EEX5832 -Power Systems II
Assignment No 2 (2017/2018i)
Introduction: Objective of this assignment is to obtain necessary skills of load flow calculation
in power systems by the students. It is believed that the students have read the respective
sessions of the course material before attempting the assignment.
Students are allowed use excel worksheets for the calculations within iterations (parts II and III).
However, the calculation of the first iteration should be presented with necessary steps. At the
end of each iteration (parts II and III) the results should be presented in a form of a table
Penalty marks will be given for untidy answers.
Question
Single line diagram of a 100 MVA, 220 kV base power system is shown in figure Q1. Bus data
and line data of the system are given in tables 1 and 2. Bus 1 is considered as slack bus and the
voltage is maintained at 1.0 ∠00 p.u. Magnitude of the voltage at bus 2 is 1.02 p.u.
Bus 1
L1
Bus 3
L2
Bus 2
L3
Figure Q1
Table 1: Bus data
Bus No
P load
MW
1
-2
20
3
200
Q load
MVAr
-5
50
P gen
MW
-100
0
1
Q gen
MVAr
---0
Table 2: Line data
Line
L1
L2
L3
R (Ω)
5
4
4
XΩ
j40
j30
j50
Part I
a. Draw impedance diagram of the system
b. Form bus admittance matrix for the system
[15 marks]
Part II
Calculate voltage at buses using Gauss-Seidel method. Accuracy of the results should
be less than 0.1 p.u (ε<=0.1 p.u.)
[25 marks]
Part III
Calculate voltage at buses using Newton-Raphson method. Power mismatch should be
less than 0.1 p.u. (you may use formula given in moodle class (http://elearn.ou.ac.lk
) for Jakobian matrix element calculation)
[25 marks]
Part VI
a. Based on the results obtained in parts II and III, give your comments on above two
methods of load flow calculations with reference to number of iterations, calculation time
per iteration, convergence.
b. Calculate power flow through the lines using the results obtained in part II or part III (if
the last digit of your registration number is even – use results of part II, if the last digit of
your registration number is odd – use the results of part III)
c. Sketch the power flow diagram
d. Calculate slack bus power and power factor
e. Calculate total loss of the system and express as a percentage
f. Suppose reactive power of the generator at bus 2 obtained (in part II or III) is beyond the
actual reactive power limit of the generator at bus 2, explain how you proceed with the
calculation (no calculation is required)
g. Perform one iteration of “decoupled load flow calculation” and compare the results with
the results obtained in part II and III
[35 marks]
2