ECX5332- POWER SYSTEMS II
ACADEMIC YEAR: 2015/2016
Academic coordinator
: Dr. KAC Udayakumar
Course coordinator
: Dr. KAC Udayakumar
Contact Phone
: 011 -2881228 /011-2881351
E-mail
kauda@ou.ac.lk
ASSIGNEMNT 1
Due date: 26.02.2016
Answer all the questions
Question 1
a) Explain terms “steady-state stability”, “dynamic stability” and “transient stability”
of a power system. Give example for each.
b) What is “excitation system” of a generator?
c) The reactance of generator may be “synchronous”, “transient” or “sub-transient”.
State under which condition these reactances are used to model the generator.
What reactance is used for transient stability analysis? Give reasons
d) Explain why the transient stability limit is lower than steady-state stability limit
e) What do you understand by “infinite bus”
f) What are the methods of improving transient stability limit
g) Certain power plant consists of two generating units and both units are operating
in parallel
Unit 1: 200 MVA, 20 kV, 3000 rpm, H=4.65 s
Unit 2: 600 MVA, 22 kV, 1500 rpm, H=3.67 s
Determine:
i.
Kinetic energy stored in each machine
ii.
Inertia (M) constant of each machine
iii.
Equivalent H constant for two units on a 100 MVA base
Question 2
Certain three-phase, 50 Hz generator delivers 0.5 p.u. power to an infinite bus via a
transmission line (shown in figure Q2). Voltage at both ends of the lines are
maintained at 1 p.u. Reactance of the line is 0.42 p.u and resistance of the line is
neglected. Sub –transient reactance and inertia constant of the generator are 1.3
p.u. and 4 respectively.
1
X=j0.42
G
Infinite bus
P=0.5 p.u.
X’d=j1.3 p.u
H=4 s
Figure Q2
i.
ii.
iii.
iv.
v.
Calculate the excitation voltage of the generator.
Write the power angle equation for the steady state condition
What is the initial power angle?
Calculate the maximum power that can be delivered from generator to the
system
The circuit breakers of the line is open at t=0 and reclose when t= T. If the
generator does not lose the synchronism, what is the maximum possible
value for T?
Question 3
(a) Define the term “surge impedance loading”.
(b) Prove that when the loss less line delivers load equal to the surge impedance
loading voltages at both ends of the line are equal in magnitude.
(c) A 400 kV, 50 Hz, 300 km transmission line delivers 700 MW at 0.85 power factor
lagging. Parameters of the line are given below;
Series impedance : z=(0.025+j0.3) Ω/km
Shunt admittance : y=(j4x10-6) S/km
i.
ii.
iii.
If the voltage at the receiving end equals to the rated value determine the
sending end voltage current and power factor
Determine voltage, current and reactive power at the following points of the
line (distance is given from the receiving end of the line):
a) 75 m
b) 150 m
c) 225 m
State what would happen to the receiving end voltage when the load is
disconnected. Explain your answer.
2