Optimal Location of TCSC to Improve Voltage Stability and Voltage Profile

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1 Optimal Location of TCSC to Improve Voltage Stability and Voltage Profile Nikunj B. Marviya Member IEEE Abstract With the inter connection of the power system, the complexity increases day by day. The increasing of the load also favours to the complexity of power system. The complexity of the power system can easily handled by analyzing the performance of the transmission system by using load flows. The real and reactive power losses are largely effected at the transmission level. With the advancement in power electronics, the advanced compensation devices are improved which are called FACTS. Flexible Alternating Current Transmission Systems (FACTS) devices have been proposed as an effective solution for controlling power flow and regulating bus voltage in electrical power systems, resulting in an increased transfer capability, low system losses, and improve stability. However to what extent the performance of FACTS devices can be brought out highly depends upon the location and the parameters of these devices. In this paper, we propose three Evolutionary Optimization Techniques, namely Genetic Algorithm (GA), Particle Swarm Optimization (PSO) and Dragonfly Algorithm (DA) to select the optimal location and the optimal parameter setting of TCSC,, firing angle of TCSC and size of the TCSC which minimize the active power losses and improves the voltage profiles in the power network, and compare their performances. To show the validity of the proposed techniques and for comparison purposes, simulations are carried out on IEEE-57 bus power system. Index Terms Power system, Transmission system, FACTS, TCSC, Firing Angle, Heuristic algorithms (GA,PSO & DA). I. INTRODUCTION With ever-increasing demand for electricity, the power transfer grows, consequently the power system becomes increasingly more difficult to operate, and more insecure with unscheduled power flows and higher losses. With the rapid development of selfcommutated semiconductor devices, it is possible to design power electronic equipments known as the Flexible AC Transmission Systems (FACTS)-devices. The objective of using FACTS devices in power system is to bring systems under control and to transmit power according to the ordered of the control centers. These devices also allow the increasing of the usable transmission capacity to its maximum thermal limits. By using FACTS devices, it is also possible to control the phase angle, firing angle, the voltage magnitude at chosen buses and /or line impedances of a transmission system. Among the FACTS devices, TCSC is one of the most effective measures for increasing the transfer capability of the transmission system, enhancing the stability, increasing voltage profile, reducing transmission losses and ameliorating the dynamic characteristics of power system. However, to achieve the over mentioned benefits, the TCSC should be properly installed in the network with appropriate parameters. In the literature many people proposed different concepts about the placement and sizing of the TCSC,GAPSO and DA Algorithms Hadi Saadat Presented Real and Reactive Power flow equations in polar form by considering two bus power system. A Jacobean matrix is then constructed and Newton Raphson method is used to solve these equations[1].ref.[2]-[6] Papers proposed in literatures for load flow analysis with incorporated FACTS controllers in multimachine power systems from different operating conditions viewpoint. There are different load flow analysis with incorporated FACTS controllers from different operating conditions in multimachine power systems for optimal power flow control. The Newton Raphson Methods have been proposed in literatures includes for different types of Modeling of Series FACTS controllers.sahoo et.al (2007) proposed the basic modeling of the FACTS devices for improving the system performance[7].zhang, X.P et.al explains Jacobian Matrix of Power flow Newton Raphson algorithm and Newton Raphson strong convergence characteristics [8]. About the modeling and selection IJIRT INTERNATIONAL JOURNAL OF INNOVATIVE RESEARCH IN TECHNOLOGY 1620

