Earth Fault

yes, the fault current will flow. But fault is random, the type , size are random. Substation mostly earthed with grid method if it is not ground, i think it will be dangerous. Let say, the substation is totally not earthed, my opinion is there will be arching. cmiiw

Dont confuse me saying random,arching blah blah. Tell me technically with explaination.

good try, but you dont know...read your third sentence again.

There is confusion when you use the term earth. Are you referring to earth(dirt) or are your referring the the neutral of the system. An earth(dirt) fault has a high resistance and current flow is a low value. A Phase to neutral(sometimes called ground) fault will have a low impedance and the current flow is a high value. Regarding distance, the fault will flow back to the source. Earth(dirt) is not a "sink hole" and does not absorb the fault current.

The amount of current will depend upon the 'earthing resistance' and the potential difference (i.e. the voltage).

The current really flows to the ground and it can actually be measured by an ammeter (or a tong ammeter) if an experiment is performed.

The horizontal distance is theoretically 'zero' because the current actually flows to the core of the earth. However, this can happen only if one of the terminals of generation of the substation / source is earthed (or, in case of multi phase generation, the neutral point obtained by the star connection of the phases is earthed).

In case the entire system including generation is totally isolated (i.e. and operating in vacuum or humidity air - ensuring 'zero' earthing of the substation at all the points / terminals), there would be no current flowing to the earth at all.

Ashok Shukla

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Earth and neutral are bonded at the substation.

Any fault current via earth will be via the neutral and if the current exceeds the breaker trip value (but only then!) the breaker will trip.

In modern installations, it is usual to also have an ELCB or similar that will trip if and when a few milliamps of fault current flows via the earth wire to the neutral at the substation. This is to stop people being electrocuted by a partial fault where the current is not enough to trip the main breaker.....

In some countries, the breaker combines both sensing I believe.

In some countries the earth is via the ground.....this cannot be as safe......but I have no personal knowledge of such systems......I can only speak about what happens in Europe.

The answer is YES.

Your follow up question is not straight forward. One my function at work is to calculated the current that flows through earth and back to the grid. The following are what I consider:

1. Soil Structure - Not only is the soil resistivity important, but the different layers must be considered. You have to determine the reflective coeifficents between layers to work out the earth potential rise.

2. The tower footing resistance - this can be measured on site or calculated.

3. The line impedance must be calculated under single phase fault. Note that the earth wire or neutral with have considerable influence due to mutal coupling.

4. Substation grid impedance

5. Network source impedance

I use a software tool, CDEGS see www.sestech.com , to model the substation, soil and lines. Your model has to be as close as practically possible to the real world.

Third question - substation is always earthed, just in different ways to limit the fault current. Substation is never floating.

Your last question, the earth is a lumped impedance in a ladder network. The current always flows back to the source impedance.

I cannot do justice to this topic in this forum, however I hope this helps.

In case of earth fault the earth acts as conductor. The faulty cable / conductor gets connected through the earth to the substation originating point. The earth acts as a retun conductor and depending on the quality of earthing ( earth resistance of earthing electrode) the current flows. The distance can be lage and the quantum of current depends hogood is the soil for conducting. If the terrian is rockey the current will be less as the earth conductivity shall be less. In rainy season the conductivity is better as the conductivity improves.

The distance can be large as depending on the distance the resistance increases and the current accordingly reduces on the return path

That might be true for India, its certainly not true in Europe....

The only places I have heard of with earth return are some 1 wire systems in the Australian outback, where earth is the return of all current as only a single wire is run to the farm or whatever. I was told that some parts of S.Africa use a similar method....

Perhaps an "Outback Aussie" can chime in here and let us know exactly what is done there.

If you use a 3 wire system (Ground, neutral and phase) then having the earth return via the planet earth is going to be exceedingly dangerous......

Here in Europe the earth wire is bonded to the planet at each house (and to the copper water piping etc), but we do not rely on that providing enough of a good path, there is also a good bit of copper taking the earth return back to the substation....

As far as I remember, the only reason that the house earth cable is also bonded to the planet is to stop unbalanced phases causing a rise in the neutral/earth connection relative to the planet.......but I stand corrected if a knowledgeable person can show me differently......its been a few years.

Many people with 3 wire systems "believe" wrongly that the ground wire is conducting via the planet because of the name of the wire......

Great reply, I will give you a GA for bringing me up to speed on single wire transmission again, I sort of knew it about 40 years ago, but was totally unsure till your Post arrived!!!!

Many thanks.

GA.