Al-Qadisiya Journal For Engineering Sciences, Vol. 7……No. 3 ….2014 092 STATCOM Application in 400kv Iraqi Super Grid for Voltage Magnitude Improvement Shatha S. Abdulla Al-Kubragyi University of Technology Electrical Department Shatha_suhbet@yahoo.com Received 20 Feb 2014 Accepted 16 July 2014 ABSTRACT This paper presents a study of static synchronous compensator (STATCOM). One of the Flexible AC Transmission System (FACTS) devices, it can significantly improve power systems stability. Consisting of voltage sourced converters connected to an energy storage device on one side and to the power system on the other, it specifically can provide reactive support to buses. This work presents a simple algorithm for identifying weak buses to determine the best location for STATCOM. Singularity of the power flow Jacobian matrix as an indicator of steady-state stability has used, the sign of the determinant of the load flow Jacobian was used to determine the system stability, by computing eigenvalues, eigenvectors , minimum singular value of load- flow Jacobian Matrix and sensitivity analysis between power flow and bus voltage changes. Load flow analysis of the Iraqi grid 400 KV network has been carried out using Newton- Rephson Method with and without STATCOM. The result of Load flow analysis show improvement in bus voltage with the use of STATCOM in the system. Keywords: Fact, Statcom, Load flow, Voltage Stability. الفولتية قيمة( لتحسين 044)Kv عراقية ال الفائق في شبكةالضغط STATCOMتطبيق شذى صحبت عبدهللا الكبراغي الجامعة التكنولوجية قسم الهندسة الكهربائية الخالصة: يث،ح المرنة المتردد التيار نقل نظام أجهزة من واحد .(STATCOM) المتزامن المعوض ثابت دراسة تم البحث هذا في على الطاقة تخزين جهاز إلى متصلة الجهد مصادر محوالت من يتكون. الطاقة أنظمة استقرار كبير حد إلى يحسن أن يمكن .التفاعلية بالقدرة bus لل دعم توفر أن يمكن التحديد وجه على فإنه أخرى، جهة من الطاقة ونظام واحد جانب استخدمت ،STATCOMل موقع أفضل لتحديد الضعيفة buses لتحديد يطةبس خوارزمية على االعتماد تم العمل هذا في singularity لمصفوفة المحدد أشارة اعتماد تم ،حيث النظام استقرارية على كمؤشر الطاقة لتدفق جاكوبين لمصفوفة الذاتية هاتالمتج ،(eigenvalue) الذاتية القيم حساب خالل من النظام، استقرار لتحديد الحمل لتدفق جاكوبين (eigenvectors) ، وminimum singular value تدفق بين االستجابة وتحليل لسريان الحمل جاكوبين لمصفوفة .الجهد مجمع وتغيرات الطاقة mailto:Shatha_suhbet@yahoo.com Al-Qadisiya Journal For Engineering Sciences, Vol. 7……No. 3 ….2014 092 التحليل ونتائج .STATCOM وبدون مع رافسن نيوتن طريقة باستخدام كف ٠٤٤ العراقية للشبكة الحمل سريان تحليل تم .النظام في STATCOM بأستخدام bus voltage)) الجهد مجمع في تحسنا تأظهر ., سريان الحمل , استقرارية الفولتية ,Fact , Statcomالكلمات الرئيسة : List of symbols: FACTS: Flexible Ac Transmissions System. ISG: Iraqi Super Grid. STATCOM: Static Synchronous Compensator. , active and reactive power mismatch , voltage magnitude and voltage angle mismatch 𝜕 𝜕 : Partial derivatives of the real and reactive power. 𝜕 𝜕 : Partial derivatives of the voltage magnitude and voltage angle . Y admittance :mismatch active power at kih bus in i iteration  k i Q : mismatch reactive power at kih bus in i iteration specified accuracy for active and reactive power mismatch J Jacobin matrix JR reduced Jacobin matrix right and left eigenvector of matrix JR diagonal eigenvalue of matrix JR the ith eigenvalue. the ith of column right eigenvector. the ith of row left eigenvector ith modal reactive power variation Ki Normalization factor. Pki Participation factor of the kth bus in ith mode . Pk ,Qk active and reactive power injection at bus k. Vk voltage at bus k Vj voltage at bus j. Ykj admittance between bus k and bus j.  k i P Al-Qadisiya Journal For Engineering Sciences, Vol. 7……No. 3 ….2014 090 PSTAT STATCOM active power. QSTAT STATCOM reactive power. STATCOM voltage. STATCOM admittance. GSTAT , BSTAT conductance and suspectance of STATCOM. 