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Fault Current calculation

by I_am_learning
Tags: calculation, current, fault
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I_am_learning
#1
Apr18-11, 11:22 PM
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P: 669
Last time I was talking about Isolated Voltage, and some of you people were really helping me about, but I posted (did) something stupid and got the thread deleted.
I am sorry for that.

Now, I want to talk about my confusion in a different (safe) way.


The above figure shows a distribution line along with a Pole. I understand there exist capacitance between lines (shown in pink) and between lines and ground(shown in green) if we treat the earth as an infinite equipotential surface (conductor). Also the pole is grounded. But please note that the neutral of Distribution Transformer isn't grounded. Also assume that no grounding is done in any other part of the system.

Now, the question is what happens if one of the lines break and comes in contact with the body of the pole? How much fault current will flow?

Thanks.
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I_am_learning
#2
Apr19-11, 11:59 PM
I_am_learning's Avatar
P: 669
The point I am unsure off is, can I calculate the fault current based on above model (capacitances between lines and Between line and earth) only OR I have somthing missing in that model?
If I follow only that model, the fault current will not be significantly large, only the capacitor between the faulted Line and earth shorts out. The faulted line is still capacitively Isolated from other lines.
Do the circuit breaker trip?
aks786
#3
Apr22-11, 08:52 AM
P: 28
in this circuit , fault current would depend on capacitance of healthy phases with ground. capacitance of transformer winding with tank(which would be grounded) will play significant role.

current would be proportional to system voltage. and for low voltage <1kV current would be insignificant.

I_am_learning
#4
Apr24-11, 10:41 PM
I_am_learning's Avatar
P: 669
Fault Current calculation

Ok, instead of one of the phase shorting to the pole, If a monkey sitting on the pole touches one of the phase how much (tentative) current will flow?
Its again dependent upon the various capacitances and, I think its magnitude will be insignificant.

The reason I am being not totally sure is because someone here had previously told me that the Earth isn't something to be taken just as a plain conductor. It can sink in huge currents, weather you close the circuit or not!!! Its actually at 0 potential he said, and that anything that comes between earth and high potential will be burned down.

I don't have enough reason to agree to that.


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