Performance Analysis on Transmission Line for Improvement of Load Flow

Transcription

1 Performance Analysis on Transmission Line for Improvement of Load Flow YaMinSuHlaing Department of Electrical Power Engineering Mandalay Technological University, Mandalay, Myanmar Aung Zaya Department of Electrical Power Engineering Technological University (Moneywa), Moneywa, Abstract- In this paper, load flow analysis program has been developed using Newton-Raphson algorithm for the solution of power flow problems. The transmission line under unloaded and loaded conditions is compensated using capacitor banks in order to increase line loadability and to get the optimum voltage level at weak voltage buses. The system performance is tested under steady-state condition. The line parameters and performance have been calculated by using several MATLAB functions. This paper investigates and improves the steady state operation of Myanma Power System Network. Keywords- Line Compensation, Load flow, Myanma Power System Network, Newton- Raphson method, steady-state operating condition, I. INTRODUCTION Load flow analysis is the most important and essential approach to investigating problems in power system operating and planning. Based on a specified generating state and transmission network structure, load flow analysis solves the steady operation state with node voltages and branch power flow in the power system. Load flow analysis can provide a balanced steady operation state of the power system, without considering system transient processes. Load flow studies are performed using digital computer simulation. These address operation, planning, running, and development of control strategies. In this paper, it has investigated the power flow over power transmission lines, which is somewhat distinct and a problem by itself. The characteristics and performance of transmission lines can vary over wide limits, mainly dependent on their system. Maintaining an acceptable voltage profile at various buses with varying power flow is a major problem. This paper deal with representation and performance of transmission lines under normal operating conditions. Transmission lines are represented by an equivalent model with appropriate circuit parameters on a perphase basis. The terminal voltage is expressed from one line to neutral, the current for one phase and, thus, the threephase system is reduced to an equivalent single-phase system. The model used to calculate voltages, currents, and power flows depends on the length of the line. The circuit parameters and voltage and current relations can be developed for short, medium and long lines. In this paper, the medium line between two weak voltage buses is compensated. Problems relating to the regulation and losses of lines and their operation under conditions of fixed terminal voltages are considered. The First International Conference on Interdisciplinary Research and Development, 31 May - 1 June 2011, Thailand 69.1

2 Ya Min Su Hlaing and Aung Zaya II. POWER FLOW SOLUTION OF NEWTON-RAPHSON METHOD The Newton-Raphson method is powerful method of solving non-linear algebraic equations. The fundamental Newton-Raphson expression allows for convergence to be assessed by comparing power mismatches (Δs) against a prespecified tolerance rather than voltage comparisons. the shunt capacitance must be considered. Lines above 80km (50miles) and below 250km (150 miles) in length are termed as medium length lines. For medium length lines, half of the shunt capacitance may be considered to be lumped at each end of the line. This is referred to as the nominal model and is shown in Fig.1. Z is the total series impedance of the line and Y is the total shunt admittance of the line given by Under normal conditions, the shunt conductance per unit length, which represents the leakage current over the insulators and due to corona, is negligible and g is assumed to be zero. C is the line to neutral capacitance per km, and l is the line length. The sending end voltage and current for the nominal model are obtained as follows: Equation (3) is in a suitable form for partial differentiation to derive the elements of the Jacobian Fig. 1 Nominal model for medium length From Kirchhoff s law, the current in the series impedance designated by I L is The power mismatch equation is terms It is more efficient in programming A simplified flowchart for Newton- Raphson method is shown in Fig.2. III. MEDIUM LINE MODEL As the length of line increases, the line charging current comes appreciable and In general, ABCD constants are complex and since the model is a symmetrical twoport network, A=D. Special Issue of the International Journal of the Computer, the Internet and Management, Vol. 19 No. SP1, June,

3 Performance Analysis on Transmission Line for Improvement of Load Flow Furthermore,since it is dealing with a linear passive, bilateral twoport network, the determinant of the transmission matrix is unity, The receiving end quantities can be expressed in terms of the sending end quantities by Fig. 2 Flow chart for Newton-Raphson method IV. PERFORMANCE ANALYSIS ON TRANSMISSION LINE FOR IMPORVENEMT OF LOAD FLOW STUDY A configuration of Myanma Power System network is shown in Appendix [MEPE]. A. Myanma Power System Network The Newton-Raphson method is applied to the solution of practical system using the developed software modules. The network of Myanma electric power system is used as the reference case. The reference system is assumed to be operation under balance condition and is represented by a singlephase network. The system network contains 90 buses and 108 branches with impedances specified in per unit on 100MVA system base specified generators, transformers and transmission lines and line to line voltage of 230 kv as bases. B. Simulation Results of Line Performance Program Based on the above procedure, the bus of Lawpita Hydro Power Station (Bus 1) which its voltage is specified as 1.05 pu, is taking as slack bus and the input data for power flow program represents the load and generation of January 8 to 11, Line data, load data, voltage magnitude and reactive power limits for the regulated buses of the power system network are considered on 100MVA, 230kV base. Figs (3, 4, 5 and 6) are test results of simulation for the medium transmission line from Kyunchaung station (bus 18) to Nyaungbin substation (bus 17). According to the results of load flow simulation, the voltage levels in Monywa (bus 16) and Nyaungbingyi (bus 17) substations are lower than specified lower voltage level range 0.95 pu. So the voltage levels in both substations are required to improve for proper system operation. Nyaungbingyi substation (bus 17) is supplied by Kyunchaung Gas Turbine (bus 18). In this paper, the transmission line from bus 18(sending end) to bus 17(receiving end) is compensated to improve voltage level for proper system operation and is the medium transmission line (148.2km and also 132kV line). Table I shows simulation results of line performance program. In this table, required shunt and series capacitor ranges are obtained by simulink. The First International Conference on Interdisciplinary Research and Development, 31 May - 1 June 2011, Thailand 69.3

