Analysis and Enhancement of Voltage Stability using Shunt Controlled FACTs Controller

Transcription

1 Volume 1, Issue 2, October-December, 2013, pp , IASTER Online: , Print: Analysis and Enhancement of Voltage Stability using Shunt Controlled FACTs Controller ABSTRACT 1 Kiran Kumar Kuthadi, 2 K. Silpa Devi 1 HOD& Assoc. Professor, Dept. of EEE, SVIST, Tiruvuru, AP 2 ASE, TCS, Hyderabad, Andhra Pradesh, India A critical factor effecting power transmission systems today is power flow control. The increment of load variation in a power transmission system can lead to potential failure on the entire system as the system has to work under a Stressed condition. Thus, the Flexible AC Transmission Systems (FACTS) are integrated in power system to control the power flow in specific lines and improve the security of transmission line. This paper presents an optimal placement of and to determine and locations and control parameters for minimization of transmission loss. Optimal location methods utilize the sensitivity of total real power transmission loss with respect to the control parameters of devices. The location of & is placed based on FVSI. The results have been obtained on IEEE 5 bus and IEEE 14bus test system. Test result shows that both and can determine optimal placement. Keywords: Flexible AC Transmission Systems (FACTS), Static VAR compensator (), Static Synchronous Compensator (), Fast Voltage Stability Index (FVSI). 1. INTRODUCTION Nowadays, the power transmission systems have been changed a lot. The voltage deviation due to load variation and power transfer limitation were observed due to reactive power unbalances has drawn attention to better utilize the existing transmission line. It also causes a higher Impact on power system security and reliability in the world. Hence, the Electrical energy demand increases continuously from time to time. This increase should be monitored or observed because few problems could appear with the power flows through the existing electric transmission networks. If this situation fails to be controlled, some lines located on the particular paths might become overloaded [1]. The Flexible AC transmission systems (FACTS) initiative was originally launched to solve the emerging problems in the late 1980s due to restrictions on the transmission line construction and to facilitate the growing power export/import and wheeling transactions among the utilities. FACTS devices can enhance transmission system control and increase line loading in some cases all the way up to thermal limits thereby without compromising reliability. These devices can be an alternative to reduce the flows in heavily loaded lines, resulting in increased load ability, low system loss, improved stability of the network, reduced cost of production and fulfilled contracture requirement by controlling the power flows in the network, reduce cost of production and fulfilled contracture requirement by controlling the power flows in the network. These capabilities allow transmission system owners and operators to maximize asset utilization and execute additional bulk transfer with immediate bottom-line benefits. FACTS devices provide new control facilities, both in steady state power control and dynamic stability control [2]. 25

2 FACTS devices include static var compensator (), thyristor controlled series compensator (TCSC), unified power flow controller (UPFC) etc. and are connected in shunt with the system to improve voltage profile by injecting or absorbing the reactive power [3, 4]. This paper presents the method of the optimal location utilizes the sensitivity of total real power transmission loss with respect to the control parameters of devices, the new equation of is the sum of reactive power flow that has relationship with bus and the new equation of is sum of real power loss that has relationship with transmission line. The IEEE standard tested power system has been considered as tested system to investigate the effect of considering and on power loss minimization and system stability. 2. MATHEMATICAL MODEL OF FACT S i. Static VAR compensator () The is taken to be a continuous, variable susceptance, which is adjusted in order to achieve a specified voltage magnitude while satisfying constraint conditions. total susceptance model represents a changing susceptance. represents the fundamental frequency equivalent susceptance of all shunt modules making up the. This model is an improved version of models. s normally include a combination of mechanically controlled and thyristor controlled shunt capacitors and reactors. The most popular configuration for continuously controlled s is the combination of either fix capacitor and thyristor controlled reactor [5]. Fig. 1 Basic Structure of As far as steady state analysis is concerned, both configurations can modeled along similar lines, The structure shown in Fig. 1 is used to derive a model that considers the Thyristor Controlled Reactor (TCR) firing angle as state variable. This is a new and more advanced representation than those currently available. The is treated as a generator behind an inductive reactance when the is operating within the limits. The reactance represents the voltage regulation characteristic, i.e., s slope, [4]. The reason for including the voltage current slope in power flow studies is compelling. The slope can be represented by connecting the models to an auxiliary bus coupled to the high voltage bus by an inductive reactance consisting of the transformer reactance and the slope, in per unit (p.u) on the base. A simpler representation assumes that the slope, accounting for voltage regulation is zero. This assumption may be acceptable as long as the is operating within the limits, but may lead to gross errors if the is operating close to its reactive limits. The linearized equation of the is given by the following Eqns. (i) and (ii) where the total susceptance is taken to be the state variable. 26

