The equipment ratings for a five bus system are given as
Generator G1: 50 MVA, 12 kV, Xd ’’=X2=0.20, X0= 0.10 per unit
Generator G2: 100 MVA, 15 kV, Xd ’’=0.2, X2=0.23, X0= 0.10 per unit
Transformer T1: 50 MVA, 10 kV (Y)/138 kV (Y), X=0.10 per unit
Transformer T1: 100 MVA, 15 kV (∆)/138 kV (Y), X=0.10 per unit
Each 138 kV line: X1=40 Ohms, X0=100 ohms
(1) Draw out the zero-, positive-, and negative- sequence reactance diagrams for the original system using a 100-MVA, 15-kV base. Neglect the ∆/Y transformer phase shift;
(2) For a fault with zero impedance at bus 1, determine the Thevenin equivalent circuit for each sequence network as viewed from faulted bus. Neglect the ∆/Y transformer phase shift and prefault voltage is 1 p.u. ;
(3) Determine the sub-transient fault current for the fault in (2).
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