 Open Access
 Total Downloads : 2150
 Authors : Ravi Kumar Hada, Sarfaraz Nawaz
 Paper ID : IJERTV1IS5054
 Volume & Issue : Volume 01, Issue 05 (July 2012)
 Published (First Online): 02082012
 ISSN (Online) : 22780181
 Publisher Name : IJERT
 License: This work is licensed under a Creative Commons Attribution 4.0 International License
Optimal location of shunt FACT devices for Power flow control in power System
Ravi Kumar Hada1, Sarfaraz Nawaz2 M.Tech. Scholar, SKIT, Jaipur, Rajasthan, India
Assistant Professor, Department of Electrical, SKIT, Jaipur, Rajasthan, India
Abstract Power flow control, in an existing long transmission line, plays a vital role in Power System area. In this the shunt connected compensation (STATCOM) based FACTS device for the control of voltage and the power flow in long distance transmission line. The proposed device is used in different locations such as sending end of the transmission line, middle and receiving end of the transmission line. The PWM control strategy is used to generate the firing pulses of the controller circuit. Simulations were carried out using MATLAB Simulink environment. The suitable location and the performance of the proposed model were examined. Based on a voltagesourced converter, the STATCOM regulates system voltage by absorbing or generating reactive power. The simulation results reveals that the reactive power generated is better at the middle of the transmission line when compared with the other ends of the transmission line and also the voltage is controlled at the middle of the line. Henceforth the location of STATCOM is optimum when connected at the middle of the line.
Keywords FACTS device, STATCOM, PWM technique, MATLAB Simulink.

INTRODUCTION
In Present scenario the applications of the power electronics devices in power systems are very much augmented. It is an urgent need to control the power flow, in a long distance transmission line. The FACTS devices are introduced in the power system transmission for the reduction of the transmission line losses, Increases Power System Stability and also to increase the transfer capability. STATCOM is VSC based controller to regulate the voltage by varying the reactive power in a long transmission line. Tan Y.L., et al[1] have demonstrated the effectiveness of SVC and STATCOM of same rating for the enhancement of power flow. Xia Jiang Xinghao Fang Chow et al [2] have focused on modelling converterbased controllers when two or more VSCs are coupled to a dc link (e.g., unified powerflow controller (UPFC), interline powerflow controller, and a generalized unified powerflow controller) and in their approach they allowed efficient implementation of various VSC operating limits, where one or more VSCs are loaded to their rated capacity. Chandrakar, V.K. et al [3] have investigated the optimal location of shunt FACTS devices in transmission line for highest possible benefit under normal condition and also they considered three different line models namely, line impedance model, reactance model and pi() model. Bebic, J.Z.[4] have presented two such topologies, the first one
consists of a shunt connected controllable source of reactive power, and two series connected voltagesourced converters – one on each side of the shunt device which is named as "hybrid power flow controllers", or HPFC. Johnson, B.K.[5] has presented an overview of how series connected and combined series/shunt connected FACTS controllers are studied in an AC system. Shankaralingappa, C.B.[6] has achieved the optimum required rating of series and shunt flexible ac transmission systems controllers for EHVAC long transmission lines by computing `optimum compensation requirement' (OCR) for different loading conditions. Shakib,
A.D. [7] has defined a sensitivity analysis, which is used to determine the area on which the FACTS device has significant influence, for the detection of sensor nodes and then only this limited area is included in the Optimal Power Flow control. Salemnia, A. et al [8] have proposed the concept of using remote signals acquired through PMU to damp SSR. K.R. Padiyar et al[9] have considered a series passive compensation and shunt active compensation provided by a static synchronous compensator (STATCOM) connected at the electrical center of the transmission line to minimize the effects of SSR. Prabhu, N. et al [10] has investigated the sub synchronous resonance (SSR) characteristics of the system and proposed a novel method for the extraction of sub synchronous component of line current using filter. Zarghami, M.et al [11] has discussed a novel approach for damping interarea oscillations in a large power network using multiple STATCOMs. Yap, E.M. et al[12] have focused on the effective utilization of a flexible alternating current transmission system (FACTS) device called unified power flow controller (UPFC) for power flow control and also demonstrated the use of the latest power system analysis toolbox (PSAT) package for network analysis of alternative means of improving existing transmission capability. Y u Liu Bhattacharya, S. et al[13] have designed a controller in which an optimal combination modulation strategy is used, which leads to some challenges in designing the controller, such as extra switching and the balancing of individual dc capacitor voltages. Larki, F. et al [14] have presented a new approach for identification of optimal locations of STATCOM and SVC and also simulated case studies conducted on Kouzestan power networks in Iran based on the proposed techniques. Albasri, F.A.et al[15] have investigated a comparative study of the performance of distance relays for transmission lines compensated by shunt connected flexible ac transmission system (FACTS) controllers.
In this paper performance strategy were conducted on STATCOM at different locations such as sending end, middle and the receiving end of the long distance transmission line. In every part of the location the power flow is tested with and without compensation strategy. In this paper also shows the effect of STATCOM on voltages of system buses and power flows in both steady state and abnormal conditions. The simulink model of the three bus system is developed and tested using MATLAB Simulink environment.