1. INTRODUCTION Voltage control and stability problems are not new in the electric power system industry but are now receiving special attentions. Voltage stability is the ability of a power system to maintain voltage irrespective of the increase in load admittance and load power resulting in control of power and voltage [1]. A system is said to enter a state of voltage instability when a disturbance causes a progressive and uncontrollable decline in voltage, which can occur because of the inability of the network to meet the increased demand for reactive power [2], which lead in the worst case, in the collapse of the power system. Appropriate voltage and reactive power control are one of the most important factors for stable power system. Where, the distribution system losses and various power quality problems are increasing due to reactive power [3]. There are several studies [2, 4, 5] focused on measures to predict system conditions with respect to voltage stability and optimal control actions to avoid collapse in the online paradigm. As most of these problems are highly nonlinear and computationally intensive, there is a need of research to help in reducing computation and using direct measurements for estimation of stability margin. Many analysis methods [6, 7] of voltage stability determination have been developed based on the load flow solution, optimal power flow, bifurcation technique, singularity of Jacobin etc. Different voltage stability indicators have also been established covering both static and dynamic aspects of the problem. Efforts also have been made to assess the voltage stability of large power systems in terms of network equivalents to obtain the global picture of voltage stability [2]. Now, more than ever, advanced technologies are paramount for the reliable and secure operation of power systems. Power electronic based equipment, such as FACTS controllers, are the most effective way for utilities to improve voltage stability of the system with their capability to respond rapidly the system events, increase power transfer limits, and improve the quality of power delivered, constitute one of the most-promising technical advancements to address the new operating challenges being presented today [8].The Static synchronous Compensator (STATCOM) is one of the most important FACTS devices, a regulating device used on alternating current electricity transmission networks and it is based on the principle that a voltage-source inverter generates a controllable AC voltage source behind a transformer leakage reactance so that the voltage difference across the reactance produces active and reactive power exchange between the STATCOM and the transmission network [9, 10]. This paper focuses on one such FACTS controller for voltage support as a reactive power (VAR) source, namely the static compensator (STATCOM). A systematic analytical methodology based on modal analysis of the modified load flow Jacobian matrix has been used as a static voltage stability index to determine the best location for STATCOM. Al-Qadisiya Journal For Engineering Sciences, Vol. 7……No. 3 ….2014 092 2. POWER FLOW SOLUTION A power flow or load flow program computes the voltage magnitude and angle at each bus in a power system. Once they are calculated, real and reactive power flows for all equipment interconnecting the buses, as well as losses are also computed. There are two ways to represent the bus voltage equations to solve the load flow problem, the rectangular and polar coordinates of bus voltages. It is prefer to use polar coordinates to formulate the power flow equation. As the power flow method is implemented for voltage stability analysis, the Jacobian matrix of solved load flow equations, by Newton-Raphson method, can be used. The linearized steady-state system power voltage equation is expressed as [11]: [ ] [ | | | | ] [ | | ] (1) The Jacobin matrix can be written as: [ ] [ ] [ | | ] (2) The Jacobian matrix gives the linearized relationship between small changes in voltage angle and the voltage magnitude with the small changes in real and reactive power mismatch and . Elements of the Jacobian matrix are partial derivatives of the real and reactive power, evaluated at and .and for more details in [9, 11]. The procedure for power flow solution by the Newton-Raphson method is as follows: 1. Read system and load data (including identified the slack bus, generator bus (PV) bus, and load bus PQ ). 