480 Vbase2 (240) = 480 = 480 volts 240 115 Vbase3 (480) 120 volts 460 V base2 4802 7.68 Ω Zbase2 Sbase 30,000 Zbase3 V base 3 Sbase 1202 30,000 0.48 Ω Sbase 30,000 = 250 A Ibase3 Vbase3 120 460 30,000\ XT2p.u. (0.10) = 480 20,000 = 0.1378 per unit 115 30,000\ XT2p.u. = (0.10) = 0.1378 per unit 120 20,000 2 line Xlinep.u. 0.2604 per unit Zbase2 7.68 Zloadp.u. Zload Zbase3 0.9 + j0.2 0.48 1.875j0.4167 per unit Iloadp.u. = Isp.u. sp.u. j(XT1p.u. +Xlinep.u. + XT2p.u.) + Zloadp.u. 0.9167/0° j(0.10+ 0.2604+0.1378) + (1.875 + j0.4167) 0.9167/0° 0.9167/0° 2.086/26.01° 1.875+j0.9149 = 0.4395-26.01° per unit Iload = (loadp.u.) I base3 = (0.4395/-26.01°) (250) = 109.9/-26.01° A Zone 1 V₁ = 220/0° volts V spu = 0.9167/0° p.u. Zone 2 Zone 3 38 T₁ 30 kVA 240/480 volts Xea = 0.10 p.u. Xune 20 I www T₂ Zload = 0.9 +0.2 20 KVA 460/115 volts Xea = 0.10 p.u. (a) Single-phase circuit ¡XT2p.u hoadou. Isp. u. jXTID.U. Хипери j0.10 p.u. j0.2604 p.u. I p.u. /0.1378 Zoadou = 1.875j0.4167 p.u. Zone 1 V base1 = 240 volts Zone 2 Vbase2 == 480 volts Zone 3 Vbase3 120 volts Zbase1 = (240)² 30,000 1.92 Zbase2 (480)2 30,000 (120)2 = 7.68 Zbase3 = = 0.48 30,000 Spase = 30 kVA 30,000 Ibase3 = = 250 A 120 (b) Per-unit circuit Zp.u. new = Zp.u.old V baseold V basenew Sbasenew (3.3.11) Sbaseold