2 of possible locations for the installation of FACTS devices have been discussed by Gotham.D.J and G.T Heydt (1998) [9].Povh.D(2000) proposed the nice concepts of the modeling of the power systems and the impact of the FACTS devices on the transmission network [10].Modelling of the FACTS devices with various techniques with complete computer programming is proposed by Acha et.al. [11].The impact of multiple compensators in the system was proposed by Radman.G and R.S Raje [12].The important concepts of the power systems with different load flow was proposed by Stagg.G.W et.al(1968) [13]. Tong Zhu and Gamg Haung proposed(1999) the accurate points of the buses which were suitable for the FACTS devices installation [14].P.Kessal H. Glavitsch(1986) proposed increase the transmission capability, improvement of stability by installing FACTS devices in transmission network [15].Hingorani N.G et.al presented about FACTS devices,which are a family of high-speed electronic devices, which can significantly increase the power system performance by delivering or absorbing real and/or reactive power [16]. Hugo Ambriz-Perez et.al presented a novel power flow model for the Thyristor Controlled Series Compensator (TCSC).The model takes the form of a firing angle-dependant, nodal admittance matrix that is then incorporated in an existing Power flow algorithm [17]. Ref [18-20] papers proposed on the placement of the TCSC by using genetic algorithm concepts. Ref [21-22] papers proposed the concept of PSO for placement of both SVC and TCSC. S.Meerjaali (2015) proposed a new approach of optimization by using Dragon fly algorithm [23]. In this paper, the optimal location for placement of FACTS device has been formulated as a problem, and is solved using a new heuristic algorithm called the Dragonfly Algorithm. The Dragonfly Algorithm is used for finding out the optimal locations of Thyristor Controlled Series Compensator (TCSC) devices, to achieve minimum transmission line losses in the system. The Dragonfly Algorithm results are compared with the results of the Genetic Algorithm (GA) and the Partical Swarm Optimization (PSO) techniques. II. POWER FLOW ANALYSIS Load flow studies are important in planning and designing future expansion of power systems. The study gives steady state solutions of the voltages at all the buses, for a particular load condition. Different steady state solutions can be obtained, for different operating conditions, to help in planning, design and operation of the power system. The power mismatch equations P and Q are expanded around a base point (θ(0),v(0)) and, hence, the power flow Newton Raphson algorithm is expressed by the following relationship III. SERIES COMPENSATION Facts controllers can be broadly divided into four categories, which include series controllers, shunt controllers, combined series-series controllers, and combined series-shunt controllers. Their operation and usage are discussed below. A series controller is mainly used to control the series impedance of the line by including the capacitive effect which is contract to the inductive effect of the transmission line. The reduction of the series impedance of the transmission line effects on the voltage drop across the line i.e the voltage at the receiving buses may improve because of the reduction of the series impedance. The overall losses of the system may also reduces with the control of the series impedance of the transmission line. The reactive losses of the system is majorly effect with the change of impedance of the transmission line. With the increase of the voltage profile also it may conclude that the reactive power losses of the system reduces. The basic series compensating device without controlling parameter is series capacitance. The scope of control ability of the series capacitance can be increased by including power semiconductor devices which are called Thyristor controlled series capacitor (TCSC), SSSC and etc. A. Thyristor Controlled Series Capacitor (TCSC) The basic conceptual TCSC [17] module comprises a series capacitor, C, in parallel with a thyristorcontrolled reactor, LS, as shown in Fig. 2. However, a practical TCSC module also includes protective equipment normally installed with series capacitors. A metal-oxide varistor (MOV), essentially a nonlinear resistor, is connected across the series capacitor to prevent the occurrence of high-capacitor IJIRT INTERNATIONAL JOURNAL OF INNOVATIVE RESEARCH IN TECHNOLOGY 1621

