What is the speed of "electricity"?

Question

In a distribution grid, what is the speed of

energy
signal

Is it strictly the same?

And how is synchronisation achieved? Is an electric grid essentially an orchestra where everyone is the chief and gives the beat to everyone?

Electric current can give you an idea of how fast electricity may travel. The speed varies on the medium of which the electron travels. Hydron Colliders make protons travel at an insane amount of speed. — , Oct 28 '19 at 02:33
Related / cross-site near-duplicate: [Speed of light vs speed of electricity](//physics.stackexchange.com/a/359032) - the speed of electricity in wires is a transmission-line effect which we can model with series inductance and parallel capacitance per unit length. — Peter Cordes, Oct 29 '19 at 02:07
Isn't any research required? At the very least why this is not a duplicate? — Peter Mortensen, Oct 29 '19 at 06:15
Why this question has so many votes...so broad and overrated — Mitu Raj, Oct 29 '19 at 12:34
Heh, first define the word "Electricity." Is Electricity really just the joules; the EM fields racing along the cable? Is Electricity the coulombs of drifting electrons? Is it really just a rate (the coulombs per second? The joules per second?) Those joules are moving from source to load, one way. The coulombs move in a closed loop, staying inside a "complete circuit" path. Is electricity made of EM waves in space, or is the electricity just a bucket of electrons inside the copper? (It's like having just one word which means "wind," and also means "sound." — wbeaty, Dec 06 '20 at 05:36
@curiousguy Don't call it "electricity," instead use its real name: electromagnetic waves and EM fields. In circuits, the joules are EM waves that zip through the space surrounding the wires. Signals ARE the energy. (And electrical energy never travels inside wires.) So, ask questions about EM propagating along wires, and then your question will be correct ...and it will either answer itself, or will attract correct answers. (If people don't know that the "Electricity" is actually made of EM waves at 60Hz, then the questions/answers will turn into a morass of error and misunderstandings.) — wbeaty, Dec 07 '20 at 03:09
@wbeaty Fine; although it's "electric" or "electricity" in everyday language: "What's your electric consumption this month?" or "the electricity meter." Also I live in Europe so... 50 Hz for me. — curiousguy, Dec 08 '20 at 06:10
@curiousguy but when asking questions about physics, everyday language almost always fails. If we already knew that electrical energy is simply EM waves on wires, then no need to ask if speed of EM energy is different than the speed of EM signals (it's not.) It's only when people start believing in "electricity" that confusion arises. Util. companies are selling us EM waves. (What if this was taught in early science classes? Instead they teach kids that "electricity" is amperes, is current.) My point was that "everyday language" is what derails our basic understanding. — wbeaty, Dec 08 '20 at 10:47
@wbeaty "_everyday language almost always fails._" That's the _title_. The body of the Q explicitly mentioned "energy" (from the very 1st revision). I also mentioned the information. — curiousguy, Dec 08 '20 at 20:44

DKNguyen · Answer 1 · 2019-10-31T12:42:47.130

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For most of the copper wire and traces you see, about 60% the speed of light in a vacuum. The energy is the signal so they are the same.

The speed of electrons is much slower...slower than walking pace. The electrons aren't moving to and from the powerplant 60 times per second.

Think the difference between the speed of sound and the wind. The wave (energy) moves through the medium much faster than the medium itself.

