1. International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 –
6545(Print), ISSN 0976 – 6553(Online) Volume 4, Issue 4, July-August (2013), © IAEME
118
THE INFLUENCE OF OPTIMUM GENERATION ON TRANSIENT
STABILITY
Sameer S. Mustafa1
Mohammad A. Abdullah2
Bilal A. Nasir3
1
(Corresponding author, Kirkuk Technical College, Iraq)
2
(Mosul College of Engineering, University of mosul, Iraq)
3
(Hawija Technical Institute, Iraq)
ABSTRACT
Iraqi National Super Grid contains six generation sets (Baiji, Sad Al-Mosul, Haditha,
Mussayab, Nasiriya and Hartha), 27 transmission lines and 19 bus bars. The effect of optimum
generation on transient stability was studied using a programmable package build under Matlab in
case of different faults like: single line fault, two lines, line with generating plant fault…….etc.
Iraqi national control centre load and generation data was used. Three generating plants were
chosen to notice transient stability improvement in case of optimum generation.
Keywords: Optimum generation, Transient stability, Power system.
1. INTRODUCTION
Transient stability analysis has recently become a major issue in the operation of power
systems due to the increasing stress on power system networks. This problem requires evaluation of
a power system's ability to withstand disturbances while maintaining quality of service. Many
different techniques have been proposed for transient stability analysis in power systems, specially
for a multi-machine system. These methods include the time domain solutions, the extended equal
area criteria, and the direct stability methods such as the transient energy function. However, most
of the methods must transform from a multi-machine system to an equivalent machine and infinite
bus system. Power system stability may be defined as the property of the system, which enables its
synchronous machines to respond to a disturbance from a normal operating condition and return to
a condition where their operation is again normal [1], [2],[3].
Stability studies are usually classified into three types depending upon the nature and order of
disturbance magnitude. These are:
1. Steady-state stability.
2. Transient stability.
3. Dynamic stability.
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2. International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 –
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Transient stability studies aim to determine if the system remains in synchronism following
major disturbances such as:
1- Transmission system faults.
2- Sudden or sustained load changes.
3- Loss of generating units.
4- Line switching [4], [5].
Transient stability problems can be subdivided into first swing and multi-swing stability
problems. In first swing stability, usually the time period under study is the first second following a
system fault. If the machines of the system are found to remain in synchronism within the first
second, the system is said to be stable.
Multi-swing stability problems extend over a longer study period. In all stability studies, the
objective is to determine whether or not the rotors of the machines being perturbed return to
constant speed operation.
A transient stability analysis is performed by combining a solution of the algebraic equations
describing the network with a numerical solution of the differential equations describing the
operation of the synchronous machines. The solution of the network equations retains the identity of
the system and thereby provides access to system voltages and currents during the transient period.
The modified Euler and Runge-Kutta methods have been applied to the solution of the differential
equations in transient stability studies.
Iraqi National Super Grid network consists of 19 busbars and 27 transmission lines; the total
length of the lines is 3711 km., six generating stations are connected to the grid. They are of various
types of generating units, thermal and hydro turbine kinds, with different capabilities of MW and
MVAR generation and absorption. Figure1 and Table1 show the single line diagram and the names
of power plants of Iraqi (400) kV system [6], [7], [8].
Fig. 1. Configuration of the 400 kV Network

3. International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 –
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TABLE1: THE NAMES OF IRAQ NATIONAL SUPER GRID STATIONS
Bus barBus bar nameBus barBus bar name
KAZKhour-Al-ZubairBABBabel
KDSKadissiaBAJBaji
KRKKirkukBGEBaghdad East
KUTKUTBGNBaghdad North
MOSMosulBGSBaghdad South
MSBMussayabBGWBaghdad West
NASNasiriyaBQBBaquba
QAMQaimHADHaditha
QRNQurnaHADHaditha
SDMSad Al-MosulHRTHartha
2. TRANSIENT STABILITY CALCULATIONS
A software package under Matlab [9], is capable of performing load flow and transient
stability analysis of electric power systems. Load flow analysis is performed by means of Newton-
Raphson method. The Transient Stability calculations were carried out using the step by step
modified Euler iterative solution of the differential equations describing machines behavior of
INSG system. The software package is developed to perform minimum power losses based optimal
power flow analysis using Gradient method.
The solution to the stability took into account a time step of 0.05 second and total solution
time period of 1.5 second. The program performs transient calculations with different types of faults
at any point on the system with 0.15 second clearing time (tc). Rotor angles were taken as an
indicator of transient stability.
3. TRANSIENT STABILITY CASE STUDIES
Generating values as shown in Table2 was chosen as ordinary generation [7]. The optimum
values of generation were calculated using the modified programmable package. The values for
both ordinary and optimum generation were tabulated in Table3.

