I J C T A, 8(5), 2015, pp. 2029-2036
© International Science Press
Application of Static Synchronous Series
Compensator (SSSC) to Enhance Power
Transfer Capability in IEEE Standard
Transmission System
Aswathi Krishna D.* and M.R. Sindhu**
Abstract: This paper presents implementation of Static Synchronous Compensator (SSSC) in an IEEE 5 bus system
for real and reactive power flow control, to meet constraints on bus voltage magnitude, stability and thermal limits.
This is made possible by appropriately controlling the magnitude and phase angle of injected voltage of series
compensator. Simulation results obtained after performance study of SSSC in MATLAB/SIMULINK validate the
effectiveness of the controller. The comparative study of the simulation results before and after compensation
shows reduction in losses, overloading and improvement in bus voltage profile attained with SSSC compensation.
Keywords: Static Synchronous Series Compensator, Real Power Flow Control, Reactive Compensation, Voltage
stability, FACTS.
1.
INTRODUCTION
The demand on power consumption is growing day by day due to modernization. Smooth and efficient
controllers were designed for the equipment in the system. The expansion or up gradation of the existing
system is not preferred from the economical point of view [1]. As an attempt to optimally utilize the
existing power system resources, Flexible AC Transmission System (FACTS) has been initiated [2]. Among
all the FACTS devices implemented, Static Synchronous Compensator (SSSC) is the best option for
controlling power flow by keeping the system stable and with minimum losses. SSSC can increase or
decrease power transferred and is capable of series compensation as well as voltage regulation [3].
Several cases of FACTS devices – such as SVC [2], STATCOM [2], TCSC [2], TSSC [2] etc were
studied in different system configurations. These show enhancement in power transfer capability, reduction
in power losses and maintenance of voltage stability. Operation of the system in different modes needs
separate control strategies [4]. Hence a unique control strategy for SSSC, to operate it under different
modes is required to meet the requirement of power system.
Many research works were published in steady state and dynamic modeling and control of SSSC. The
control methods discussed are traditional PI/PID control [4], Automatic Voltage Control [2], Quantitative
Feedback Theory (QFT) [5], Reactive Power Control [2], Adaptive Neuro Fuzzy Interference Controller
(ANFIC) [6], Direct Power Control [2] etc. Each controller technique has its own advantages as well as
disadvantages.
This paper presents results of SSSC implementation in IEEE standard system. The paper is organized
as follows:-Section 2 explains the specifications and characteristics of IEEE 5 bus system. Section 3 explains
*
Dept of Electrical and Electronics Engineering, Amrita School of Engineering, Coimbatore, Amrita Vishwa Vidyapeetham, Amrita
University, India, Email: achu.akd.92@gmail.com
**
Dept of Electrical and Electronics Engineering, Amrita School of Engineering, coimbatore, Amrita Vishwa Vidyapeetham, Amrita
University, India, Email: sindhumadassery@gmail.com
2030
Aswathi Krishna D. and M.R. Sindhu
in detail the control strategy of SSSC. Section 4 presents simulation results after the installation of SSSC in
the IEEE standard 5 bus system.
2. TEST SYSTEM
IEEE standard 5 bus system shown in Figure.1 is the selected test system. It consists of 2 generating plants,
3 load buses, 1 PV bus and 7 transmission lines [7]. Bus 1 is set as swing bus. Base kV and base MVA for
the system is selected as 100kV and 100 MVA respectively. Therefore base impedance and base current are
100Ù and 1000A respectively. Bus data, Transmission line parameters and load flow analysis results in
IEEE standard 5 bus system are shown in table 1 and 2.
Figure 1: IEEE 5 Bus System
Table 1
Bus data
Node
1
2
3
4
5
P (p.u)
(generated)
Q (p.u)
(generated)
P (p.u)
(demand)
Q(p.u)
(demand)
1.526
0.3
0
0
0
0.6584
-0.6512
0
0
0
0
0
0.45
0.80
0.50
0
0
0.20
0.30
0.25
Table 2
Transmission Line Parameters
Transmission Line
1-2
1-3
2-3
2-4
2-5
3-4
4-5
Impedance
(p.u)
Line Charging
(y/2)(p.u)
0.02+j0.06
0.08+.j0.24
0.06+j0.18
0.06+j0.18
0.04+j0.12
0.01+j0.03
0.08+j0.24
j0.03
j0.025
j0.020
j0.020
j0.015
j0.010
j0.025
Application of Static Synchronous Series Compensator (SSSC) to Enhance Power Transfer...
2031
Waveforms of each of the Bus voltages are shown in the figure 2.
From the above results, it is seen that the system attains steady state. Power generation and power
demand are balanced. Voltage angle difference between two neighboring buses exceeding 6� results in
overloading [8]. Hence from the results, line 2-4 is overloaded. SSSC is implemented to enhance power
transfer capability in line 2-4
3.