2. Form the nodal admittance matrix [Y]. 3. Initialize δ, V 4. Calculate P and Q. 5. Calculate Jacobian matrix (2. through 1). 6. Solve for the voltage angle and magnitude. 7. Update the voltage magnitude and angles. Al-Qadisiya Journal For Engineering Sciences, Vol. 7……No. 3 ….2014 092 8. Check the stopping conditions. If met then terminate, else go to step 3.         k i k i Q P To express the relation between Q and V For small change in real power P=0 is assumed So that equation (2) leads to be: VJJP  12110  VJJ   12 1 11 (3) And VJJQ  2221  (4) Substituting Equation (3) in Equation (4): VJJJ J Q   ) 22 ( 12 1 1121 (5) The expression in the brackets in (5) represents the reduced Jacobian matrix RJ of the system. It relates the bus voltage magnitude and reactive power injection. The eigenvalues and eigenvectors of the reduced order Jacobin matrix RJ are used for the voltage stability characteristics analysis. Voltage instability can be detected by identifying modes of the eigenvalues matrix RJ . The magnitude of the eigenvalues provides a relative measure of proximity to instability. The eigenvectors on the other hand present information related to the mechanism of loss of voltage stability. Let assume  .. 12 1 1121 22    JJJ JR J (6) Al-Qadisiya Journal For Engineering Sciences, Vol. 7……No. 3 ….2014 092 Where: ξ= right eigenvector matrix of RJ  = left eigenvector matrix of RJ  = diagonal eigenvalue matrix of RJ . Equation (6) can be written as:  11   R J (7) Using equation (1) and (2) the incremental changes in reactive power and voltage are related by: (8) Or QV i i     (9) Where i is the th i eigenvalue, is the th i of column right eigenvector and is the th i of row left eigenvector of matrix RJ . i ,ξi, and I define the i th mode of the system. The th i modal reactive power variation is: imi KQ  ξ i (10) Where iK is a normalization factor The appropriate definition and determination as to which node or load bus participates in the selected modes become very important. This necessitates a tool, called the participation factor, for identifying the weakest nodes or load buses that are Al-Qadisiya Journal For Engineering Sciences, Vol. 7……No. 3 ….2014 092 making significant contribution to the selected mode and is suitable for STATCOM placement. If ξ and represent the right and left hand eigenvectors, respectively, for the eigenvalue λi of the matrix JR, then the participation factor measuring the participation of the kth bus in ith mode is defined as [11,12 ]: such that ∑ (11) With ξji the th J element of ξ i The corresponding th i modal voltage variation can therefore be written as: mi i mi QV   1 (12) Pki = (13) 3. STATCOM – STATIC SYNCHRONOUS COMPENSATOR The STASTCOM is one of the important shunt connected ‘Flexible AC Transmission system’ consisting of a power electronics device connected with a capacitor or reactance. A step down transformer, called coupling transformer, is needed to reduce the voltage level of the bus where the STATCOM is installed as shown in the Figure (1) [13]. It regulates the voltage at its terminals in power system, having as an ultimate goal the increase in transmittable power, and improvements of steady state transmission characteristics and of the overall stability of the system. Under light load conditions, the controller is used to minimize or completely diminish line over voltage; on the other hand, it can be also used to maintain certain voltage levels under heavy loading conditions [14]. Some