Question

A 100 MVA, 12 kV Single-phase generator has a sub transient reactance of 20%. The generator supplies a two synchronous motors over 25-km transmission line having transformers at both ends. The motors, all rated 6.0 kV, 66 MVA and 50 MVA for Mi and M2, respectively. For both motors X" = 15%. The single phase transformer T is rated 150 MVA, 132/12 kV with leakage reactance of 12%. Transformer T2 is rated 132/6.6 kV, 40 MVA with leakage reactance of 10%. Series reactance of the transmission line is 0.4 2/km. Use the following base in the transmission line circuit: Sb=150MVA, and V8=150 KV Draw the impedance diagram, with all impedances marked in per-unit [20 points) Calculate the base current in the generator circuit [10 points) Calculate the actual value in Ohms for Transformer Ti reactance as seen from High voltage side [20 points]

note that
1) single phase system
2) base values at transmission line circuit

Answer 1

Solution - Given - Shit HU Generator : Ti Ty :: 400 MVA 12 kV , xd=20% Iso mra132/12 kV , **"=12% 40 MVA, 132/ 6.6 kV, Xtz 10 T.l. M My : : : 25km, 0.42/km = Xi GKV, 66 MVA , x my = 150% 6kV, 50 MVA ; * me = 15%. We are given base values of transmission line as Sp = 150 MYA, Viby = 150 kv. a l MVA new) x 1 Vold) xg (new) = xg (old) + ( + old Vnew = 0.2325 pu

As we know by transformer rule- 12 132 24 150 5 2 = 13.63 kv HOLO Telemarketingos X= 1363 X • Voltage base at generator side = 13.63 kv. Similarly, new voltage base on voltage base on motor side - q xs 7.5kV 132 ISO Hence new voltage base on motor side = 7.5kr. Now xey Cuev) = 0112 * (T) () = 0.0929 pu Rey Chaw) = 0.1 * (40) * ( 9 ) 2 Arnedo -0.290u pu We have reactance of Tol = 0.4elum 8 total reactance Xi = 0.4 x 25 km = 10 12

Koove of TL = : x (P.1) = - Leon = 150 x1 (actual) - or 0-0 4610 | 150 z base For motor, xm, (new) = 0.15* 1 = 0.218 pu Km2 (new) = 0.15X(1506956)* = 0 .289 pue fence reactance diagram - ca) 0.29 pu 0.2325 fu 0.0929 pu 0.0667pu mohon Xt2 xm, = 0.218 pu & Xm, & 0.288 pu ILO 1209 (b). Base cument from generator circuit - 9 Sbase (new) - 150 MVA 13.63 kV base (new) Ibase = 11KA

(c) for Transformer T, Vbase = 132 kV, Sbase = 150 MVA : : Zbost a = 132*116.168 . So, Actual value (2) = Zpu x base = 0.128 116.16 2 = 13.93 m. z 13.93 2