CONTROL STRATEGY OF SSSC
Load flow equations that regulate power system are:
Table 3
Power Flow in Transmission Lines
Node 1
Node 2
S12(p.u)
S21(p.u)
1
2
1.0087+0.5250i
–0.9846–0.5158i
1
3
0.5173+0.1333i
–0.4960–0.1210i
2
3
0.3376+0.0087i
–0.3307+0.0099i
2
4
0.4022+0.0149i
–0.3925+0.0049i
2
5
0.5448–0.1118i
–05326+0.1188i
3
4
0.3768–0.0691i
–0.3752+0.0545i
4
5
–0.0323–0.0727i
0.0326+0.0250i
Figure 2: Bus Voltages in IEEE 5 Bus System
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Aswathi Krishna D. and M.R. Sindhu
n
PGi � PDi � � | Vi || V j || Yij | cos(�ij � � i � � j ) � 0
j �i
(1)
n
QGi � QDi � � | Vi || V j || Yij | sin(�ij � � i � � j ) � 0
j �1
(2)
Where
PGi = Real power generation at i th bus.
PDi = Real power demand at i th bus.
QGi = Reactive power generation at bus.
QDi = reactive power demand at bus.
The load flow in the system should satisfy a set of constraints-constraints on real and reactive generator
power outputs, bus voltage magnitude constraints, constraints on tap setting transformers, capacitor bank
reactive power specifications, loading limit on transmission lines and voltage stability limits. The constraints
are mathematically represented as,
(1) Generator real and reactive power output constraints
PGi min � PGi � PGi max ; i � 1, 2,....N G
QGi min � QGi � QGi max ; i � 1, 2,....N G
(3)
(2) Voltage magnitude of each bus
min
max
| Vi |0.9
pu �| Vi |�| Vi |1.1 pu ; i � 1, 2,... N
(4)
Ti min � Ti � Ti max ; i � 1, 2....N
(5)
(3) Tap setting of transformers
(4) Capacitive bank reactive power output limits
QCi min � QC � QCi max ; i � 1, 2.....NC
(6)
(5) Loading on transmission line
Si � Si max ; i � 1, 2...N L
(7)
SSSC can improve the power transfer capability of transmission line 2-4. The control strategy should
also satisfy the limits on SSSC series injected voltage.
| Vse |min �| Vse |�| Vse |max
Qse min � Qse � Qse max
(8)
The overall control strategy of SSSC includes:
(1) A central controller generates bus voltage and real power flow reference values.
(2) SSSC controller to attain required settings of real power, reactive power and bus voltages keeping
thermal and voltage transmission constraints.
Application of Static Synchronous Series Compensator (SSSC) to Enhance Power Transfer...
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According to table 3, flow of real power and reactive power in transmission line without any compensation
is 0.4022p.u, 0.0149p.u respectively.
5.
REAL POWER CONTROL MODE
Since line 2-4 is overloaded, SSSC is installed to reduce the reactive power flow and real power through
the line. When SSSC is connected to the line, reactive and real power flow are reached to the limits 0.43pu
(430MW) and 0.154pu (154MW) respectively. The change in bus voltage magnitudes and phase angle can
be noted from plots shown below.
Above simulation results show that:
1. SSSC improves bus voltages in order to meet the desired power flow.
2. SSSC increases the real power flow through the transmission line 2 – 4 from 0.4022 p.u to 0.43 p.u.
3. The effect of SSSC in variation of real power transmitted through each line can be obtained by
comparing table 3 and figure5.
The SSSC is operated in real power flow mode by applying proper control signals for series controller.
Series controller injects voltage in series with the transmission line whose real power and reactive power
Figure 3: Reference Voltage Magnitudes in Each Phase
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Aswathi Krishna D. and M.R. Sindhu
Figure 4: Bus Voltages after Series Voltage Injection
has to be controlled. Equations for determining the series voltage to be injected for obtaining required P
and Q through the line are
P4 � jQ4 � (V4 �� 4 ) I *
P4 � jQ4 � (V4 �� 4 )[[(V4�� 4 ) � (V2 �� 2 )]Y ]*
'
'
*
� P4 � jQ4 �
'
'
�
� � ��(V4 �� 4 ) � (V2 �� 2 ) �� Y
� V4 �� 4 �
� 1 � P � jQ �* �
4
(V2 �� 2 ) � (V4 �� 4 ) � � � 4
� �
�� Y � V4 �� 4 � ��
'
'
(9)
6. RESULTS AND DISCUSSIONS
Static Synchronous Compensator is a FACTS device which can control the reactive and real power flow
through transmission lines. Desired amount of power flow is achieved by injecting a voltage of controlled
phase angle and magnitude in series with transmission line. The voltage injected in simulated system was
capable of increasing the real power flow through transmission line 2–4 from 0.407 p.u to the desired value
of 0.43 p.u. Power flow through each transmission line has varied accordingly so as to avoid overloading
between two neighboring buses. Power flow through the transmission lines in IEEE 5 bus system after
series voltage injection is shown in figure 13.
Application of Static Synchronous Series Compensator (SSSC) to Enhance Power Transfer...
2035
Figure 5: Power Flow through the Transmission Lines in UPFC Connected System
7.
CONCLUSION
This paper presented the performance characteristics of SSSC installed in IEEE standard 5 bus system.
Without SSSC, transmission line 2-4 shows overloading. By installing SSSC in the line, series inverter
injects real power and reactive power of 0.43 p.uand 0.14 p.u respectively. The compensation system
shows reduction in loading of the line. In both the cases, all the bus voltages are in nominal voltage limits.
Real power and reactive power losses in the system are reduced with SSSC compensation.
Acknowledgment
The authors would like to thank Amrita Vishwa Vidyapeetham and Department of science and technology
for the support for carrying out this project work.
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