edited Oct 31 '19 at 12:42

answered Oct 28 '19 at 01:48

DKNguyen

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It doesn’t make sense to talk about the speed of electricity in copper. The wave travels around the conductor in the medium surrounding the conductor. Hence there is a difference between copper in FR4 and copper in vacuum. In fact, the actual speed inside the conductor is very frequency dependent, i.e. it is proportional to the square root of the frequency. – user110971 Oct 28 '19 at 03:07
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About the speed of electrons being slower, an analogy: Think of a tube that's filled with marbles. If I push a new marble in one end, a marble comes out the other end pretty much simultaneously. The **signal** (= marble in becomes marble out) is near instant, but the particular electron (= marble) that you pushed in the tube hasn't actually reached the end of the tube yet. The marbles in the tube "pass the message" along faster than the marbles themselves travel. The same is true of electrons. – Flater Oct 28 '19 at 12:27
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...and in case of AC, the net distance traveled per electron zeroes out on average. – dlatikay Oct 28 '19 at 17:11
@user110971 Your comment seems to be missing something between its intro claim and what follows. You say the speed is proportional to other things... ok, fine. But why does it not make sense to talk about the speed of electricity in copper? What does not make sense about it? – Loduwijk Oct 28 '19 at 17:59
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@Loduwijk When a signal travels along a conductor it actually travels in the space around the conductor as electromagnetic waves. However it also propagates perpendicularly inside the conductor but is attenuated as it travels in the conductor. The speed in the conductor is the frequency dependent part. But when we say the speed of the signal we mean how fast the signal gets from one end of the conductor to the other. So there are two speeds. Have a look at my answer to a similar question for more information https://electronics.stackexchange.com/a/462535/110971 – user110971 Oct 28 '19 at 18:08
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I work for a power company in Oregon. We have a 1Mvdc line to southern California that's been there since (I believe) the 60's. I asked about how fast electrons travel and was told that the first electrons pushed into the wire in the 60's aren't in California yet. I know that' super inexact but it made an impact. – Bill K Oct 28 '19 at 21:48
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@BillK That reminds me of how some of the light from the sun might be millions of years old because there is so much matter inside the sun that the photons collide with it all as they make their way out towards the surface. – DKNguyen Oct 28 '19 at 21:51
@Flater that's the exact same analogy that my Physics teacher used. – Baldrickk Oct 29 '19 at 16:20
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Can you elaborate on "The speed of electrons is much slower...slower than walking pace."? – RockPaperLz- Mask it or Casket Oct 30 '19 at 01:13
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@RockPaperLizard Just the way it sounds. I forget the actual speed, but really friggin' slow, even by human standards. – DKNguyen Oct 30 '19 at 01:14
@user110971 regarding the usefulness of knowing the "speed of electricity in copper" Adm. Grace Hopper had a good working estimate: about a foot per nanosecond. We care about this a great deal nowadays, one example of this is that it's the reason we have the extremely hard cap on the distance between a USB hub and the immediately downstream device, and also the overall max distance to the furthest peripheral. It's all about the round trip time for the signal, which is governed by the "speed of electricity in copper". – dgnuff Oct 30 '19 at 02:56
No, there is no "speed in copper". The speed depends, as @user110971 said, on the _insulating material_. The speed of propagation in a rubber-insulated copper wire is only about one-third of the speed in an uninsulated wire that is otherwise identical, and about half the speed of one that is insulated in polyethylene. Tony Stewart's answer below is correct. – Mark Dominus Oct 30 '19 at 13:00
I have done this experiment with co-ax cable and a pulse generator. The idea is to measure the time it takes for a pulse to travel down the cable and return. In that sense, the answer given here is correct. – puppetsock Oct 30 '19 at 18:58
Should it be 60% of *c*? Isn't the speed by definition the speed of light *in the medium*? – Acccumulation Oct 31 '19 at 05:04
@Acccumulation yes, vacuum – DKNguyen Oct 31 '19 at 12:42

score 20 · Answer 2 · edited Jun 11 '20 at 15:10

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(added) The wave speed ratio of electricity v/c is limited by the relative permetivvity, \$ε_r\$ of insulation around the conductor for the speed, v relative to speed of light, c in a vacuum. It is also limited by the relative magnetic permeability, \$\mu _r\$ in the wire or closely coupled around it, as this would occur in magnetic components.

\$v/c = 1/\sqrt{\mu_r \varepsilon_r}\$ has nothing to do with the grid conductors and only the insulation or relative dielectric constant.

The relative constant is also called Dk for most low Dk plastics is ~ 2.3 used give a velocity ratio of 2/3 or 66% such as coaxial cable. Higher is better. I am not saying all grid coax, just most coax in general.

Much of the local distribution grid is grounded coaxial cable to reduce radio noise and lightning interference, which has insulation.

The bare wire is the nearly the same speed as free space for the speed of light in a vacuum.

how is synchronization achieved?

The grid length is fixed and static and thus easy to equalize between sources at the connection point by phase-shifting methods unless some passive power factor correction is requested.

The bigger issue is the dynamic power factor correction and load balancing where the phase-correction is dynamically changing and must be balanced to provide real power that is authorized by a higher authority with trade deals that are pre-negotiated in complex algorithms based on supply & Demand during peak and off-peak hours of the day.

You can search for books on this subject or short stories, but it is beyond the scope of your question and this forum.

Is an electric grid essentially an orchestra where everyone is the conductor and gives the beat to everyone?

The conductor is the government or independent organization that controls the cesium-time coordinated synchronization of the grid in each country.

