too...

 

[zoki85]

In my opinion telegraph transmission is not just the same that electric current, because in this case only electrical pulse are transmitted. Is not necessary to transport electrons through the wire but only changes of voltage. The receptor receive this changes in voltage and transform in an signal.

Actually, laws of propagation are quite similar. Voltage (electrical) impulse propagation also carries electrical current propagation with it. The mayor difference is short telegraph pulse is way more atenuated than 60 Hz "pulse", and more energy is lost. That doesn't matter as long as we can detect (receive) pulse. Of course, this is unacceptable in electrical power transmission.

 

[Danger]

A touch off-topic, but I believe appropriate here: I've always wondered why they didn't use the rails as a conductor rather than string dedicated wires.

 

[NTW]

A touch off-topic, but I believe appropriate here: I've always wondered why they didn't use the rails as a conductor rather than string dedicated wires.

Steinheil discovered the 'earth return' when he tried to use the two rails as transmission lines for an early telegraph. The leakage that he detected induced him to use the Earth as return...

 

[Danger]

Oh, okay. Thanks. It still doesn't make a lot of sense to me, though. I never thought of using the two rails as separate paths, because with trains having metal wheels and chassis there would be a constant short across them. (In fact, that's how crossing signals, at least here in Canada, were triggered by an approaching train.) Using them in one direction, though, seems more efficient than the wires.

 

[NascentOxygen]

A touch off-topic, but I believe appropriate here: I've always wondered why they didn't use the rails as a conductor rather than string dedicated wires.

That's an interesting alternative. Each rail would have to be electrically bonded to the next---so a lot of soldered or welded joints. Dissimilar metals in contact become sites of corrosion, and sources of galvanic potentials which may interfere with the telegraph signals.

But I'm wondering whether slightly-magnitized steel trucks and bogies clanging and banging over every rail gap might induce interference/noise emf's in the rails either by themselves or by virtue of the rails being a conductor immersed in Earth's magnetic field?

 

[NTW]

That's an interesting alternative. Each rail would have to be electrically bonded to the next---so a lot of soldered or welded joints. Dissimilar metals (...)

All electrified tracks have electrical continuity between one rail and the next. Besides, and in most present-day tracks, the rails themselves are often solidly welded together...

 

[NascentOxygen]

Of course, I was referring to technical difficulties that must be surmounted in the days of the morse telegraph. They weren't electrified rails then, were they?? The rails then may have been higher resistance than todays, too.

 

[Danger]

Of course, I was referring to technical difficulties that must be surmounted in the days of the morse telegraph. They weren't electrified rails then, were they?? The rails then may have been higher resistance than todays, too.

I'm not sure about in the beginning days, but here the non-welded rail segments are linked with steel brackets spiked into the ties. I don't know how it works with the new concrete ties, unless they're used only with welded rails.

 

[Baluncore]

Rails are bolted together using “fish plates”. The thermal expansion and contraction of the rails keeps the surfaces sliding with the bolt and spring washer holding them together, through elliptical holes. http://en.wikipedia.org/wiki/Fishplate

The problem with ground return telegraph was that the signal current was often only a small percentage of the ground induced current. Magnetic storms and electrochemical corrosion and weathering cause significant background currents.

When using a ground return circuit, the natural interference effects were often reduced by cancellation. That problem disappeared when twisted pairs of wires were introduced.

With ground return, the signal traveled along the wire above ground. That was in effect, a transmission line with self inductance and capacitance to ground. Charging and discharging the line capacitance was necessary to get the signal to propagate along the line so a current really did flow along the line, while an equal and opposite current flowed deeper in the ground.

Ground resistance is rarely a problem if the ground connections at each end are installed and maintained correctly. There is much more resistance in the wire than the ground return.

SWER (Single Wire Earth Return) lines are still used to provide HV AC power to remote sites. http://en.wikipedia.org/wiki/Single-wire_earth_return

 

[Danger]

There's a side-note that I always found amusing. In the old days, iron particles in the coal smoke from a locomotive frequently got caught up in the magnetic field surrounding a telegraph line. There were strings of black "doughnuts" hovering all over the country. :D

 

[zoki85]

In the old days, iron particles in the coal smoke from a locomotive frequently got caught up in the magnetic field surrounding a telegraph line. There were strings of black "doughnuts" hovering all over the country. :D

Maybe a stupid question, but what iron particles had to do in the coal smoke?

 

[Danger]

Maybe a stupid question, but what iron particles had to do in the coal smoke?

Not stupid at all. Coal is not pure carbon, and far less so in the 1800's. When it was burned, a lot of the impurities went up the chimney. What was left was mostly iron in the form of "clinkers", but some of it escaped.

 

[Baluncore]

In the old days, iron particles in the coal smoke from a locomotive frequently got caught up in the magnetic field surrounding a telegraph line. There were strings of black "doughnuts" hovering all over the country.

In https://www.physicsforums.com/threads/ball-lightning.454565/page-2

In a way, this is reminiscent of a very well-known documented phenomenon from the early days of telegraphy. Iron particles from the smoke of coal-fired steam locomotives used to get caught up in the magnetic fields surrounding telegraph lines (which always paralleled the tracks) and end up as glowing "doughnuts" strung along the wires like beads.

Can you please give us a few references to that “very well-known documented” – “glowing doughnuts" phenomenon.

 

[Danger]

Can you please give us a few references

No. It was recounted in things like local newspapers and probably CPR internal communications. There were undoubtably photographs, but I have no Idea as to whether or not any survive now. It was known in my family because my grandfather was on the CPR team that built the line from Calgary to Lake Louise (Louise Junction in those days) and mentioned them frequently. He died before I was born, but just about everyone in my family also witnessed the phenomenon since the line ran through our town. The trains lingered for a while both for loading and unloading and because we were a watering station for the boilers, so there was more time for the things to develop.

edit: I didn't mean to imply that the wires existed before the railroad was completed, but he continued to work along it for his whole life.

 

[NascentOxygen]

Not stupid at all. Coal is not pure carbon, and far less so in the 1800's. When it was burned, a lot of the impurities went up the chimney. What was left was mostly iron in the form of "clinkers", but some of it escaped.

Would this iron have been introduced by wear from steel tools in the coal's mining & crushing process?

 

[Danger]

Would this iron have been introduced by wear from steel tools in the coal's mining & crushing process?

I've never thought about it. I doubt it, though, considering how much of it there was. (Or maybe most of it was something other than iron.) I just always assumed that it was a physical mixture that occurred during the formation of coal from biomatter in an iron-rich environment. My only personal experience with it was that we always had to shovel "clinkers" which resembled very porous, reddish, heavy meteorites, from our coal furnaces and stoves when I was a kid. I thought that they were iron, but maybe not. Maybe the "doughnuts" were some other magnetic material as well. Perhaps someone else in my age range or beyond can shed more light upon the subject.