OPERATING PRINCIPLE
A STATCOM is comparable to a Synchronous Condenser (or Compensator) which can supply variable reactive power and regulate the voltage of the bus where it is connected. The equivalent circuit of a Synchronous Condenser (SC) is shown in Fig.1, which shows a variable AC voltage source (E) whose magnitude is controlled by adjusting the field current. Neglecting losses, the phase angle () difference between the generated voltage (E) and the bus voltage (V) can be assumed to be zero. By varying the magnitude of E, the reactive current supplied by SC can be varied. When E = V, the reactive current output is zero. When E > V, the SC acts as a capacitor whereas when E < V, the SC acts as an inductor. When = 0, the reactive current drawn (Ir) is given by
(1)
Fig.1 A Synchronous Condenser Fig.2 A Single Phase STATCOM
A STATCOM (previously called as static condenser (STATCON)) has a similar equivalent circuit as that of a SC. The AC voltage is directly proportional to the DC voltage (Vdc) across the capacitor (see Fig.2 which shows the circuit for a single phase STATCOM). If an energy source (a battery or a rectifier) is present on the DC side, the voltage Vdc can be held constant. The selfcommutated switchesT1 and T2 (based on say GTOs) are switched on and off once in a cycle. The conduction period of each switch is 180 and care has to be taken to see that T1 is off when T2 is on and vice versa. The diodes D1 and D2 enable the conduction of the current in the reverse direction. The charge on the capacitors ensures that the diodes are reverse biased. The voltage waveform across PN is shown in Fig.3. The voltage VPN = Vdc/2 when T1 is conducting (T is off) and VPN = Vdc/2 when T2 is conducting (and T1 is off).
Fig.3 The waveform of VPN

MODELING OF STATCOM
Based on the operating principle of the STATCOM, the equivalent circuit can be derived, which is given in Fig.4. In the derivation, it is assumed that (a) harmonics generated by the STATCOM are neglected; (b) the system as well as the STATCOM are three phase balanced.
Then the STATCOM can be equivalently represented by a controllable fundamental frequency positive sequence voltage source Vsh. In principle, the STATCOM output voltage can be regulated such that the reactive power of the STATCOM can be changed.
Fig.4 STATCOM Equivalent Circuit
According to the equivalent circuit of the STATCOM shown in Fig.4, suppose Vsh = Vshsh , Vi = Vi i , then the power flow constraint of the STATCOM are:
(2)
(3)
Where
.
The operating constraint of the STATCOM is the active power exchange via the DC link as described by:
(4)
Where