The musicians are the generators of power on the grid.

There is also a new HVDC microgrid, developed in Toronto and co-owned by a close relative of mine that avoids these sync-issues for suppliers of alternative energy sources such as PV, & Windpower.

Here is what Wiki says, https://en.wikipedia.org/wiki/Synchronization_(alternating_current)

Non-technical description.

The actual flow is slower than a water bucket-brigade, yet faster than a stadium circular arm-wave. Imagine electrons spinning in stationary motion, but in a stimulated massless cascaded-wave at the speed of light by cascaded connections, where only the surrounding insulation Dk can slow down the absolute speed of c to v.

Technically, Speed is referred to as the Propagation velocity in a transmission line following Telegrapher's Equations.

You can play with one simulation here with mismatched impedances.

edited Jun 11 '20 at 15:10

Community

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answered Oct 28 '19 at 02:09

Tony Stewart EE75

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I hear that bare speed on a copper wire is still two thirds of light. Do you have a reference for your bare speed? – toolforger Oct 29 '19 at 07:43
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You hear wrong. – Tony Stewart EE75 Oct 29 '19 at 08:20
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Do you understand the principles and equation above? – Tony Stewart EE75 Oct 29 '19 at 08:35
The secret is for you to search why. – Tony Stewart EE75 Oct 29 '19 at 08:42
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I do understand the equation, I just don't know enough details to determine whether it is applied correctly. However, I did read that signal velocity on copper wire is roughly 1/3 or lightspeed (in the context of microelectronics), you claim that it is roughly c, I don't know where the difference is so a reference would help me (your last comment about "secret" is quite the opposite of helpful, I have to say). – toolforger Oct 29 '19 at 12:55
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User...971. Previously wrote a more technical answer before https://electronics.stackexchange.com/a/462535/110971. He already linked it in comments. electicity speed is that of the wave, not the electron particles is governed by the insulation of the medium surrounding the conductors. Or in the case of optics between Tx, Rx that affects also angle of refraction. – Tony Stewart EE75 Oct 29 '19 at 15:06
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@toolforger another useful comment is [this one](https://electronics.stackexchange.com/questions/464689/what-is-the-speed-of-electricity#comment1172582_464690) and another answer linked there. "When a signal travels along a conductor it actually travels in the space around the conductor as electromagnetic waves. ..." – crasic Oct 30 '19 at 06:17
@toolforger I was prompting you to learn how to learn by searching. Wave velocity is reduced only due to the dielectric constant surrounding the conductor and it's effect on characteristic impedance. 2/3c is typical for coax cable due to the dielectric constant of the plastic dielectric. Air is about 99% of a Vacuum but that varies with moisture in air. But actually it is more complex than this . There is a frequency sensitivity due to phase and group velocity and magnetic, μ and dielectric constants ε, as well as dispersion effects https://en.wikipedia.org/wiki/Propagation_constant. – Tony Stewart EE75 Dec 08 '20 at 03:48
@TonyStewartSunnyskyguyEE75 sorry, people have been just throwing around overgeneral references so I never got an idea of what the actual issue is. Now that you mention impedance, then yeah I understand how copper wires can be slower than light speed. The reference was talking about signal speed inside computers, I don't know whether it was talking about on-chip (then it would be the impedance of the silicon substrate) or inter-chip (impedance of the PCB); I don't know the practical values so I can't tell what exactly it was, but at least I now have a general idea what's up with that. – toolforger Dec 08 '20 at 14:53
You can always look up the material dielectric constants on Wiki and relative velocity formula. There are complex versions that vary with high frequency all the way up to optical diffusion etc But to answer your question , Falstad properties indicated the 75 Ohm transmission line speed used was 0.1949 m/ns or roughly 2/3c. That's the wave speed, not the very slow electron speed migration. – Tony Stewart EE75 Dec 08 '20 at 15:56

score 13 · Answer 3 · answered Oct 28 '19 at 12:36

You need to separate two slightly different concepts.

There is the electron drift velocity which is the speed at which the charge carriers in the wire move due to the electric field (and is basically negligible, think mm/s) and the propagation velocity of the EM wave between the conductors which is a significant fraction of lightspeed.

It is the em wave that carries the energy.

Grids are generally large enough that there is significant phase shift across the grid, but that really does not matter because you synchronise a generator the the local grid connection before putting it on line.