3 at the end of iteration i, the variable shunt susceptance below up dated according to the Eqn. (ii) given In this paper, the Susceptance model is used for incorporation into an existing power flow algorithm. Here, the state variables are incorporated inside the Jacobian and mismatch equations, leading to very robust iterative solutions. ii. Static Compensator () The consists of one VSC and its associated shunt-connected transformer. It is the static counterpart of the rotating synchronous condenser but it generates or absorbs reactive power at a faster rate because no moving parts are involved. In principle, it performs the same voltage regulation function as the but in a more robust manner because, unlike the, its operation is not impaired by the presence of low voltages as show below Fig.2 and Fig. 3 Fig. 2 Static compensator () system: voltage source converter (VSC) connected to the AC network via a shunt-connected transformer Fig. 3 Static compensator () system: shunt solid-state voltage source 3. FAST VOLTAGE STABILITY INDEX Voltage stability is becoming an increasing source of concern in secure operating of present-day power systems. The problem of voltage instability is mainly considered as the inability of the network to meet the load demand imposed in terms of inadequate reactive power support or active power transmission capability or both. It is mainly concerned with the analysis and the enhancement of steady state voltage stability based on L-index. Consider an -bus system having, generator buses, and the load buses. The transmission system can be represented by using a hybrid representation, by the following set of equations 27

4 It can be seen that when a load bus approaches a steady state voltage collapse situation, the index approaches the numerical value 1.0. Hence for an overall system stability condition, the index evaluated at any of the buses must be less than unity. Thus the index value gives an indication of how far the system is from voltage collapse. The indices for a given load condition are computed for all load buses. The equation for the index for node can be written as, It can be seen that when a load bus approaches a steady state voltage collapse situation, the index approaches the numerical value 1.0. Hence for an overall system voltage stability condition, the index evaluated at any of the buses must be less than unity. Thus the index value gives an indication of how far the system is from voltage collapse. 4. SIMULATION RESULTS For the validation of the proposed FACT s devices, both and have been tested on the following IEEE 5-Bus and IEEE 14-Bus test System. A MATLAB code for both techniques was developed for simulation purpose. 4.1 IEEE 5-Bus Test System i. Location of The solution for optimal location of FACT s devices to minimize the installation cost of FACT s devices and overloads for IEEE 5-bus test system were obtained and discussed in this section. Fig. 3 IEEE 5 Bus Test System without & Voltage stability indices are calculated for the IEEE 5 bus system without any FACTS devices as shown in Fig

5 Fig. 4 IEEE 5 Bus Test System with By considering the Voltage stability index (L j ) value, it is observed that bus Elm is more sensitive towards system security. Therefore bus Elm is more suitable location for to improve power system security/stability. The modified original networks to include as shown in Fig. 4. Table 1: Voltage Stability Index (VSI) Before & After Placement of Name of the Bus FVSI Before FVSI After Lake Main Elm Table 2: Analysis of Voltage magnitudes, Phase Angles for IEEE 5-bus test system with & without Name of the Before Placement of After Placement of Bus VM (p.u) VA (deg) VM(p.u) VA(deg) North South Lake Main Elm Table 3: Analysis of Sending, Receiving Active & for IEEE 5-Bus test system with Branch Sending Active & Receiving Active & MW Mvar MW Mvar

6 ii. Location of The solution for optimal location of FACT s devices to minimize the installation cost of FACT s devices and overloads for IEEE 5-bus test system were obtained and discussed in this section. By considering the Voltage stability index (L j ) value, it is observed that bus Elm is more sensitive towards system security. Therefore bus Elm is more suitable location for to improve power system security/stability as shown in Fig. 5. After placement of voltage stability index is improved and system losses are reduced as shown in Table 4, Table 5 and Table 6. Fig. 5 IEEE 5 Bus Test System with Table 4: FVSI Before & After Placement of Name of the Bus FVSI Before FVSI After Lake Main Elm Table 5: Analysis of Voltage magnitudes, Phase Angles for IEEE 5-bus test system without and with Name of the Before Placement of After Placement of Bus VM (p.u) VA (deg) VM(p.u) VA(deg) North South Lake Main Elm Table 6: Analysis of Sending, Receiving Active & for IEEE 5-Bus test system with Branch Sending Active & Receiving Active & MW Mvar MW Mvar