SIMULATION MODEL
(5)
the "natural" power flow on the transmission line is 951.4 MW from bus B1 to B3. STATCOM has a rating of +/ 100MVA. This STATCOM is a phasor model of a typical threelevel PWM STATCOM.
Fig.5 explains about the circuit diagram without compensation. In this circuit the power is directly measured in the 600km long transmission line at the three stages like B1,
Here we considered a three bus Power system which consists of two 500KV equivalents generators, respectively 3000 MVA and 2500 MVA, connected by a 600km long transmission line. When the STATCOM is not in operation,
B2 and B3 and also tabulated the result in table1. Fig.6 explains about the circuit diagram when STATCOM is connected at the Middle of the long transmission line. Similarly the connections are made when the STATCOM is connected at the sending end and receiving end of the long transmission line.
Fig.5 Simulink Model of Power System without compensation
Fig.6 Simulink Model of Power System with STATCOM at Middle

SIMULATION RESULTS
To understand the Effect of presence of STATCOM in system, on system parameters, typical cases we have carried out by simulation analysis of the system. The results are generated by MATLAB outputs shown on respective cases. The results of cases are tabulated, analyzed and compared which clearly shows the Effect of the STATCOM under various conditions. The cases are as under.

Effect on Power flows at B1, B2 and B3 in Steady State
980
960
940
920
Real Power in MW
900
880
860
840
820
800
780
Plot of Real Power/Time
B1 B2 B3
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8
Time in sec
Fig.9 Real Power at B1, B2 & B3 when STATCOM is at Sending End
Operation (Case1)

Effect on Power flows at B1, B2 and B3 in HV and LV Condition (Case2)

Effect on Power flows at B1, B2 and B3 in Increasing Load Condition (Case3)

Effect on Voltages of System buses at B1, B2 and B3 for steady state, HV, LV and increasing load condition (Case4)

Effect on Power flows due to Optimal Location of STATCOM (Case5)
100
50
Reactive Power in MVAr
0
50
100
Plot of Reactive Power/Time
B1 B2
B3

Case1
150
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8
Time in sec
Fig.7 and Fig.8 highlights the real and reactive power control at the three stages when the STATCOM is not connected i.e. without compensation.
Fig.10 Reactive Power at B1, B2 & B3 when STATCOM is at Sending End

Case2
Fig.11 and Fig.12 highlights the real and reactive power
960
940
920
900
Plot of Real Power/Time
control at the three stages when the STATCOM is not connected i.e. without compensation in HV Condition. Fig.13
B1 B2
B3
and Fig.14 highlights the real and reactive power control at the three stages when the STATCOM is not connected i.e. without compensation in LV Condition.
Real Power in MW
880
B1
B2
B3
1060
Plot of Real Power/Time
860
840
820
800
0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.1
Time in sec
Fig.7 Real Power at B1, B2 & B3 without compensation
Plot of Reactive Power/Time
B1
B2
B3
80
60
1040
1020
1000
Real Power in MW
980
960
940
920
900
880
40
0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.1
Time in sec
Fig.11 Real Power at B1, B2 & B3 without compensation for High voltage
Reactive Power in MVAr
20 condition
B1
B2
B3
0 100
Plot of Reactive Power/Time
20
40
60
80
100
0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.1
Time in sec
Fig.8 Reactive Power at B1, B2 & B3 without compensation
80
60
40
Reactive Power in MVAr
20
0
20
40
60
80
Fig.9 and Fig.10 highlights the real and reactive power control at the three stages when the STATCOM is connected at
100
120
0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.1
Time in sec
Sending End i.e. with compensation.
Fig.12 Reactive Power at B1, B2 & B3 without compensation for High
voltage condition
880
860
840
Real Power in MW
820
800
780
760
740
Plot of Real Power/Time
900
880
860
840
Real Power in MW
820
800
780
760
740
B1
B2 B3
Plot of Real Power/Time
B1
B2 B3
720
0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.1
Time in sec
720
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8
Time in sec
Fig.13 Real Power at B1, B2 & B3 without compensation for Low voltage condition
Plot of Reactive Power/Time
B1
B2 B3
80
60
40
Reactive Power in MVAr
20
0
20
40
60
80
Fig.17 Real Power at B1, B2 & B3 when STATCOM is at Sending End for low voltage Condition
Plot of Reactive Power/Time
100
B1 B2
80 B3
60
40
Reactive Power in MVAr
20
0
20
40
60
80
100
0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.1
Time in sec
100
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8
Time in sec
Fig.14 Reactive Power at B1, B2 & B3 without compensation for Low voltage condition
Fig.15 and Fig.16 highlights the real and reactive power control at the three stages when the STATCOM is connected at Sending End i.e. with compensation in HV Condition. Fig.17 and Fig.18 highlights the real and reactive power control at the three stages when the STATCOM is connected at Sending End i.e. with compensation in LV Condition.
Fig.18 Reactive Power at B1, B2 & B3 when STATCOM is at Sending End for Low voltage Condition

