SERIES COMPENSATION IN NEPAL ELECTRICITY

SERIES COMPENSATION IN NEPAL ELECTRICITY AUTHORITY GRID DISSERTATION Submitted in partial fulfillment of the requirements of Master of Engineering in Electrical Power Engineering Chandan Kumar Ghosh Department of Electrical and Electronics Engineering School of Engineering Kathmandu University December 2005 SERIES COMPENSATION IN NEPAL ELECTRICITY AUTHORITY GRID DISSERTATION Submitted in partial fulfillment of the requirements of Master of Engineering in Electrical Power Engineeri ng By: Chandan Kumar Ghosh Under supervision of: Lalit Bickram Rana Assistant Professor Department of Electrical and Electronics Engineering School of Engineering Kathmandu University Department of Electrical and Electronics Engineering School of Engineering Kathmandu University December 2005 DEDICATION With a prayer I dedicate this to my mother and my father. ACKNOWLEDGEMENT I would like to thank my family for the full support and their patience to carry out this thesis. I would also like to thank my supervisor, Mr. Lalit Bickram Rana for his guidance and encouragement throughout the project I would like to thank our Head of Department and NORAD program coordinator Dr. Bhupendra Bimal Chettri for his support during our work. I would also like to thank Mr. Roshan Bhattarai and Mr. Brijesh Adhikari without whose patience in searching the reference, this thesis would have been impossible. I would like to thank Mr. Gautam Bajracharya for his ever willingness to help us in his relevant subjects. I would also like to thank Mr. Morten Husom, Powel, Norway who has guided me throughout the thesis with his valuable suggestions. I would also like to thank Mr. Jitendra Mishra, Load Dispatch Centre, NEA, for providing real time data. Lastly I would like to thank all of my batch mates who have helped me all along by sharing their references ABSTRACT It is always better to evenly distribute loads in all the parallel paths of a power system network than to construct new transmission lines to over come congestion in a particular line when existing alternate paths are underutilized. Power Flow in transmission lines does not necessarily follow the law of economics or optimization. FACTS devices are useful to control the flow of power in a transmission network. Series Capacitors are on such FACTS devices which may be used to control and divert power flow in parallel transmission lines to achieve better economic utilization and even loading of transmission lines. Analyzing the NEA System Planning Report 2004 and the Generation and Load Growth in the Western Region of Nepal, there would be a power surplus in the Year 2009 due to excess of generation with respect to the load growth in the region. The surplus power is perceived to be utilized in the Eastern and Central Region of the country. In doing so, one of the parallel paths for evacuation of power shall be overloaded, but the alternate line will be underutilized. There are a few options to mitigate this problem of congestion. Shunt Compensation is first applied and the results are analyzed. It is seen that Shunt Compensation seems useful only to increase voltage profile of the busses and to decrease transmission losses. It has extremely negligible effect on shifting the load from one line to the other alternate lines. Series Compensation is then applied to lightly loaded lines. A m ethodology to choose a critical path is also described. By application of Series Compensation in a lightly loaded line, the load exceeding the limit of the overloaded transmission line is shifted to the lightly loaded line and a FACTS based solution to mitigate congestion is proposed instead of addition of new transmission lines. TABLE OF CONTENTS GLOSSARY OF ABBREVIATIONS ...............................................................................i LIST OF FIGURES ............................................................................................................ii LIST OF TABLES .............................................................................................................iii Chapter 1. INTRODUCTION.........................................................................................1 1.1. 1.2. 1.3. 1.4. 2.1. 2.2. 2.3. 2.4. 2.5. Scope of the Project................................................................................................ 3 Objectives.............................................................................................................. 4 Limitations ............................................................................................................. 5 Organisation Of The Thesis..................................................................................... 5 Series Compensation In Parallel Transmission Lines................................................. 6 Background Of The Model Under Study .................................................................. 7 Upcoming Generation Centres................................................................................. 9 Transmission Line Under Study............................................................................. 11 Load Growth Forecast, Generation and Transmission Plan in The Years 2006-2010 . 12 Chapter 2. INTRODUCTION OF THE SYSTEM UNDER STUDY.........................6 2.5.1. Load Growth Scenario Of The Western Belt.............................................12 2.5.2. Generation Expansion In The Western Region (2006-2010) ....................14 2.5.3. Transmission Planning...............................................................................15 Chapter 3. METHODOLOGY .....................................................................................16 3.1. 3.2. 3.3. 3.4. 4.1. Flow Chart Of The Method ................................................................................... 16 Load Flow Analysis .............................................................................................. 