The single-line diagram of a three-phase power system is shown below. Bus 1 Bus 2 2+1 1+ a T₁ T₂ G₁ Line 2 Line 1 Line 3 Bus 3 T3 Bus 4 Load Figure 1 The manufacturer's nominal ratings are given as follows: G₂

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The single-line diagram of a three-phase power system is shown below.
Bus 2
Q+01 10+Q
T₁
T₂ Y
Bus 1
Device
Generator G₁:
Generator G₂:
Transformer T1:
Transformer T2:
Transformer T3:
Line 2
Line 1
toot
Load
T3
S₁
48 MVA
25 MVA
50 MVA
30 MVA
50 MVA
Line 3
Bus 3
Figure 1
The manufacturer's nominal ratings are given as follows:
Bus 4
(L-L)n
20 kV
13.8 kV
20/110 kV
13.8/110 kV
11/110 kV
X₁
20%
15%
8%
6%
10%
(Note: Of course, the Xn in each row is the per-unit value impedance of that equipment
when using on the Sn (Capacity of that equipment) and the U(L-L)n (Line-to-line voltage of that
equipment) of that row as the MVA base and the voltage base.)
The balanced three-phase load at bus 4 absorbs 60 MVA at 0.75 power factor (lagging), and
lines 1, 2, and 3 have the reactance of 400, 32 Q, and 300, respectively.
(a) Using the common base Sb = 50 MVA, draw the impedance diagram in per unit
including the load impedance.
(b) Now there is a solid balanced three-phase short-circuit fault at Bus 4, estimate the
fault current at the fault location, in unit of Ampere. Assuming that, at the time of fault,
the voltage output values of G1 and G2 are 20kV and 13.8kV respectively. (Hints,
you may use superposition theory).
(c) Based on the calculation result of part (b), what should be the minimum breaking
capacity (in unit of MVA) for the circuit breaker which connecting Bus 4 and the Load.
Transcribed Image Text:The single-line diagram of a three-phase power system is shown below. Bus 2 Q+01 10+Q T₁ T₂ Y Bus 1 Device Generator G₁: Generator G₂: Transformer T1: Transformer T2: Transformer T3: Line 2 Line 1 toot Load T3 S₁ 48 MVA 25 MVA 50 MVA 30 MVA 50 MVA Line 3 Bus 3 Figure 1 The manufacturer's nominal ratings are given as follows: Bus 4 (L-L)n 20 kV 13.8 kV 20/110 kV 13.8/110 kV 11/110 kV X₁ 20% 15% 8% 6% 10% (Note: Of course, the Xn in each row is the per-unit value impedance of that equipment when using on the Sn (Capacity of that equipment) and the U(L-L)n (Line-to-line voltage of that equipment) of that row as the MVA base and the voltage base.) The balanced three-phase load at bus 4 absorbs 60 MVA at 0.75 power factor (lagging), and lines 1, 2, and 3 have the reactance of 400, 32 Q, and 300, respectively. (a) Using the common base Sb = 50 MVA, draw the impedance diagram in per unit including the load impedance. (b) Now there is a solid balanced three-phase short-circuit fault at Bus 4, estimate the fault current at the fault location, in unit of Ampere. Assuming that, at the time of fault, the voltage output values of G1 and G2 are 20kV and 13.8kV respectively. (Hints, you may use superposition theory). (c) Based on the calculation result of part (b), what should be the minimum breaking capacity (in unit of MVA) for the circuit breaker which connecting Bus 4 and the Load.
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