Question

A single line diagram of a power system is shown in Fig. 2. The system data with equipment ratings and assumed sequence reactances are given the following table. The neutrals of the generator and A-Y transformers are solidly grounded. The motor neutral is grounded through a reactance Xn 0.05 per unit on the motor base. Assume that Pre-fault voltage is takin as VF-1.0 ,0° per unit and Pre- fault load current and Δ-Y transformer phase shift are neglected In the table below, X/ represents positive sequence reactance, X2 represents negative sequence reactance and, Xo represents zero sequence reactance of that device, and pu shows per unit value. (Some book uses Xt, X-, and X0 symbols for these sequences reactances) X-Xd j0.15 pu, X17 pu, X-j0.05 pu XXj0.20 pu, X-j0.21 pu, Xo-j0.10 pu, X j0.05 pu Generator G 100 MVA 13.8 kV Motor MM 100 MVA 13.8 kV Transformer T 100 MVA 13.8 kV/138 k Xi -X2-XiXo j0.10 pu Transformer T2 100 MVA 138 kV/13.8 k Xi -X2-XX j0.10 pu Transmission Line 138 kV X,-X 2-J0.105 pu, and X,-j0.3 I 5 pu a) A three-phase to ground fault occurs at the generator terminal (bus 1) through a fault impedance of Zr j0.08 per unit. Compute the fault current in per unit (be careful this is a balanced fault. 10 pts] b) A bolted (which means Zf0.0 p single line-to-ground short circuit occurs from phase a to ground at bus 1 (at the same bus with the section "a") (i) Draw the per-unit zero-, positive-, and negative-sequence networks (ii)Reduce the sequence networks to their Thévenin equivalents, as viewed from the generator terminal (bus 1). (iii)Calculate the sequence currents and the subtransient fault current in per-unit and in kA (be careful this an unbalanced fault) us Bus uS us Z, Short circuits@bus 1 Z j0.08 pu for the section 'a' and Z j0.0 pu for the section 'b Figure. Sinle-line diagram of a simple four-bus power system

Answer 1

2 ×0% J 0.3isfv Χ-x1°.jo.10S) 138kv , 13. PoRitive Sequenu Networ k: 138 1,6 (N

。0-1156 pv Zres 1.0 Faut Curerd I-D b) Negative Seguen de Network:- JOIDS JO.)。 JO.lo jons 23e (Gois) IC o1t Jo.in5 +) 0-1 joa1) (J0.IS

Y 0.315 0.3iS Line jous jaio-jo.IS 끈tel, b) Thevenin' iv 2 刁2e 2 resaie 2 0e

3x E 3x 0 G.2229 P MUA 100418c KA x 13.8 -6. 2274 x 4,1836 (Actuel) Jf 2G.0SS KA →Sino A)' Networks are in Seng au Seume Cutrent ave a