In developing per-unit circuits of systems such as the one shown in Figure 3.10, when moving across a transformer, the voltage base is changed in proportion to the transformer voltage ratings.

(a) True

(b) False

Figure 3.10

V, 220/0 volts Zone 1 Vspu 0.9167/0 p.u. = Zbase 38 T 30 kVA 240/480 volts Xeq = 0.10 p.u. Zone 1 Voaset 240 volts (240) 30,000 Spase = Ispu XT1p.u. = 1.92 30 KVA Zone 2 Xin = 21 (a) Single-phase circuit jXlinep.u. 10.10 p.u. 10.2604 p.u. Zbase2 Zone 2 Vbase2= 480 volts T 20 kVA 460/115 volts Xea = 0.10 p.u. = (480) 30,000 = 7.68 (b) Per-unit circuit Zload 0.9 + 10.2 jXT2p.u. hoadp.u. /0.1378 p.u. = Zbase3 Zone 3 base3 = Zone 3 Vbase3= 120 volts Zloadp.u. 1.875 +/0.4167 p.u. (120) 30,000 30,000 120 0.48 250 A