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Firstly, this is NOT a duplicate question. There have been similar questions asked, but no one has adequately explained this particular aspect of electric generators. Yes, they act as an electron "pump", moving local electrons through their coils via magnetism. The issue here is supply. Being that ground is likely the return conduit, and being that air is supposedly an insulator, and being that a complete circuit is necessary for electron flow, how are electrons moving INTO the windings of a generator?

I would assume that air is not a perfect insulator, and that there is some ambient atmospheric electron flow, and that the electrons being pushed through the windings of a generator are pulled from the local atmosphere; but I haven't found this written down anywhere or alluded to.

If this is the case, then electric generators shouldn't work for very long without an atmosphere. If this is not the case, then, if not the from the local atmosphere, then from where are local free electrons being pulled?

A generator does not create electrons, and copper windings can only initially contain some finite amount of them. Electrons are pulled from and move through the atoms of various elements (some better than others, obviously), so how could electrons flow in a (perfect, uncontaminated, unmodified) vacuum with no medium (atoms) to flow through?

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  • $\begingroup$ See my updated answer estimatiing the amount of electrons in the copper windings of a generator. $\endgroup$ – Bob D Jul 6 at 8:55
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I don't see why air or vacuum is a consideration. If you want a generator to produce a current you have to hook it up to a complete circuit.

Say you want to light a bulb - connect one terminal of the generator to each terminal of the bulb. The generator pulls electrons out of one end of the bulb's filament and pushes them into the other. The electrons don't have to come out of the air. You'll never run out of electrons you just keep pushing the same ones around and around.

You could ground one of the terminals of the generator if you want but it won't make much difference the electrons are just going around the circuit.

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120 volt electric generators do not rely on a ground connection in order to transport electric power. The ground connection is for safety purposes, in case of a wiring fault. Ordinary electric generators do not pull electrons out of the air. Instead they pull electrons out of the neutral return line (color code white), raise their voltage, and pump them out the hot line (color code black). Meanwhile, the safety ground line (color code green) ordinarily carries no electron current at all.

Electric current cannot flow through a vacuum unless the electrons comprising it have been boiled out of a hot wire (thermionic emission, as in an old-style TV picture tube), ejected from the wire surface by ultraviolet light (photoemission) or pulled out of the wire surface by a highly anisotropic electric field (field emission).

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Imagine that instead of an electric circuit it was a water circuit. You had tubes full of water in place of conductive wires.

Your generator was like peristaltic pump. For DC current it would pump in one direction. For AC it would pump back and forth.

The tubes could be entirely closed with no place for water to leak out or leak in.

The pump creates high pressure on one side and low pressure on the other. The water moves to reduce that pressure.

It looks like pretty much an exact analogy to me. The water molecules are moving very fast in random directions, and the pump moves them slowly on average in a particular direction.

There's no mystery here.

You can open up the tubes by connecting a tube to the water table. If you connect it on the low-pressure side, water can get sucked from the ground, or pushed into the ground, and it won't make much difference. You don't want your water tubes to be open to the air because then high-pressure water could squirt out, or low-pressure water would suck in air bubbles. I think by that point the analogy has broken down.

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Electrons are not circulated continuously in one way. In AC generators this is already how they work, i.e. electrons move one way half of the cycle and the other way in the rest of their cycle. The magnets rotate to achieve this "Alternating Current." In DC generators this is achieved by the change of the connectors through brushes at two poles of the circuit. Thus the electrons are pumped to the circuit in the negative pole when the brush containing electrons generated by the magnets are at that brush and when the magnets turn to create positive charge at that brush, the positive pole of the circuit is connected to the same brush i.e. the electrons supplied by the circuit (returning from the circuit at low potential) are sucked inside the generator.

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In alternating current generators, electrons do not move remotely, but vibrate back and forth near their equilibrium positions. That's what AC is like. Generators have nothing to do with air and don't need extra electrons.

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Your basic premise that the generator coils need to draw in electrons from their environment (the ground or air) is incorrect.

The electrons in the metal coils of the generator are highly mobile and are sometimes referred to as a “sea” of electrons. These same electrons move around in the circuit connected to the generator. Electrons are not supplied to or taken away from the generator coils.

A generator does not create electrons, and copper windings can only initially contain some finite amount of them.

Out of curiosity, I wondered just how "finite" the amount of free electrons in the coils of a generator is. That is, I wondered just how many free electrons might there be in the coils of a typical power plant generator. Based on some rough calculations, I came up with an estimate of about 50 x $10^{13}$ Coulombs of charge (see data below). Given that one ampere is 1 Coulomb/sec, if I and the sources of my data are correct there appears to be an ample supply of free electrons in the coils of a typical power plant generator.

The key fact is item 3 below. From there it depends on how many cubic meters of copper are used in a typical power plant.

Given an ample supply of free electrons, the only thing needed is energy to move the electrons around in a circuit. The generator uses rotational kinetic energy from a mechanically driven motor to cause relative motion between its coils and a magnetic field thereby generating an emf (voltage) according to Faraday’s law of electromagnetic induction. The rotational kinetic energy of the motor is, in turn, obtained from some primary energy source (fossil fuel, nuclear, solar, wind).

Hope this helps

  1. Copper free electron density: 8.47 x $10^{28}$ electrons/$m^3$
  2. Electrons per Coulomb: 6 x $10^{18}$
  3. Coulombs per $m^3$ (1 divided by 2) : 1.4 x $10^{10}$
  4. Copper per MW of power generation (mid range- depends on generator type): 500 Kg
  5. Density copper: 9 $kg/m^3$
  6. Coal fired power plant (typ):600 MW
  7. Free electrons in coils of said plant (calc from above): 46.2 x $10^{13}$ Coulombs
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Grounding one of the output wires of a generator is not for drawing electrons from earth! It's not a MUST to ground the wire. It's only for safety.

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Electrons cannot move through a perfect vacuum. There are methods of inducing current in a vacuum, but they involve contaminating and modifying the vacuum (meaning it's no longer a true vacuum). So yes, according to the process of elimination, air, that is, atmosphere, must be inherently conductive enough to act as an electron flow medium during the process of electron flow generation via magnetism and conductive windings.

Though this would leave the question of whether different atmospheric conditions (humidity, temperature, atmospheric composition) have any measurable effect on the efficiency of electric generation via magnetism and conductive windings. (temperature itself will affect the conductivity of the windings, with cooler temperatures increasing conductivity, and warmer temperatures increasing resistance; so this would need to be accounted for as well)

edit: it would also also leave the question of whether a grounded generator would be measurably more efficient than an ungrounded generator, all other things being equal.

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  • $\begingroup$ " So yes, according to the process of elimination, air, that is, atmosphere, must be inherently conductive enough to act as an electron flow medium during the process of electron flow generation via magnetism and conductive windings." sorry, but this is not correct. see the answer by Niels. A generator would work even in vacuum as the current that flows in the circuits is just within the circuits, moving with the drift velocity induced by the voltage differences hyperphysics.phy-astr.gsu.edu/hbase/electric/miccur.html $\endgroup$ – anna v Jul 6 at 5:06

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