7 4.2 IEEE 14-Bus Test System i. Location of By considering the Fast Voltage stability index (FL j ) value, it is observed that 14-bus is more sensitive towards system security. Therefore 14-Bus is more suitable location for to improve power system security/stability and improvement of voltage stability as shown in Table 7 and Table 8. Table 7: Analysis Voltage magnitudes, Phase Angles for IEEE 14-bus test system without and with Name of the Bus Before Placement of After Placement of VM (p.u) VA (deg) VM(p.u) VA(deg) Table 8: Analysis of Sending, Receiving Active & for IEEE 14 Bus test system with Branch Sending Active & Receiving Active & MW Mvar MW Mvar

8 ii. Location of The solution for optimal location of FACT s devices to minimize the installation cost of FACT s devices and overloads for IEEE 14-bus test system were obtained and discussed in this section. By considering the Voltage stability index (L j ) value, it is observed that 14-Bus is more sensitive towards system security. Therefore 14-Bus is more suitable location for to improve power system security/stability and improve voltage stability as show in Table 9 and Table 10. Table 9: Analysis of Voltage magnitudes, Phase Angles for IEEE 14-bus test system without and with Name of the Before Placement of After Placement of Bus VM (p.u) VA (deg) VM(p.u) VA(deg) Table 10: Analysis of Sending, Receiving Active & for IEEE 14 Bus test system with Branch Sending Active & Receiving Active & MW Mvar MW Mvar

9 5. CONCLUSION In this paper, a new method for optimal placement and parameters settings of and has been proposed for improving voltage profile in a power system. The proposed approach has been implemented on IEEE 5-bus and IEEE 14-Bus system. The criteria for selection of optimal placement of and were to maintain the voltage profile, minimize the voltage deviations and to reduce the power losses using FVSI. Simulations performed on the test system shows that the optimally placed and maintains the voltage profile, minimizes the deviations and also reduces the real and reactive power losses. REFERENCES [1] A. Kazemi, S. Jamali, M. Habibi and S. Ramezan-Jamaat; Optimal Location of TCSCs in a Power System by Means of Genetic Algorithms Considering Loss Reduction, First International Power and Energy Conference PECon 2006, November 2006, pp [2] L. Gyugyi, C. D. Schauder, S. L. Williams, T. R. Reitman, D. R. Torgerson, and A. Edris, The unified power flow controller: A new approach to power transmission control, IEEETrans. Power Delivery, vol. 10, pp , Apr [3] N.G.Hingorani and L.Gyugyi, Understanding FACTS Concepts and Technology of Flexible AC Transmission Systems. Piscataway: IEEE Press 1999 [4] M.K.Verma, Optimal Placement of for static and Dynamic Voltage Security Enhancement, International Journal of Emerging Electric Power systems,vol. 2,Issue 2, Article 1050,2005. [5] K. P. Wang, J. Yurevich, A. Li, Evolutionary- programming-based load flow algorithm for systems containing unified power flow controllers, IEE Proc.-Gener. Transm.Distribute Vol.150, No. 4, Jul [6] N. G. Hingorani and L. Gyugyi, Understanding FACTS-concepts and technology of flexible AC transmission systems, IEEE press, First Indian Edition, [7] Kesineni Venkateswarlu, Ch. Sai Babu and Kiran Kumar Kuthadi, Improvement of Voltage Stability and Reduce Power Losses by Optimal Placement of UPFC device by using GA and PSO International Journal of Engineering Sciences Research-IJESR, Vol 01, Issue 02, May, 2011 [8] Kiran Kumar Kuthadi and N. Suresh Enhancement of voltage stability through optimal placement of FACT s Controllers in Power Systems American Journal of Sustainable Cities and Society-AJSCS, Issue. 1, Vol. 1, July-2012, pp: [9] Kiran Kumar Kuthadi, M. Suresh Babu and Nagaraju Tella Optimal Location and Parameter Settings of FACT s Devices for Enhancing Power System Stability and Minimization of Power Losses International Journal of Engineering Science and Technology IJEST, Vol. 4 No.06 June 2012, pp [10] Kiran Kumar Kuthadi and M. Suresh Babu, A Modified Particle Swarm optimization technique for solving improvement of voltage stability and reduce power losses using UPFC International Journal of Engineering Research and Applications-IJERA, Vol. 2, Issue 3, May-Jun 2012, pp [11] G. W. Stagg, and A. H. El-Abiad, Computer Methods in Power System Analysis, McGraw-Hill, [12] L. L. Freris, and A. M.Sasson, Investigation on the load flow problem, Proceeding of IEE, Vol. 115, pp ,