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TABLE 2: THE LOAD & GENERATION
TABLE 3: ORDINARY & OPTIMUM GENERATION OF THE NATIONAL SUPER GRID
A: Three Phase Fault in the Middle of Line (BAJ-KRK)
Although the system is stable in case of three phase fault in the middle of line (BAJ-KRK)
with ordinary load flow, the system becomes more stable with OPF.
Swing curves of SDM, HAD and NSR power plants which represent their stability as shown
in Figs. 2,4 and 6 respectively were improved when OPF were implemented as shown in Figs.3,5
and 7. The improvement in transient stability is the difference between the change in rotor angles
for ordinary condition and the change in rotor angles for optimum conditions, divided by the change
during ordinary condition [6].
Bus
Bar
No.
Bus Bar
Name
Generation Load
MW MVAR MW MVAR
1 BAJ 570.592 100.4455 200.00 98.00
2 SDM 700.00 - 23.2248 5.00 2.00
3 HAD 500.00 - 0.8474 100.00 60.00
4 QAM .00 .00 60.00 40.00
5 MOS .00 .00 300.00 180.00
6 KRK .00 .00 70.00 40.00
7 BQB .00 .00 150.00 80.00
8 BGW .00 .00 500.00 360.00
9 BGE .00 .00 500.00 360.00
10 BGS .00 .00 100.00 50.00
11 BGN .00 .00 300.00 200.00
12 MSB 600.00 420.6564 120.00 70.00
13 BAB .00 .00 100.00 50.00
14 KUT .00 .00 100.00 60.00
15 KDS .00 .00 200.00 100.00
16 NAS 650.00 - 69.1434 100.00 54.00
17 KAZ .00 .00 350.00 200.00
18 HRT 380.00 35.9855 38.00 22.00
19 QRN .00 .00 70.00 30.00
Total 3400.592 463.8716 3363 2056
Generation
Bus Name
Optimum
Generation
[Mw]
Ordinary
generation
[Mw]
BAJ 240.592 570.592
SDM 257 700
HAD 343 500
MSB 985 600
NSR 506 650
HRT 409 380

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For SDM power plant the change in rotor angle = 21-12.6 = 8.4 degree in case of ordinary
condition as shown in Fig.2. The change is equal to 12.5 – 5.5 = 7 degree during optimum condition
as shown in Fig.3
So the improvement in transient stability for SDM according to the amplitudes of swing
curves is equal to:
(( 21-12.6) – (12.5-5.5)) / (21-12.6) x100% = 16.6%
Using the same procedure and as shown in figures 4&5 stability improvement for HAD
power plant is equal to: (( 14.5-2) – (9.6-11.6 )) / (14.5-2 ) x 100% = 84%
Also stability improvement for NSR power plant as shown in Figures 6&7 is equal to:
((9.5- (-9.5) –(8-4.7)) / ((9.5-(-9.5)) x100%=82.5%
Fig. 2. Swing curve for (SDM) generating machine for fault in the middle of line(BAJ-KRK)
with ordinary load flow
Fig. 3. Swing curve for (SDM) generating machine for fault in the middle of line(BAJ-KRK)
with optimum power flow
0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6
4
6
8
10
12
14
16
18
20
22
Rotor Angle in degree for gen. SDM4
Time[sec]
0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6
10
15
20
25
30
35
Rotor Angle in degree for gen. SDM4
Time[sec]

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Fig. 4. Swing curve for (HAD) generating machine for in the middle of line(BAJ-KRK) with
ordinary load flow
Fig. 5. Swing curve for (HAD) generating machine for fault in the middle of line(BAJ-KRK)
with optimum power flow
Fig. 6. Swing curve for (NSR) generating machine for fault in the middle of line (BAJ-KRK)
with ordinary load flow
0 0.5 1 1.5
6
8
10
12
14
16
18
20
Rotor Angle in degree for gen. HAD4
Time[sec]
0 0.5 1 1.5
-10
-5
0
5
10
15
Rotor Angle in degree for gen. NSR4
Time[sec]
0 0.5 1 1.5
0
5
10
15
20
25
Rotor Angle in degree for gen. HAD4
Time[sec]

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Fig. 7. Swing curve for (NSR) generating machine for fault in the middle of line (BAJ-
KRK) with optimum power flow
B: Three Phase Fault in the Middle of Line (HAD-QAM)
Using the same procedure as in case study A, stability improvement for SDM plant is equal
to 97.4% as shown in Figs.8 and 9. Also Figures 10,11 and 12,13 show the behavior of HAD and
NSR generating machines with stability improvement equal to, 67.9% and 50.8% respectively.
Fig. 8. Swing curve for (SDM) generating machine for fault in the middle of line(HAD-QAM)
with ordinary load flow
0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6
10
15
20
25
30
35
40
45
50
Rotor Angle in degree for gen. SDM4
Time[sec]
mid 3-4 fault(mod)
0 0.5 1 1.5
0
5
10
15
20
25
Rotor Angle in degree for gen. HAD4
Time[sec]

