Sketch per-phase equivalent circuit of power system, find excitation on the generator and short circuit current.
A 3-phase synchronous generator is connected to a step-up transformer T1, which is connected to a 60km long transmission line. As far end of the line, a step-down transformer bank T2 is connected. The secondary of T2 supplies two loads L1 and L2.
The ratings for the various parts of system are as follows:
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Generator
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10 MVA, 12kV, X = 20%, star connected
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T1
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5 MVA, 12/69 kV, X = 10%
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T2
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5 MVA, 69/4.16 kV, X=10%
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L1
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2000 kVA at 0.8 pf lagging
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L2
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1000 kVA at 0.75 pf lagging
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Transmission Line
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X = 0.5 W/km (R is negligible)
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A. Draw per-phase equivalent circuit of the power system showing all reactances in per unit and show the base voltages used at various parts of the network. Use 10 MVA and 12 kV as base quantities in the generator circuit.
B. If the voltage on the load bus bar has to be maintained at 4.16 kV, find the required excitation on the generator.
C. For this excitation, establish the short circuit current (in amperes) when a three-phase fault occurs on the secondary winding of transformer T2.