electric-circuitselectricity
We know that if Single Line to Fault occurs, then fault current flows to the earth. I want to know whether the current will return to the source or not. For the current to flow we need a closed path.
How it is possible for current to flow in a open circuit if you say that current does not return to the source.
To start with one could have an ac current never grounded anywhere , for a household generator for example. The reason one grounds at the generator is for safety so the ground can pick up any miss chance, as it is a practically infinite sink for electrons. Only one of the two lines can be grounded of course :).
It was found though that due to capacitences the ac neutral even though it starts with zero at the ground ends up in households with some voltage difference dependingon the distances traveled from the last grounding of the supply circuit. I have measured up to 45 volts to the ground difference on the neutral in the 220 we have here.
The household is grounded to some water pipes etc for the same reason it starts grounded, so the outside of appliances is safe for the casual user from small accidents.
However IF at the service panel, the neutral was not connected to earth ground (so the neutral left floating), then we definitely don't have a closed circuit, yet my intuition tells me somehow current would still flow into earth in a short circuit condition.
Sure, due to the infinite sink for electrons of the earth of course the circuit will close to the ground whether the short circuit was from the neutral ( floating) or the live, both would be live in this hypothesis. Grounding at the factory/generator is for safety of use, reduces probabilities of fatal accidents, and in order to assure a stable voltage difference to the user, not floating where then the accidental shorts would be more dangerous. As it arrives floating a bit by the effective circuit the current traverses to the homes, houses have to be grounded again for safety reasons. Having one of the two wires close to ground voltage reduces probabilities of accident by 1/2
Here is what happens if the $300V$ wind generator tries to create a current in the wire.
At first some electrons will move e.g. to the right in the wire above.
However this leaves one end of the wire positively charged and the electrons are attracted back, within a short time the $300V$ would not be able to move any more electrons and the current stops.
So a closed circuit is necessary for a current to flow.
Best Answer
The word "Earth" is sometimes misleading. I think (if I get the sense of your question right), it is more properly called a "Protective Earth". In home electricity supplies, one side of the supply is "tethered" to the same potential as a protective earth circuit. This latter is simply a system of conductors, going through the third "Earth" pin on the socket outlet, that tethers any conducting surface of an electrical appliance to the one (called the "Neutral") side of the supply. The other side of the supply is called the "active".
If a fault happens in an appliance such that the active touches the conductive housing of an appliance (say of a toaster), we have a dangerous situation, since anyone touching the appliance can then get an electric shock. However, if the housing is connected to the protective earth circuit, there is a redundant path back to the supply's neutral. This leads to a high current in the redundant path and hopefully a blown fuse in the supply live.
A more modern and safer way to achieve this protection is earth leakage protection - a system that detects, through the Ampère-law-begotten "magneto motive force MMF)", when the current through the active is different from that through the neutral. In this system, both active and neutral lines pass through a torus-shapen ferromanetic core. If the current in one doesn't match that in the other (i.e. the current going into the appliance through the active is not the same magnitude but exactly out of phase with the current coming out through the neutral), then there is a nonzero $\oint \vec{H}\cdot{\rm d}\vec{\ell}$ ("magneto-motive force") around the core and thus an AC magnetic field though a sense coil wound threading the torus- by Faraday's law, this begets an EMF in the sense coil which trips a circuit breaker. These devices can be made very cheaply and are extremely effective - shutting off within milliseconds if an imbalance of more than typically $50{\rm \mu A}$ is sensed.
Lastly, electric current can in general flow without a return path through the mechanisms of displacement current and capacitance. See my answer to the question "Does alternating current (AC) require a complete circuit?" for details.
Lastly, there have been some really bizarre truly one-line power transmission systems thought of in the past, where the one line works as a waveguide and does not need a return path. See the Wiki Page for the Goubau Line for details.