The modern way is with all sorts of digital doings, but it can be done with a big three phase switch, a set of suitable light bulbs and a hand throttle. You wire the bulbs across the big switch so they pulse as the grid and generator slip into and out of phase sync, trim the throttle to get the pulsing to become very slow, then just as the lights fade out you throw the switch.

Closing the switch puts the machine on line and locks it in sync with the grid, if it was slightly slow it will motor (absorbing power from the grid) to get up to speed, if slightly fast it will generate until the speed matches the grid. You want to be close before you close the contactor because the currents that can flow if you are not close will cause forces that can throw the generator off its mountings (Even if it is a power station generator).

Note that at this point the machine is connected to the grid, spinning in sync and at the same SPEED as ALL the other generators on the grid, but probably has the throttle only open sufficiently to make up for friction, to make power you now need to open the throttle.

Now assuming any given generator is a small part of the grid, what happens when you throttle up is interesting, because the speed does not change (modulo any increase in grid frequency which impacts all generating stations equally), but you start pouring torque into trying to accelerate the whole grid (raise its frequency).

If you image a rotating reference plane defined by the magnetic field from the grid connected stator coils then at idle the rotor is aligned with that field so there is no torque between them. When you open the throttles the rotor eventually settles to a new angle relative to the rotating field such that the torque from the interaction of the fields exactly matches the torque from your drive. The rotor leads on the field when generating, and lags when motoring.

My father once told me that when he was a student he got to visit a power plant when they phased it in. This was in Russia, and they didn't really "phase" it in so much as just force the plant to synchronize by slamming a makeshift switch (huge bar of copper) in place (a slab of copper with a rough bar shaped hole in it) with *explosives*. He told me the power lines were making unearthly noises, and the power plant it self was screeching in a most terrifying cacophony. But it all quieted down over the course of half a minute. Thats how not to do it. — Stian, Oct 28 '19 at 13:26
@StianYttervik butttt it worked right? lol Utterly practical. — DKNguyen, Oct 28 '19 at 14:23
@Dknguyen the story doesn't say, but I would think so. If it was today, probably every fine electronic device on the kola peninsula would be fritzed and the respective houses on fire — Stian, Oct 28 '19 at 16:41

score 11 · Answer 4 · edited Oct 28 '19 at 21:04

Apart from the actual electric grid part of the question, I think you might have a confusion about the speed of electrons and the drift velocity.

What I'm saying is, when you say speed of electricity, I think you mean the speed of current, which is pretty fast, or the speed of electrons, which is also pretty fast, or the drift, which is pretty slow. (Pretty fast means near c, pretty slow can mean as slow as a snail)

score 4 · Answer 5 · answered Oct 29 '19 at 20:21

And how is synchronisation achieved? Is an electric grid essentially an orchestra where everyone is the chief and gives the beat to everyone?

For the second part of your question, check out ANSI type 25 relays, aka 'sync check' relays.

To synchronize a generator to the bus, you need to match three things: voltage magnitude, voltage phase, and voltage frequency.

An auto-synchronizing relay (25A) works by comparing the magnitude, phase, frequency of the generator output and the bus and then a) sending control signals to the prime mover (generator) to increase or decrease fuel feed to speed or slow the shaft rotation, which allows it to match both the generator phase and the frequency to the bus; and b) sending signals to the generator's voltage regulator to adjust field current to match the generator output voltage to within some percentage of the bus voltage.

A basic sync check (25) relay works by simply signalling when the above conditions are met.

Once the conditions are met, automated switchgear or a human operator can close the breaker.

If you don't properly sync, you can put incredible stress on the prime mover and windings. For example, if you are out of phase when you try to close the breaker, you're essentially dead-shorting all three generator phases at a high voltage to all three bus phases at a low voltage. As the magnetic fields try to lock, the shaft twists and the unit is potentially damaged.

score 1 · Answer 6 · answered Dec 06 '20 at 03:30

Once a generator is synchronised (and you'd do your best to get it about right before throwing the switch), if it tries to exceed the speed of the other generators on the power grid then it will be more heavily loaded (in simple terms it's trying to power the load earlier in each cycle than the other generators) and so it will tend to slow down. Conversely, if it starts to run a little slow then it will be loaded less, or even driven by the other generators to keep it up to speed. Thus when the load changes, it's sufficient for just one generator to adjust the amount of energy it's contributing and everything else will balance itself out.

What is the speed of "electricity"?

6 Answers6

Non-technical description.

Technically, Speed is referred to as the Propagation velocity in a transmission line following Telegrapher's Equations.

Linked