papers discuss how to model STATCOM for load flow calculation. So, The bus at which the STATCOM is connected is represented as a PV bus , which may change to a PQ bus in the events of limits being violated depending on its primary application.. In such a case, the generated or absorbed reactive power would correspond to the violated limit, the STATCOM is represented as a voltage source for the full range of operation, enabling a more robust voltage support mechanism. In a load flow calculation, a STATCOM is typically treated as a shunt reactive power controller assuming that it can adjust its injected reactive power to control the voltage at the STATCOM terminal bus [11, 15]. This means that the STATCOM absorbs proper amount of reactive power . The power system to keep Vk constant for all power system loading within reasonable range, the ohmic loss of the STATCOM is accounted by considering the real part of Ystatin power flow calculations. The net active/reactive power injection at bus k including the local load, before addition of the STATCOM, is known by Pk+jQk. The power flow equations of the system with STATCOM connected to Bus k, can written as [16]: Al-Qadisiya Journal For Engineering Sciences, Vol. 7……No. 3 ….2014 092 ∑ | | | || | (14) ∑ | | | || | (15) | | | || || | (16) | | | || || | (17) For more detail in [16].Figure (2) depicts a STATCOM and the traditional simple model used in this paper for load flow calculation. In this model reactive power load at bus i, jQi, is combined with STATCOM reactive power output[11, 15], and Figure (3) show the flow chart for Power Flow Solution by Newton-Raphson with STATCOM. 4. CASE STUDY The Iraq super grid transmission line is large system having two voltage levels 400Kv and 132Kv; the network under consideration in this work is the 400Kv super grid (ISG). This network contains twenty four bus bar connecting with fourteen transmission line. The generation unit in the system are distributed at the twelve buses for the grid. The single line diagram ISG for is shown in the Figure (4). The bus data with power demand, generation are given in the data information illustrated in table (1). Table (2) presents the load flow output results by using Newton-Raphson method. The system has one swing bus and eleven P-V bus so the total number eigenvalue of the reduced Jacobin matrix  RJ is expected to be (12), After employing eigenvalues at each load level, the buses are ranked in the order of the value of participation factor for these buses: the top ranked bus in the priority list has the greatest participation factor and refers as the weakest from others. The results of the eigenvalues and the participation factor are tabulated in the tables (3). Note from the table all the Eigenvalues are positive which means that the system voltage is stable. Figure (5) shows the participating factor for the minimum Eigenvalues of the system. It can be seen that the bus (19), (18) and (15) bus have the highest participation factor value to the critical mode. So, the most optimal bus to install STATCOM are buses 19, 18 and 15 respectively, 24-bus test system is used to assess the effectiveness of STATCOM model developed in this paper. The voltage profile of all buses without STATCOM is described in Figure (6). It can be seen that all the bus voltage are within the acceptable level (±5%), the lowest voltage compared to the other buses can be noticed in bus number 24. The voltage profile of all buses with statcom installation at bus 19 and 15 also shown in Figure (6). 