Case3
Fig.19 and Fig.20 highlights the real and reactive power control at the three stages when the STATCOM is not connected i.e. without compensation in Increasing Load Condition.
Plot of Real Power/Time
B1
B2 B3
1000
1060
1040
1020
1000
Real Power in MW
980
960
940
920
900
Plot of Real Power/Time
B1 B2
B3 950
Real Power in MW
900
850
800
750
880
860
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8
Time in sec
0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.1
Time in sec
Fig.19 Real Power at B1, B2 & B3 without compensation for Increasing Load
Plot of Reactive Power/Time
B1
B2 B3
60
Fig.15 Real Power at B1, B2 & B3 when STATCOM is at Sending End for high voltage Condition
Plot of Reactive Power/Time
80
60
40
20
Reactive Power in MVAr
0
20
40
60
40
20
Reactive Power in MVAr
0
20
40
60
80
100
120
0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.1
Time in sec
80
100
120
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8
Time in sec
Fig.16 Reactive Power at B1, B2 & B3 when STATCOM is at Sending End for high voltage Condition
Fig.20 Reactive Power at B1, B2 & B3 without compensation for Increasing Load
Fig.21 and Fig.22 highlights the real and reactive power control at the three stages when the STATCOM is connected
at Sending End i.e. with compensation in Increasing Load Condition.
B2
B1
B3
0.975
Plot of Voltage/Time
1050
1000
950
Real Power in MW
900
850
800
750
Plot of Real Power/Time
0.97
0.965
Voltages in pu
0.96
0.955
0.95
0.945
0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.1
Time in sec
700
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8
Time in sec
Fig.25 Voltages of system bus B1, B2 and B3 without compensation for Low Voltage Condition
Fig.21 Real Power at B1, B2 & B3 when STATCOM is at sending end for
B2
B3
B1
Increasing Load Condition 1
Plot of Reactive Power/Time
Plot of Voltage/Time
80
60
40
20
Reactive Power in MVAr
0
20
40
60
80
100
0.995
Voltages in pu
0.99
0.985
0.98
0.975
0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.1
Time in sec
120
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8
Time in sec
Fig.22 Reactive Power at B1, B2 & B3 when STATCOM is at sending end for Increasing Load Condition

Case4
Fig.23 to Fig.26 highlights the Voltages at the three stages when the STATCOM is not connected i.e. without
Fig.26 Voltages of system bus B1, B2 and B3 without compensation for Increasing Load Condition
Fig.27 to Fig.30 highlights the voltages at the three stages when the STATCOM is connected at Sending End i.e. with compensation in Steady State, HV, LV and Increasing Load Condition respectively.
compensation in Steady State, HV, LV and Increasing Load Condition respectively.
Plot of Voltage/Time
B2
B1
1.025
1.02
1.015
Voltages in pu
1.01
1.005
1.035
1.03
1.025
1.02
Voltages in pu
1.015
1.01
1.005
1
0.995
0.99
Plot of Voltage/Time
1 B3
0.985
B2
B1
B3
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8
Time in sec
0.995
0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.1
Time in sec
Fig.27 Voltages of system bus B1, B2 and B3 with compensation for Steady state Condition
Fig.23 Voltages of system bus B1, B2 and B3 without compensation for
Steady state Condition
Plot of Voltage/Time
1.07
Plot of Voltage/Time
B2
B1
B3
1.08
1.075
1.07
Voltages in pu
1.065
1.06
1.055
1.05
1.045
0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.1
Time in sec
Fig.24 Voltages of system bus B1, B2 and B3 without compensation for High Voltage Condition
1.065
B2
B1
B3
1.06
1.055
Voltages in pu
1.05
1.045
1.04
1.035
1.03
1.025
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8
Time in sec
Fig.28 Voltages of system bus B1, B2 and B3 with compensation for High voltage Condition
Plot of Voltage/Time
B2
B1
B3
1
960
Plot of Real Power/Time
0.99
0.98
Voltages in pu
0.97
0.96
0.95
0.94
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8
Time in sec
Fig.29 Voltages of system bus B1, B2 and B3 with compensation for Low voltage Condition
940
920
900
Real Power in MW
880
860
840
820
800
780
B1 B2 B3
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8
Time in sec
Fig.33 Real Power at B1, B2 & B3 when STATCOM is at Middle
Plot of Reactive Power/Time
1.03
1.02
1.01
Voltages in pu
1
0.99
Plot of Voltage/Time
100
B1 B2 B3
50
Reactive Power in MVAr
0
50
100
B2
B3
B1
0.98
0.97
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8
Time in sec
150
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8
Time in sec
Fig.34 Reactive Power at B1, B2 & B3 when STATCOM is at Middle
Fig.30 Voltages of system bus B1, B2 and B3 with compensation for Increasing Load Condition

