Sequence networks

1. Unit III Practice Questions
Q1. Draw the positive, negative and zero sequence impedance networks for the power system given in the figure.
Choose a base of 50 MVA, 220kV in the 100 ohms transmission line and mark all impedances in pu. The
ratings of the generators and transformers are:
Generator 1: 25 MVA, 11kV, X1=20%; X2=20%;
Generator 2: 25 MVA, 11kV, X1=20%; X2=20%;
Three-phase transformer (each): 20MVA, 11 Y/220 Y kV, X=15%. The zero sequence reactance of each
machine is 8%. The neutral reactance is 5% on individual machine ratings.
Q2. Draw the positive, negative and zero sequence impedance networks for the power system given in
the figure. Choose a base of 50 MVA, 220kV in the 50Ω transmission lines and mark all impedances
in pu. The ratings of the generators and transformers are:
Generator 1: 25 MVA, 11kV, X1=X2=20%, Xg0 = 10%
Generator 2: 25 MVA, 11kV, X1=X2=15%, Xg0 = 8%
Three-phase transformer (each): 20MVA, 11 Y/220 Y kV, X=15%
The zero sequence reactance of each machine is 8%. Assume that the zero sequence reactance
of the lines is 250% of their positive sequence reactance.

2. Q3. Draw the positive, negative and zero sequence impedance networks for the power system given in
the figure. Choose a base of 100 MVA, 200kV in the 100 ohms transmission line and mark all
impedances in pu. The ratings of the generators, transformers are:
G1: 20 MVA, 11kV, X1=20%; X2=10%; G2: 50 MVA, 33kV, X1=20%; X2=15%;
YY Transformer: 50MVA, 200/11KV, X= 10%; Y∆ Transformer: 45MVA, 200/33KV, X = 15%.
The zero sequence reactance of each machine is 5%.
The neutral reactance is 3% on individual machine ratings.
Q4. Draw all the sequence networks for the power system shown in the figure below:
Choose a base of 50 MVA, 220KV in the 50 ohm transmission lines and mark all the reactances in
pu. The ratings of the generators and the transformers are:
Generator 1 : 25MVA, 11KV, X1=X2=15%, Xg0 = 5%
Generator 2 : 25MVA, 11KV, X1=X2=10%, Xg0 = 8%
3 phase transformers(each) = 20 MVA, 11 /220 KV, X = 15%
The negative sequence reactance of each synchronous machine is equal to its positive seq.
reactance. The zero sequence reactance of each machine is 8%. The neutral reactance is 5%.

3. Q5. Draw the positive, negative and zero sequence impedance networks for the power system given in
the figure. Choose a base of 150 MVA, 220kV in the 60 ohms transmission line and mark all
impedances in pu. The ratings of the generators, transformers are:
G1: 50 MVA, 13kV, X1=25%; X2=15%; G2: 40 MVA, 25kV, X 1=15%; X2=10%;
YY Transformer: 45MVA, 220/15KV, X= 15%; Y∆ Transformer: 50MVA, 230/35KV, X = 10%.
The zero sequence reactance
of each machine is 4%.
The neutral reactance is 5%
on individual machine ratings.