Question

Q7. Two generators rated at 10 MVA, 13.2 kV and 15 MVA, 13.2 kV are connected in parallel to
a bus-bar. They feed supply to two motors of inputs 8 MVA and 12 MVA respectively. The
operating voltage of motors is 12.5 kV. Assuming base quantities as 50 MVA and 13.8 kV
draw the reactance diagram. The per cent reactance for generators is 15% and that for motors
is 20%​

Answer 1

Answer:

The one line diagram with the data is obtained as shown in figure P1(a).

Selection of base quantities: 50 MVA, 13.8 KV (Given)

 

Calculation of pu values:

XG1 = j 0.15 (50/10) (13.2/13.8)2 = j 0.6862 pu.

XG2 = j 0.15 (50/15) (13.2/13.8)2 = j 0.4574 pu.

Xm1 = j 0.2 (50/8) (12.5/13.8)2 = j 1.0256 pu.

Xm2 = j 0.2 (50/12) (12.5/13.8)2 = j 0.6837 pu.

 

Eg1 = Eg2 = (13.2/13.8) = 0.9565 ∠00 pu

 

Em1 = Em2 = (12.5/13.8) = 0.9058 ∠00 pu

 

Thus the pu reactance diagram can be drawn as shown in figure P1(b).

Explanation: