1.0
INTRODUCTION
Power system consists some synchronous machines operating in synchronism. For the
continuity of the power system, it is necessary that they should maintain perfect synchronism under
all steady state conditions. When the disturbance occurs in the system, the system develops a force
due to which it becomes normal or stable. The ability of the power system to return to its normal
or stable conditions after being disturbed is called stability. Disturbances of the system may be of
various types like sudden changes of load, the sudden short circuit between line and ground, lineto-line fault, all three-line faults, switching, etc.
The stability of the system mainly depends on the behaviour of the synchronous machines
after a disturbance. The stability of the power system is mainly divided into two types depending
upon the magnitude of disturbances which is steady state stability and transient stability. Steady
state stability refers to the ability of the system to regain its synchronism (speed & frequency of
all the network are same) after slow and small disturbance which occurs due to gradual power
changes. Steady-state stability is subdivided into two types which is dynamic stability and static
stability.
Transient stability is defined as the ability of the power system to return to its normal
conditions after a large disturbance. The large disturbance occurs in the system due to the sudden
removal of the load, line switching operations; fault occurs in the system, sudden outage of a line,
etc. Transient stability is conducted when new transmitting and generating system are planned.
The swing equation describes the behaviour of the synchronous machine during transient
disturbances. The transient and steady-state disturbances occur in the power system are shown in
Figure 1.0. These disturbances reduce the synchronism of the machine, and the system becomes
unstable. Stability studies are helpful for the determination of critical clearing time of circuit
breakers, voltage levels and a transfer capability of the systems.
Figure 1.0: The transient and steady-state disturbances occur in the power system
2.0
OBJECTIVES
At the end of this laboratory session, we are able
1. To model a test system model of power system suing MATLAB Simulink.
2. To analyze the dynamic responses of the system following a disturbance.
3. To assess the rotor angle stability of the given system for different types of disturbance.
3.0
SCOPE
This task is limited to the following scope
1. The PSS analysis created by using MATLAB R2013B.
2. Simulate the dynamic responses of the system disturbance in the system.
3. Assess the rotor angles stability of each machine for the system.
4.0
LITERATURE REVIEW

Theory related in transient stability studies.
The stability of power system has been and continues to be major concern in system operation.
Modern electrical power system has grown to a large complexity due to increasing
interconnections. Installation of large generating unit sand extra high voltage tie lines etc.
transient stability is the ability of the power system to maintain synchronism when the subject to
a severe transient disturbance, such as a fault on transmission facilities, sudden loss of
generation, or loss of a large load. The system response to such disturbances involves large
excursions of generator rotor angle, power flows, bus voltage and other system variables. It is
important while steady state stability is function only on operating conditions, transient stability
is a function of both operating condition and the disturbances.
This complicates of transient stability considerably. Repeat analysis is required the different
disturbance that are considered. In the transient stability studies, frequently considered
disturbances are the short circuits of the different type. Normally the three phase short circuit at
the generator bus is the most severe type, it causes maximum acceleration of the connected
machine.
A system is configured in term of block diagram representation from a library of standard
component. A system is block diagram representation is built easily and the simulation results
are displayed quickly. Simulation algorithms and parameters can be changed in the middle of a
simulation with intuitive results, thus providing the user with a ready access learning tool for
simulating many of the operational problem found in the real world. Simulink is particularly
useful for studying the effects od nonlinearity on the behavior of the system.

Transient Stability.
Transient state stability is the ability of the power system to maintain in stability after large oe
sudden disturbances. For the example, occurrence of faults, sudden load changes and line
switching. These include severe lighting strike, loss of transmission line carrying bulk power due
to overload. Transient stability studies involving the determination of whether or not
synchronism is maintained after the machine has been subjected to severe disturbance.
Any disturbance in the system will cause the imbalance between the mechanical power input to
the generator and electrical power output of the generator to be affected. As a results, some of
the generators will tend to speed up and some will slow down. For the particular generator, the
tendency is to big, it will no longer remain in synchronism with the rest of the system and will be
automatically disconnected from the system.
5.0
METHODOLOGY
6.0
ANALYSIS AND DISCUSSION
After the details of parameter is setup as provided using Simulink Matlab, the system is simulated,
and the graph is plotted referred to rotor angles, rotor speeds, electrical power of each machine to
unstable case
Task 1: Sudden large increment of load at Bus 7
i.
Normal condition
Based on the figure shows the rotor angle, rotor speed and generator electrical power at the
normal condition. Where the angle and the speed are stable through the period of time.
ii.
Large increment condition
Based on the figure shows the rotor angle, rotor speed and generator electrical power is
increase to 50% of load. Where the angle is stable through the period of time but the speed of the
rotor was decrease toward zero because of large increases of load.
Task 2: Large increment of load at Bus 7
i.
Normal condition
Based on the figure shows the rotor angle, rotor speed and generator electrical power at the
normal condition. Where the angle and the speed are stable through the period of time. The
clearing time is 20second, switching time is 1 -2second. The power isin normal condition with is
967MW.
ii.
Large increment condition.
Based on the figure shows the rotor angle, rotor speed and generator electrical power is
decrease to 50% of load with is 483.5MW. Where the angle and the speed of rotor are unstable. The
clearing time is 20second and the switching time is 1-2ssecond.
Task 3: Large increment of load at Bus 9
i.
Normal condition
Based on the figure shows the rotor angle, rotor speed and generator electrical power at the
normal condition. Where the angle and the speed are stable through the period of time.
ii.
Large increment condition
Based on the figure shows the rotor angle, rotor speed and generator electrical power is
increase to 10% of load. Where the angle and the speed of rotor are unstable.
Task 4: Large decrement of load at Bus 9
i.
Normal condition
Based on the figure shows the rotor angle, rotor speed and generator electrical power at the
normal condition. Where the angle and the speed are stable through the period of time. The
clearing time is 20second, switching time is 1 -2second. The power is decrease to 45% with is
971.85MW.
ii.
Large decrement condition
Based on the figure shows the rotor angle, rotor speed and generator electrical power is not
decrease with is 1767MW. Where the angle and the speed of rotor are unstable. The clearing time
is 20second and the switching time is 1-2second.
Task 5: Temporary bolted three-phase fault at bus 8
1st Condition: Stable
Cleareance time (tc): 0.40s – 0.41s
Figure: rotor angles at bus 8 for 1st condition
Figure: rotor speeds at bus 8 for 1st condition
Figure: generator electrical power at bus 8 for 1st condition
Based on the figure shows the rotor angle, rotor speed and generator electrical power at
the stable condition where the clearing time is 0.40s – 0.41s. All the peak of the generator is
positive. The peak of the generator 1 is 29° while the generator 2 peak’s is 18°. The peak for
generator 3 and 4 is 21° and 30°. After the fault occurred at the generator, the generator will
settle down to new equilibrium point until the system transiently stable when the time is 10
second.
2nd Condition: Critically Stable
Clearance time (tc): 0.86s – 0.87s
Figure: rotor angles at bus 8 for 2nd condition
Figure: rotor speeds at bus 8 for 2nd condition
Figure: generator electrical power at bus 8 for 2nd condition
Based on the figure shows the rotor angle, rotor speed and generator electrical power at
the clearing time is 0.86s – 0.87s. The peak of the generator 1 is 70° while the generator 2 peaks’
is 65°. The peak for generator 3 and 4 is 65° and 78°. It shows that the rotor angle is critically
stable and each generator gives 4 differences reading. The system almost unstable when the fault
occurred. The stable of the system is in final stage before it will be unstable. The precaution step
must be taken to ensure the system from breakdown.
3rd Condition: Unstable
Clearance time (tc): 0.87s – 0.88s
Figure: rotor angles at bus 8 for 3rd condition
Based on the figure shows the rotor angle, rotor speed and generator electrical power at
the clearing time is 0.87s – 0.88s. The generator 1 and 2 is the same unstable state where it is
temporary near to zero value and increasing linearly to positive value until it stop and reach
maximum point or time. The generator 3 and 4 is the same unstable state where it is temporary
near to zero value and increasing linearly to negative value until it stop and reach maximum
point or time. The generator will not settle down to the equilibrium point because of the system
is completely unstable.
Task 7: Temporary bolted three-phase fault at bus 5
Condition: Unstable only
Clearance time (tc): 0.40s – 0.41s
Figure: rotor angles at bus 5
Figure: rotor speeds at bus 5
Figure: generator electrical power at bus 5
Task 8: Temporary bolted three-phase fault at bus 11
Condition: Unstable only
Clearance time (tc): 0.40s – 0.41s
Figure: rotor angles at bus 11
Figure: rotor speeds at bus 11
Based on the figure shows the rotor angle, rotor speed and generator electrical power at
the clearing time is 0.40s – 0.41s at bus 11. The generator 3 and 4 is the same unstable state
where it is decreasing linearly to negative value until it will stop and reach maximum point or
time. The generator will not settle down to the equilibrium point because of the system is
completely unstable. The fault occurred in short period of time because of small distance in
transmission line. It will not reach generator 1 and 2 because of the fault occurred in area 2. So
the generator 1 and 2 is not necessary
7.0
CONCLUSION
In conclusion, the power system stability analysis had been success, With the help of MATLAB
R2013B, the model of the system had been created according to our task which is to assess the
rotor angles stability of each machine for the system. The type of fault parameter was used to alter
is already prepared so that the program simulates exactly as the task had been given. The plot
diagrams can be of reference to determine the function of power system stability in a model of
power system. This experiment will surely help us as fellow engineers to gain knowledge about
power system analysis in real life situation.
8.0
REFERENCES
P.Kundur, Power system Stability and control, EPRI Power Sytem Engineering Series.
Louis-A Dessaint et al., ‘Power system simulation tool based on Simulink, IEEE Trans. Industrial
Electronica 1999, 1252-1254
P.M Anderson and A.A.Fouad, Power System Control and stability 1977
M. Klein, G.J.Rogers,P Kundur,”A fundamental Study of Inter –Area Oscillation in Power
Systems,”IEEE Transsactions on Power System.vol 6, No 3,August 1991