Case5
Fig.35 and Fig.36 highlights the real and reactive power control at the three stages when the STATCOM is connected at Receiving End.
Fig.31 and Fig.32 highlights the real and reactive power control at the three stages when the STATCOM is connected at Sending End.
980
960
940
920
Plot of Real Power/Time
B1 B2 B3
980
960
940
920
Real Power in MW
900
880
860
840
B1 B2 B3
Plot of Real Power/Time
Real Power in MW
900
880
860
840
820
800
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8
Time in sec
Fig.35 Real Power at B1, B2 & B3 when STATCOM is at Receiving End
Plot of Reactive Power/Time
820
800
780
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8
Time in sec
Fig.31 Real Power at B1, B2 & B3 when STATCOM is at Sending End
Plot of Reactive Power/Time
150
B1 B2 B3
100
50
B1 B2 B3
100
50
Reactive Power in MVAr
0
50
0
Reactive Power in MVAr
50
100
150
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8
Time in sec
100
150
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8
Time in sec
Fig.32 Reactive Power at B1, B2 & B3 when STATCOM is at Sending End
Fig.33 and Fig.34 highlights the real and reactive power control at the three stages when the STATCOM is connected at Middle.
Fig.36 Reactive Power at B1, B2 & B3 when STATCOM is at Receiving End


CONCLUSION
The vital role of shunt FACTS devices, which are connected in long distance transmission lines, are to improve the power transfer capability and also to control the power flow in the power system network. In this proposed work STATCOM is
employed as a shunt FACTS device. STATCOM is connected at the various locations such as sending end, middle and receiving end of the transmission line. The results were obtained with and without compensation. The simulation results reveals that the reactive power generated is better at the middle of the transmission line when compared with the other ends of the transmission line and also the voltage is controlled at the middle of the line. So, the location of STATCOM is optimum when connected at the middle of the line.
IEEE Conference on TENCON 2009, pp 16, Jan.2009.

Zarghami, M. Crow, M.L. Damping interarea oscillations in power systems by STATCOMs, 40th North American Symposium 2008, pp 16, 9781 424442836, Sept 2008.
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TABLE I

Yap, E.M. AlDabbagh, M. Thum, P.C. Applications of FACTS Controller for Improving Power Transmission Capabiity, IEEE Conference on TENCON 2005, pp 16, Nov 2005.
Bus Number 
STATCOM at Sending End 
STATCOM at Middle 
STATCOM at Receiving End 

P in MW 
Q in MVAr 
P in MW 
Q in MVAr 
P in MW 
Q in MVAr 

B1 
947.5 
99.1 
940.1 
79.97 
952.5 
99.61 
B2 
826 
56.34 
820.5 
37.43 
830.2 
54.79 
B3 
812.1 
67.95 
806.5 
56.36 
816.2 
74.8 
General Meeting, DOI10.1109/PES.2006.1708944, Oct 2006.

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COMPARISON OF P & Q