3 over-voltages. Not only does the MOV limit the voltage across the capacitor, but it allows the capacitor to remain in circuit even during fault conditions and helps improve the transient stability. The basic module of a TCSC is shown in Fig. 1. It consists of three components: capacitor banks C, bypass inductor L and bidirectional thyristors T1 and T2 Also installed across the capacitor is a circuit breaker, CB, for controlling its insertion in the line. In addition, the CB bypasses the capacitor if severe fault or equipment-malfunction events occur. A currentlimiting inductor, Ld, is incorporated in the circuit to restrict both the magnitude and the frequency of the capacitor current during the capacitor-bypass operation. An actual TCSC system usually comprises a cascaded combination of many such TCSC modules, together with a fixed-series capacitor, CF. This fixed series capacitor is provided primarily to minimize costs. Figure 1 A Basic Module of TCSC B. Operation Of The TCSC (Firing Angle Power Flow Model) TCSC is one of the popular series FACTS controllers. It has been in use for many years to increase line power transfer as well as to enhance system stability. The firing angles of the thyristors are controlled to adjust the TCSC reactance in accordance with a system control algorithm, normally in response to some system parameter variations. IV. FAULT ANALYSIS Improvement of transient stability is an important topic in the modern power system scenario. It is well known the FACTS technology can control voltage magnitude, phase angle and circuit reactance so it is redistributed the load flow and regulate bus voltage bus voltage FACTS device are more effective for improving total transfer capability and transient stability, Fig 4.1 (a) & (b) represent the system with fault conditions. Fault analysis is carried out through both type of fault condition Figure 3: Per unit representation of the system like symmetrical and unsymmetrical fault which provide valuable information about when the fault is cleared after the system subjected to a severe disturbance like sudden application of loads (steel mill), loss of generation (unit trip), loss of large load (line trip), a fault on the system (lightning). The fault and stability analysis are done with TCSC device installed in the SMTB system with 200MVA, 25KV synchronous machine at line 3, the operation and analysis validated through simulation. During the fault period the R.M.S value current flowing through the TCSC device is 160A, the two mode of operation are Capacitor Boost Mode and Inductive Boost Mode, Fig 4.2 (a) & (b) shows the capacitive and inductive boost mode indicating the current direction. This mode allows the TCSC to behave either as a continuously controllable capacitive reactance or as a continuously controllable inductive reactance. It is achieved by varying the thyristor-pair firing angle in an appropriate range. However a smooth transition from the capacitive to inductive mode is not permitted because of the resonant region between the two modes. The firing angles given to switches are between= 690 to 900 and 00 to 470 for Capacitor Boost Mode and Inductive Boost Mode respectively, since the resonance for this TCSC is around 580 firing angle, the operation is prohibited in firingangle range 490 to 690. IJIRT INTERNATIONAL JOURNAL OF INNOVATIVE RESEARCH IN TECHNOLOGY 1622

4 V. CONTROLLER DESIGN OF TCSC Figure 4(a): System representation with fault without TCSC Figure 4.(b): System representing with fault with TCSC (a) (b) Figure 4.2: The fault current flowing through (a) Capacitor boost mode and (b) Inductor boost mode with firing pulse The TCSC increases the power transfer capability of a transmission network in addition several other functions. It provides a rapid Control of the transmission-line series compensation level thus dynamically controlling the power flow in the line. The fuzzy based controller is developed and designed according to the fault current flowing through the transmission lines. The parameters of this controller are adjusted by the different operating mode of TCSC device, the various mode are TCSC bypass mode, capacitive boost mode, Inductive boost mode, Blocked mode, Circuit breaker bypass. The simple one line diagram of TCSC controller is shown in Fig 5.1 with line current and capacitor voltage as input quantity. When TCSC operates in the constant impedance mode it uses voltage and current feedback for calculating the TCSC impedance. The reference impedance indirectly determines the power level; a separate fuzzy controller is used in each operating mode. The capacitive mode also employs a phase lead compensator. Each controller further includes an adaptive control loop to improve performance over a wide operating range. The controller gain scheduling compensates for the gain changes in the system, caused by the variations in the impedance. The firing circuit uses three single-phase PLL units for synchronizations with the line current line current is used for synchronizations, rather than line voltage, since the TCSC voltage can vary widely during the operation. The output of the capacitive and inductive boost mode for the controller and