5. CONCLUSION STATCOM devices present an effective device in employing for voltage stability enhancement. The load flow studies are carried out with and without STATCOM and Newton-Raphson method is used in Load flow. Due to the high cost of FACTS controllers which improves voltage stability, FACTS Devices installed localization studies is important to prevent additional costs. In this paper modal analysis algorithm for optimal location of STATCOM was used. The modal analysis provided important information about the proximity of the system to voltage instability. The results showed that the STATCOM can be used to improve an overall network voltage profile in practical power systems. Additionally, in general more reactive power was available in Al-Qadisiya Journal For Engineering Sciences, Vol. 7……No. 3 ….2014 092 the network with STATCOM installed than without. The STATCOM and the detailed simulation are performed using Matlab program. REFERENCES [1]. D. Bică, “Static Voltage Stability Analysis By Participation Factors Computing, Scientific Bulletin of the PetruMaior”, University of Targu Mures Vol. 2 , 2006. [2]. S. H. Palukuru and S. Paul, “Global Voltage Stability Analysis of a Power System Using Network Equivalence Technique in the Presence of TCSC”, Leonardo Electronic Journal of Practices and Technologies, Issue 16, January-June 2010. [3] . S. Sundarsingh, Dr. R. Raja Prabu , “Performance of Thirty Bus System with and without STATCOM” ,International Conference on Trends in Electrical, Electronics and Power Engineering July 15-16, 2012. [4]. C. K. Babulal, P. S. Kannan and J. Maryanita, “A Novel Approach to Determine Static Voltage Stability Limit and Its Improvement Using TCSC and SVC”, Journal of Energy & Environment, Vol. 5, May 2006. [5]. W. Zhang, F. Li, and L. M. Tolbert , “Optimal Allocation of Shunt Dynamic VarSource SVC and STATCOM” A SurveyElectrical and Computer Engineering, The University of Tennessee. [6]. M. S. Saad, and A. Edris , “Delaying Instability and Voltage Collapse in Power Systems using SVCs with Washout Filter-Aided Feedback”, American Control Conference, June 8-10, 2005. [7]. R.Alammari, “The Voltage Collapse Problem Based on The Power System Loadability”, Engineering Journal of University of Qatar, Vol. 10, 1997. [8] .H. Yonezawa , M. Tsukada and J. “Paserba,Study of a STATCOM Application for Voltage StabilityEvaluated by Dynamic PV Curves and Time Simulations” ,Power Engineering Society Winter Meeting, conference , Vol. 2, 23 -27 Jan 2000. [9]. H. Boroujeni, M.Amani and M.Abdollahi, “Dynamic Stability Improvement by Using STATCOM in a Multi Machine Environment”, Research Journal of Applied Sciences, Engineering and Technology 4(18): 3505-3509, 2012. [10] . M .Kamarposhti “ Evaluation of Static Synchronous Compensator In Order to Loading Margin Study In Power System ” Indian Journal of Science and Technology Vol. 3 No. 5 , ISSN: PP 0974- 6846. (May 2010) . [11]. A. Kazemi H.A. ShayanfarM.andA. Rafiee, “Impact of STATCOM and OPF on Power System Voltage StabilityUsing Modal Analysis and Quadratic Programming” ,Proceedings of The 12 th Iranian Electrical Engineering Conference , Vol. 1, PP. 25-29, Mashhad , May 11-13 , 2004 IRAN. [12] .C. R. “Hemavathi,PredicationOf Voltage Stability by Using Modal Analysis”, National Conference On Electrical Sciences -2012 (NCES-12). http://ieeexplore.ieee.org/xpl/mostRecentIssue.jsp?punumber=6841 http://ieeexplore.ieee.org/xpl/mostRecentIssue.jsp?punumber=6841 Al-Qadisiya Journal For Engineering Sciences, Vol. 7……No. 3 ….2014 099 [13]. E. Tobaji1, M. Khaldi2 and D. Fadel3 , “STATCOM Control of Ill-Conditioned Power Systems Using”, Advance in Electronic and Electric Engineering,, Volume 3, Number 3 ,PP . 311-320, India. 