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Fig. 9. Swing curve for (SDM) generating machine for fault in the middle of line (HAD-QAM)
with optimum power flow
Fig. 10. Swing curve for (HAD) generating machine for fault in the middle of line(HAD-
QAM) with ordinary load flow
0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6
5
10
15
20
25
30
Rotor Angle in degree for gen. SDM4
Time[sec]
mid 3-4 fault(mod)
0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6
-20
-15
-10
-5
0
5
10
15
20
25
Rotor Angle in degree for gen. HAD4
Time[sec]
mid 3-4 fault(mod)

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Fig. 11. Swing curve for (HAD) generating machine for fault in the middle of line(HAD-
QAM) with OPF
Fig. 12. Swing curve for (NSR) generating machine for fault in the middle of line(HAD-QAM)
with ordinary load flow
0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6
0
2
4
6
8
10
12
14
16
18
Rotor Angle in degree for gen. HAD4
Time[sec]
mid 3-4 fault(mod)
0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6
-30
-25
-20
-15
-10
-5
0
5
10
15
Rotor Angle in degree for gen. NSR4
Time[sec]
mid 3-4 fault(mod)

10. International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 –
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Fig. 13. Swing curve for (NSR) generating machine for fault in the middle of line (HAD-QAM)
with optimum power flow
4. CONCLUSION
According to the swing curves (Figures 2 – 13) of the generating machines for Iraqi National
Super Grid for different faults, we conclude that: Transient stability could be improved if generating
plants gave optimum generating values. Comparison between stability with OPF and stability with
ordinary power flow according to the rotor time angle curves indicates that the stability is much
better with OPF.
REFERENCES
[1] Stevenson W. D., Elements of Power System Analysis, McGraw-Hill Book co. 4th edition,
1985
[2] Kim S.(2001), “Generation Redispatch Model to Enhance Voltage Security in Competitive
Power Market using Stability Constrained Optimal Power Flow", Available: http://
www.ee.server, Korea. Ac. Kr.
[3] Ray D. Zimmerman, “A Transient Stability Constrained Optimal Power Flow”, Bulk Power
System Dynamics and Control IV-Restructing, August 24-28, Santorini Greece, 2000.
[4] Yue Yuan, “A study of Transient Stability Constrained Optimal Power Flow with Multi-
Contingency”, T.IEE Japan, Vol. 122-B, No. 7, 2002, Japan
[5] Al-Sammak A. Nasser, "A New Method for Transient Study with Application to INRG",
M. Sc. thesis, University of Mosul, Electrical Engineering Department, 1999, Mosul.
[6] Afaneen A. Abood," Automated Mapping Facilities Management Geographic Information
System of a Power System", M. Sc. Thesis, University of Technology, Baghdad, 1998.
0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6
-8
-6
-4
-2
0
2
4
6
8
10
Rotor Angle in degree for gen. NSR4
Time[sec]
mid 3-4 fault(mod)

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[7] Afaneen A. Abood," Implementation of Geographic Information System (GIS) in Real-Time
Transient Stability", Ph.D. thesis, University of Technology, Baghdad, 2004.
[8] Samir S. Mustafa, "Minimum Power Losses Based Optimal Power Flow Iraqi National
Super Grid and its Effect on Transient Stability", Ph.D thesis, University of Technology,
Baghdad, 2007.
[9] Al Azawi Faiq et al., “Power System Analysis Programs”, Al Nahreen University, August
2001.
[10] Dharmendra Kumar Singh, Dr.Moushmi Kar and Dr.A.S.Zadgaonkar, “Analysis of
Generated Harmonics Due to Transformer Load on Power System using Artificial Neural
Network”, International Journal of Electrical Engineering & Technology (IJEET),
Volume 4, Issue 1, 2013, pp. 81 - 90, ISSN Print : 0976-6545, ISSN Online: 0976-6553.
[11] Preethi Thekkath and Dr. G. Gurusamy, “Effect of Power Quality on Stand by Power
Systems”, International Journal of Electrical Engineering & Technology (IJEET), Volume 1,
Issue 1, 2010, pp. 118 - 126, ISSN Print : 0976-6545, ISSN Online: 0976-6553.
[12] D. Pattanayaka, M. Basub and R. N. Chakrabartic, “Multi-Objective Differential Evolution
for Optimal Power Flow”, International Journal of Electrical Engineering & Technology
(IJEET), Volume 3, Issue 1, 2012, pp. 31 - 43, ISSN Print : 0976-6545, ISSN Online:
0976-6553.
[13] Mohd Abdul Lateef, Syed Maqdoom Ali and Dr.Sardar Ali, “Reactive Power Aspects in
Reliability Assessment of Power Systems”, International Journal of Advanced Research in
Engineering & Technology (IJARET), Volume 4, Issue 3, 2013, pp. 124 - 131, ISSN Print:
0976-6480, ISSN Online: 0976-6499,