without controller is shown in Fig 5.2 (a) & (b), in which the waveform is compared and indicate that the response of the system with and without TCSC controller for capacitive mode is 0.328s and 0.356s during fault duration and initial response for inductive boost mode is 0.012s and 0.08s respectively VI. STABILITY ANALYSIS The stability analysis are done with and without TCSC device installed in the system at line 3, the transient stability with and without TCSC controller are obtained employing Equal Area Criterion, Fig 6.1 shows the power angle curve which is obtain by calculating the impedance during fault condition, it IJIRT INTERNATIONAL JOURNAL OF INNOVATIVE RESEARCH IN TECHNOLOGY 1623

5 shows that the maximum power output will be obtain when δ=900. For the system to be transiently stable during a disturbance, the rotor angle of the synchronous machine to oscillate around an equilibrium point which is shown in Fig 6.2 which is obtained by the swing equation under sustained fault and when the fault is cleared, which indicate that the 3ø fault with TCSC which attain quickly to an equilibrium point when compared to the system without TCSC device. Fig 6.3 shows the equal area criterion when the system is subjected to a sudden change of power, this indicate that the system with TCSC device provide better power transferability point when compared to the system without TCSC device during the pre-fault condition. The transient stability with and without TCSC controller are obtained employing Equal Area Criterion the critical clearing time without and with TCSC are and respectively, during 3ø fault condition under Capacitor & Inductive Boost Mode. VII. CONCLUSION The fault and stability analysis are done with and without TCSC device installed in the three bus single machine system. The result shows that the total power loss and fault clearing angle is minimize. The fault clearing time when subjected to various fault condition shows that the fault clearing time is reduced and transient stability is improved to attain its stable state after subjected to a fault, when compared to the same system without TCSC fuzzy based device which is validated through Equal Area Criterion REFERENCES [1] Power System Analysis - Hadi Saadat, Tata MC Graw Hill, Edition [2] Abdel-Moamen, M.A. Narayana Prasad Padhy, Power Flow Control and Transmission Loss Minimization Model with TCSC for Practical Power Networks, Power Engineering Society General Meeting, 2003, IEEE, Vol.2, July 2003, pp [3] Venegas T., Fuerte-Esquivel, C.R. Steady- State Modelling Of Thyrister Controlled Series Compensator For Phase Domain Load Flow Analysis Of Electric Network, Electric Utility Deregulation and Restructuring and Power Technologies, Proceedings. DRPT International Conference, 4-7 April 2000 Page(s): [4] Kumar G.R.; Rao, R.K.; Ram, S.S.T., Power Flow Control and Transmission Loss Minimization model with TCSC and SVC for Improving System Stability and Security Industrial and Information Systems, ICIIS IEEE Region 10 and the Third international Conference on 8-10 Dec Page(s):1-5 [5] M.O. Hassan, S. J. Cheng, and Z. A. Zakaria, Steady-state Modeling of Static Synchronous Compensator and Thyristor Controlled Series Compensator for Power Flow Analysis, Information Technology Journal, Vol. 8, Issue 3, 2009, pp J [6] Xiao-Ping Zhang, Advanced Modeling of the Multi control Functional Static Synchronous Series Compensator (SSSC) in Newton Power Flow, Power Systems, IEEE Transactions on Volume 18, Issue 4, Nov Page(s): [7] Sahoo, A.K., S.S. Dash, and T. Thyagarajan Modeling of STATCOM and UPFC for Power System Steady State Operation and Control. IET-UK International Conference on Information and Communication Technology in Electrical Sciences (ICTES 2007). [8] Zhang, X.P., C. Rehtanz, and B. Pal Flexible AC Transmission Systems: Modelling and Control. Springer Verlag: Berlin, Germany [9] Gotham, D.J. and G.T. Heydt Power Flow Control and Power Flow Studies for Systems with FACTS Devices. IEEE Trans. Power Syst. 13(1): [10] Povh, D Modeling of FACTS in Power System Studies. Proc. IEEE Power Eng. Soc. Winter Meeting. 2: [11] Acha, E., C.R. Fuerte-Esquivel, H. Ambriz- Pe rez, and C. Angeles-Camacho FACTS: Modelling and Simulation in Power Networks. John Wiley and Sons: West Sussex, UK. (Power flow has been optimized by placement of the FACTS controllers) [12] Radman, G. and R.S. Raje Power Flow Model/Calculation for Power Systems with Multiple FACTS Controllers. Electric Power Systems Research. 77: IJIRT INTERNATIONAL JOURNAL OF INNOVATIVE RESEARCH IN TECHNOLOGY 1624

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