4 Ya Min Su Hlaing and Aung Zaya Fig.3 is bar chart of voltage level for the uncompensated and uncompensated under full load condition. The voltage profile for the uncompensated and compensated under unloaded condition is described in Fig.4. Fig.5 shows the receiving end power circle diagram. The locus of all points obtained by plotting Q R versus P R for fixed line voltages and varying load angle is a circle known as the receiving end power circle diagram. A family of such circles with fixed receiving end voltage and varying sending end voltage is extremely useful in assessing the performance characteristics of the transmission line. Fig.6 describes the voltage profile for various load conditions for the following case: open - ended line, line terminated in SIL, short-circuit line, and full-load line. Fig. 7 expresses the line loadability and thermal limit curve for medium transmission line. For medium line, the thermal limit dictates the maximum power transfer. TABLE I LINE PERFORMANCE RESULTS Fig. 4 Compensated and Uncompensated voltage profile of open-ended line Fig. 5 Receiving end power circle diagram Fig. 6 Voltage profile for various load conditions Fig. 3 Voltage profile for full load condition Fig. 7 Line loadability curve Special Issue of the International Journal of the Computer, the Internet and Management, Vol. 19 No. SP1, June,

5 Performance Analysis on Transmission Line for Improvement of Load Flow V. CONCLUSIONS By analysing load flow, it can be found that the system has the weak voltage points in some buses.. Bus 16, 17, 85 and 86 have the most weak bus voltages. From this analysis, it can determine voltage levels to get acceptable level, how to implement the voltage control using appropriate methods, to obtain optimum value of the required reactive compensation from simulation. In this paper, the medium transmission line between bus 18 and bus 17 was compensated by using MATLAB program software. The transmission line was compensated with series and shunt capacitors to improve transient and steady-state stability, more economical loading, and minimum voltage dip on load buses and to supply the requisite reactive power to maintain the receiving end voltage at a satisfactory level. The test results with the voltage profile and loading conditions can be seen in Figs (3, 4, 5, 6 and 7). Line performance results of capacitor banks were described in Table I. By compensating the transmission line, it provides the improvement of transmission line efficiency and gives minimum losses and acceptable voltage level. The input data is taken from Load Dispatch Centre Myanma Electric Power Enterprise (MEPE) so that the results can be used effectively in planning and operation of power system in Myanmar. ACKNOWLEDGMENT Firstly, the author would like to thank her parents for their best wish to join the Ph.D course at Mandalay Technological University. The author is deeply grateful to Excellency General Aye Myint, Minister, Ministry of Science and Technology for allowing her to attend the Ph.D Engineering Course at Mandalay Technological University. The author wishes to express her thanks to Dr. Mya Mya Oo, Rector, Mandalay Technological University for her guidance and advice. The author would like to express her gratitude to Dr.Aung Zaya, Head of Department of Electrical Power Engineering and to all her teachers from MTU. The author greatly expresses her thanks to all persons whom will concern to support in preparing this paper. REFERENCES [1] Lynn Powell,, Power System Load Flow Analysis, 1st ed, McGraw-Hill,Inc,2005. [2] S.Elangovan, Advanced Power System Analysis, National University of Singapore, January 7, [3] Xi-Fan Wang, Yonghua Song and Malcolm Irving, Modern Power System Analysis, Xi an Jiaotong University, The University of Liverpool and Brunel University, [4] P.S.R Murthy, Power System Analysis, Formerly Principal O.U. College of Engineering & Dean, Faculty of Engineering,O.U.Hydersbad, [5] James L. Kirtley, Electric Power System, Massachusetts Institute of Technology,USA, [6] G.W.Stagg, El-Abiad and H.Ahmed, Computer Methods in Power System Analysis, McGraw- Hill Book Company, New York, [7] Hadi Saadat Power System Analysis. Singapore: MC Graw-Hill Companies.Inc. [8] J. Arrillage, C. P. Arnold and B.J. Harker Computer Modelling of Electrical Power Systems. John Wiley & Sons Ltd. [9] D.Lukman., Blackburn and T.R, Modified Algorithm of Load Flow Simulation For Loss Minimization In Power System. Proceedings of the Australasian Universities Power Engineering Conference (AUPEC 94), Brisbane, Australia September [10] J. Penny and Lindfield, G Numerical methods using MATLAB. Hertfordshire. Ellis Horwood Limited. The First International Conference on Interdisciplinary Research and Development, 31 May - 1 June 2011, Thailand 69.5

6 Ya Min Su Hlaing and Aung Zaya APPENDIX Fig. A The Configuration of Myanma Power System Network Special Issue of the International Journal of the Computer, the Internet and Management, Vol. 19 No. SP1, June,