Question

(30) Assume that a distribution substation, shown below, has a 4000 kVA 69/12.47 kV LTC 4) transformer feeding a three-phase four-wire 12.47 kV distribution system. The transformer has a reactance of 0.065 pu. Assume that fault impedance is 40 Q and that the maximum and minimum power generations of the system are 600 and 360 MVA, respectively. Use 1 MVA as the three-phase power base: a) Under the maximum (system) power generation conditions, determine the available three- phase, L-L, and SLG fault currents at buses 1 and 2 in per units, in amperes, and in MVA. b) Under the minimum (system) power generation conditions, determine the available three- phase, L-L, and SLG fault currents at buses 1 and 2 in per units, in amperes, and in MVA. V2 Substation transformer Feeders 1 To urban distribution 2. System (source) 3 To rural distribution A-Y 2

Answer 1

2 'Sace feedercs rsal iven 4 MVA 4000 KVA Lh.ri/ .065m Trangerrner = 40 atom 4 Maimum Pouor goner inimum fou enerabór - 360 MVA Mamum Syslem unders LVA Base at 4MVA X O.065 Taoners O65 x 1 O Xnew 4. Oo01625 600 MVA at Fault gmbedonce Zç = 40S2 40 x600 5 P.n - ulw

al GOOMVA 0.008Pn 5 x GD 1 6oo three phase duutt Curesen o.01625 61.53m 61.53X 1 Vx12-17 285 VA - 2850 A Lime to Line dault O01625+ O-008 72.O8 Pu 72.08x 1 (A) 312047 33 4- KA 3340 A

Cault g- Lime to round O. O1625 + O° O08 - 125 Pn 125 x 1 = 1.05 kA - 1050 A at LMVA Tranyormer Xニ0.01625 3 60 MVA at 4052 40 x 360 12(62 3.02 out 360 MVA Zf 3 O2 3.02 x 1 360 So, as the Answer A is Samme Same Conieg Because zf ia