Fault Level

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The fault level at a point is that current which would have caused 100% voltage drop, upto that point, in case, a bolted-type-arcless zero resistance short-circuit is created at that point.

An example - A system fault level at a point is 125 MVA. Then system impedance upto the point is 1/125 = 0.008 p.u. per MVA or 100/125 = 0.8% per MVA.

Dear guest nothing is difficult to learn - there should be desire in you to learn. However to learn this subject your basic understanding of AC system is necessary and good knowledge of mathematics. Short circuit calculations are simple provided basic knowledge is gathered.

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Most of my education relevant to Electronics was done like this.

Del

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Fault Lvl Calculation :

01. Main Xmr - 6 MVA , 66/11 KVA , 7.75 % impedence.

02. Cable 300 sqmm, HT , XLPE - 20 mtr.

First convert all component in to per unit MVA rating.

(A) Xmr 6000 KVA :-

MVA value = MVA rating / Impidence (Z)

MVA value = 6 / 0.0775 = 77.41 MVA

(B) 66 KV Cable MVA :- MVA Value = MVxMV / Z

MVA Value = .066x.066 / 0.002, assuming Cable impidence is 0.2,

MVA Value for cable = 2.178 MVA

Total System MVA ( Fault level ) = A + B = 77.41+2.178 = 79.588 MVA say 80 MVA