A Solved problem to draw the per unit Reactance Diagram

Draw the per unit reactance diagram for the power systems shown below. Neglect resistance and use a base of 100MVA, 220KV in 50 ohms line. The ratings of the generator, motor and transformers are

dia

G: 40 MVA, 25 KV, X’’ = 20%; M: 50 MVA, 11 KV, X’’ = 30%

T1:40 MVA, 33 Y / 220 Y KV, X = 15%; T2: 30 MVA, 11 Δ /220Y KV, X = 15%

Load: 11 KV, 50MW + j68 MVAR

Solution:

Base MVAb new = 100 MVA; Base KVb new = 220 KV

Transmission line j50 Ω:

Zactual = j50 Ω

clip_image003

clip_image005

Transformer T1:

KVb old = 220 KV

clip_image007

clip_image009

Generator G1:

clip_image011

Transformer T2:

KVb old = 220 KV (HT side voltage)

clip_image013

clip_image015

Synchronous motor:

clip_image017

Reactance diagram:

clip_image019