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Hello All,

1.Star connected earthed neutral Source to Star connected earthed neutral load? Say if a L-G fault occurs between the source and load, How does the fault current gets distributed? To the source side neutral or load side neutral?
2.Star- Star Transformer. Neutral earthed on both the primary and secondary. say If a L-G fault occurs on secondary side, does the fault current flow in to the primary side neutral too? How does the fault current reflected in the primary?
3. Star- Delta Transformer. Neutral earthed on Star side. say If a L-G fault occurs on Delta side, does the fault current flow in to the star side neutral? How does the fault current reflected in the star side.

Thanks beforehand.
 
OP is in India, so may be just seeking knowledge.
 
The fault current takes the path of least resistance, dependent on the natural resistance in that path and the current flowing, it may build up heat creating resistance and thus the current will flow down an alternative path with less resistance if available until the original choice path cools down and become the primary route again.. this all happen in nano seconds repeatedly and is what gives unified distribution of current in a ring main dependent on its location in the circuit.
 
The fault current takes the path of least resistance

AC, Impedance actually :)
Question for you, a multiple path circuit, how and when does the current 'know' in what quantity to flow down each path? Take several impedances in parallel, emf at one end, open circuit at other, then make the circuit.
 
AC, Impedance actually :)
Question for you, a multiple path circuit, how and when does the current 'know' in what quantity to flow down each path? Take several impedances in parallel, emf at one end, open circuit at other, then make the circuit.

Impedance - Yes you are correct just a bad habit of mine as all my control circuits are normally DC doh!

To answer your question isn't as simple as you may think and at an atomical/quantum level it is very complicated but in the macro world where we can measure repeatedly and get results, where we can use mathematical equations to predict the values it would seem straight forward but it is far from it.
The easiest way to show you what does happen is to watch a plama disc where you can view the electricity trying to get from source to destination, although its not exactly how it works it does show that as the flow heats up a path, it in turn becomes a higher Impedance/resistance than an alternative route so the Electricity will repeatedly alter and adjust it path to the lowest impedance/resistance which heats up and the cycle repeats.. these plasma discs show in slow motion what happens billions of times a second in a standard multiple routed circuit.

 
The fault current takes the path of least resistance, dependent on the natural resistance in that path and the current flowing, it may build up heat creating resistance and thus the current will flow down an alternative path with less resistance if available until the original choice path cools down and become the primary route again.. this all happen in nano seconds repeatedly and is what gives unified distribution of current in a ring main dependent on its location in the circuit.
No, it wil take all available paths.
There will be lower current along higher resistance paths, but it will still be there.
This is similar to the current flow in a RFC.
Socket at mid point will have equal current on both legs.
Socket a quarter round the ring will have 75% current on the short leg and 25% on the long.
 
I should have worded it better @spinlondon, I wasn't implying all the current went one way then another then another etc although to say such isn't exactly untrue either depending how deep into the quantum world you wish to go, but for the sake of the context of the question you are correct in that all possible routes where a PD exists and is conductive will see a flow of current, I meant it is averaged out across the possible routes proportionally to resistance/impedance met. In reality current flow isn't electrons whizzing around the wires as many think its just a propagation of the electromagnetic wave at this level resistance/impedance, although the electrons do migrate at a very slow pace as a result in dc and just wiggle back and forth in AC about their position.
The propagation of such a wave doesn't follow the same rules which we imply above but because it happens trillions of times we percieve it as all routes and it simplifies things for learning.
Sadly or luckily depending on what your trying to read, our instruments cannot sample the current flow millions of times per second so just give a very very crude mean average which in the Macro world is good enough to be used to design circuits and calculate cable sizes.
 
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