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what is the effect of earth foult?

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emadshaaban

Electrical
Nov 2, 2011
59
dear electrical experts,
what's the effects that could appeare in case of eath foult current flows through the ground network coused by deffected motor (the system has no eath foult protection for tripping)?and how could that afect to the power generator?
 
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I think it is a basic short circuit analysis question. You'll needt to consider the grounding configuration of the generator and connections (delta, wye, grounded wye) of any intervening transformer.

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(2B)+(2B)' ?
 
thx elecrticpete, but i got it yet. The system has one three phase generator with out neutral .
 
I've seen this one before.

On the face of it, not a lot happens. You might get a bit of scorching at the site of the fault, but things generally keep on working. When I had it happen to me, the machine had been running for half an hour before somebody spotted an abnormal reading on the earth fault detection system during routine rounds.

You've used up your tolerance to a single earth fault - if you get another fault on a different phase, it's going to go bang.

You've also lost any phase to earth electric shock protection you thought you had (though I've never had much faith in this).

A.
 
Yes, ungrounded system with single earth "fault" - no fault current flows. Not even scorching at site of the fault that I have seen.

Ground detector is actuated and prompt action should be taken to determine location of the fault and remove the component from service to clear the ground alarm.

Prompt because
1 - in steady state, the voltage to ground on remaining phases increases by sqrt(3).
2 - the system may be vulnerable to the infamous dreaded intermittent arcing fault which in theory under certain conditions can cause transients of ground-referenced voltages that escalate much higher.



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(2B)+(2B)' ?
 
Also #3 as mentioned, a fault on another phase (possibly due to increased stresses from 1 and 2) will cause actual fault current to flow.

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(2B)+(2B)' ?
 
The charging current of the system capacitance and the leakage current flows. In a system of any size this current will be at least several times the lethal current level. This charging and leakage current is also the source of the discontinuous current that may develop destructive over voltages.


Bill
--------------------
"Why not the best?"
Jimmy Carter
 
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