2013. [14]. P. Bisen and A. Shrivastava, “Voltage Level Improvement of Power System by the Use of STATCOM & UPFC with PSS Controller” ,International Journal of Electrical, Electronics and Computer Engineering Val 2(2): PP 117-126 (2013). [15] .H. Marefatjou1, I. Soltani2, “Optimal Placement of STATCOM to Voltage Stability Improvement and Reduce Power Losses by Using QPSO Algorithm”, Journal of Science and Engineering Vol. 2 (2), PP 105-119,Iran 2013. [16]. G. A. Adepoju, , O.A. Komolafe, “Analysis and Modelling of Static Synchronous Compensator (STATCOM): A comparison of Power Injection and Current Injection Models in Power Flow Study”, International Journal of Advanced Science and Technology Vol. 36, November, 2011. Table (1): bus data information for ISG Bus No. Bus Name Voltage (P.U.) Angle (degree) Generation Load MW MVAR MW MVAR 1. MUSP 1.04 0.0 - - 1.997795 1.166333 2. MMDH 1.015 0.0 690.1 0 000 0 3. BAJP 1.02 0.0 406.0 0 124.8622 92.2467 4. BAJG 1.02 0.0 590.458 0 0 0 5. KRK4 1.017 0.0 239.87 0 129.8567 10.4896 6. MUSG 1.02 0.0 369.04 0 0 0 7. HDTH 1.02 0.0 202.97 0 200.0540 50.612 8. QDSG 1.01 0.0 735.305 0 0 0 9. KAZG 1.0096 0.0 207.583 0 200.0419 100.6579 10. HRTP 1.01 0.0 332.133 0 154.8291 72.1171 Al-Qadisiya Journal For Engineering Sciences, Vol. 7……No. 3 ….2014 222 Table (2): bus solution for ISG Bus No. Voltage (P.U.) Angle (degree) Generation Load MW MVAR MW MVAR 1. 1.04 0 679.69 2422.66 1.997795 1.166333 2. 1.015 8.4837 690.1 58.06 000 0 3. 1.02 5.7762 406.0 -35.98 124.8622 92.2467 4. 1.02 5.8258 590.458 -65.46 0 0 11. NSRP 1.02 0.0 775.0 0 422.8665 100.3219 12. DYL4 1.00 0.0 0 0 83.2415 21.1712 13. BGW4 1.00 0.0 0 0 576.031 302.4481 14. BGN4 1.00 0.0 0 0 412.8776 139.1261 15. BGE4 1.00 0.0 0 0 849.0627 294.6579 16. QIM4 1.00 0.0 0 0 109.8787 39.3182 17. BGC4 1.00 0.0 0 0 49.9449 181.4688 18. BGS4 1.00 0.0 0 0 0 0 19. AMN4 1.015 0.0 184.518 0 126.5640 56.0014 20. MSL4 1.00 0.0 0 0 649.2833 302.4481 21. BAB4 1.00 0.0 0 0 307.9934 184.6695 22. KDS4 1.00 0.0 0 0 213.0981 151.4458 23. KUT4 1.00 0.0 0 0 259.7134 108.1756 24. AMR4 1.00 0.0 0 0 311.0221 160.3709 Al-Qadisiya Journal For Engineering Sciences, Vol. 7……No. 3 ….2014 222 5. 1.017 4.5233 239.87 -76.88 129.8567 10.4896 6. 1.02 0.2260 369.04 -2016.6 0 0 7. 1.02 1.9 202.97 -40.51 200.0540 50.612 8. 1.01 -0.8491 735.305 136.84 0 0 9. 1.0096 -3.4122 207.583 -4.77 200.0419 100.6579 10. 1.01 -4.0027 332.133 87.22 154.8291 72.1171 11. 1.02 -1.480 775.0 -48.14 422.8665 100.3219 12. 1.015 -1.3931 184.518 207.65 126.5640 56.0014 13. 1.0038 -0.8865 0 0 83.2415 21.1712 14. 1.0085 -1.1285 0 0 576.031 302.4481 15. 1.0086 -1.6927 0 0 412.8776 139.1261 16. 1.0163 0.4494 0 0 849.0627 294.6579 17. 1.0045 -0.8865 0 0 109.8787 39.3182 18. 1.0202 -0.8152 0 0 49.9449 181.4688 19. 1.0118 -0.9587 0 0 0 0 20. 1.0053 6.2414 0 0 649.2833 302.4481 21. 1.0334 -0.8086 0 0 307.9934 184.6695 22. 1.0274 -1.6149 0 0 213.0981 151.4458 23. 1.0018 -7.107 0 0 259.7134 108.1756 24. 0.9899 -8.048 0 0 311.0221 160.3709 Al-Qadisiya Journal For Engineering Sciences, Vol. 7……No. 3 ….2014 220 Table (3): eigenvalue and participation factor magnitude for ISG Bus number Eigen value Participation factor 13 2109.374 1.583*10 -12 14 906.961 1.146*10 -9 15 684.1398 1.050*10 -8 16 473.233 8.6997*10 -9 17 449.863 8.687*10 -21 18 119.394 1.168*10 -6 19 134.423 3.523*10 -6 20 130.824 1.379*10 -20 21 77.0474 3.334*10 -10 22 30.662 1.971*10 -10 23 224.595 7.685*10 -20 24 41.712 2.552*10 -19 Figure. (1). STATCOM Configuration AC System Bus Coupling Transformer Leakage Reactance Vdc cdc VSC Al-Qadisiya Journal For Engineering Sciences, Vol. 7……No. 3 ….2014 222 Figure (2): Model of STATCOM in load flow calculation Figure (3): Power Flow Solution by Newton-Raphson with STATCOM Pi +jQ-j Qc STATCOM Bus i jQc Pi+jQi Bus i start Input system data Form system admittance matrix Form conventional Jacobin Matrix Modify Jacobin Matrix and Mismatch Power Equation Update system Bus bars Voltages Is the convergence Output Load flow Results End Yes No Al-Qadisiya Journal For Engineering Sciences, Vol. 7……No. 3 ….2014 222 . Figure (4): Configuration of the ISG Al-Qadisiya Journal For Engineering Sciences, Vol. 7……No. 3 ….2014 222 Figure (5): the participating factor profile for the minimum Eigenvalues of the ISG Figure (6): voltage of all buses with and without STATCOM. 0.96 0.97 0.98 0.99 1 1.01 1.02 1.03 1.04 1.05 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 V o lt a g e s M a g n it u d e i n P .U Bus Number. without STATCOM with STATCOM