18 Matlab Programs .................................................................................................. 19 Netbas Simulation ................................................................................................ 21 Load Flow Results ................................................................................................ 23 Chapter 4. RESULTS BEFORE COMPENSATION .................................................23 4.1.1. 4.1.2. 4.1.3. 4.1.4. 4.1.5. 4.2. 5.1. 5.2. 5.3. 5.4. Load Flow 2006 .........................................................................................23 Load Flow 2007 .........................................................................................24 Load Flow 2008 .........................................................................................26 Load Flow 2009 .........................................................................................27 Load Flow 2010 .........................................................................................30 Determination Of Optimal Placement Of Capacitors ............................................... 31 Solutions Proposed............................................................................................... 33 Results After Shunt Compensation......................................................................... 34 Results After Application Of Series Capacitor In 2009 ............................................ 36 Load Flow After Series Compensation For 2010..................................................... 38 Chapter 5. RESULTS AFTER COMPENSATION ....................................................33 Chapter 6. DISCUSSIONS ............................................................................................40 6.1. 6.2. 6.3. Effect On Power Loading On Transmission Lines................................................... 40 Effect On Voltage Regulation................................................................................ 41 Effect On Overall Loss.......................................................................................... 43 Chapter 7. CONCLUSION ...........................................................................................44 Chapter 8. SUMMARY AND RECOMMENDATION ..............................................48 APPENDICES A. Bibliography B. Series Compensation Technology C. Power Development Map Of Nepal D. Power Development In The Western Region Of Nepal E. Real Time Load Dispatching During Peak Load : Western Region F. Real Time Load Dispatching During Peak Load: Eastern Region G. Real Time Load Dispatching During Peak Load: Inps Total H. Load Forecast 2006-2010 I. Real Time Node Votages : Ldc Data J. Capacitance Mvar Calculations K. Power Flow Results Using Matlab GLOSSARY OF ABBREVIATIONS Abbreviation DC FACTS INPS KG kV LDC MW MVar NEA SC T/L Full-Form Double Circuit Flexible AC Transmission Systems Integrated Nepal Power System Kali Gandaki Kilovolt Load Dispatch Centre Mega Watts Mega Volt Amperes Nepal Electricity Authority Single Circuit Transmission Line First in Page 44 1 3 7 7 9 6 9 4 44 15 i LIST OF FIGURES Figure No. Caption Page Figure 2-1 Application of FACTS devices in Parallel Transmission Lines ........................7 Figure 2-2 Single Line Diagram of the system from Kaligandaki –A to Bharatpur ............8 Figure 4-1 NetBas Simulation for Year 2007 ....................................................................25 Figure 4-2 NetBas Simulation for Load Flow 2008 ..........................................................27 Figure 4-3 NetBas Simulation for Line Flow 2009 ...........................................................28 Figure 4-4 Line Flow 2010 ................................................................................................30 Figure 5-1 Effect of Placement of Shunt Compensation on Generation by Swing Bus ....34 Figure 5-2 Effect of Placement of Shunt Compensation on Overall Loss.........................34 Figure 5-3 Effect of Shunt Compensation in Voltage Profile............................................35 Figure 5-4 Effect of Shunt Compensation on Line Loading of Bardghat Bharatpur Line 36 Figure 6-1 Increase of power transmission through Butwal Bardghat due to series compensation .............................................................................................................41 Figure 6-2 Damauli Bharatpur Line Loading vs Series Compensation in KG-A Butwal Line ....................................................................................................................................41 Figure 6-3 Effect of Series Compensation on Voltage Regulation....................................42 ii LIST OF TABLES Table No. Table 2-1 Table 2-2 Table 2-3 Table 2-4 Table 2-5 Table 3-1 Table 4-1 Table 4-2 Table 4-3 Table 4-4 Table 6-1 Table 6-2 Table 6-3 Table 6-4 Caption Page Summary of Western Generation Plan connecting busses ........................10 Transmissin Line Data for the region under study.....................................11 Load Forecast in the Western Region........................................................13 Yearly Generation Expansion Plan............................................................14 Transmission Plan : Western Region 132 kV and 220kV .........................15 Flow Chart of the steps of Methodology ...................................................17 Load Flow 2006 Summary.........................................................................24 Load Flow 2007 Summary.........................................................................26 Load Flow 2009 Summary.........................................................................29 Load Flow 2010 Summary.........................................................................31 Effect of Series Compensation in Line Loading from Butwal to Bardghat... ....................................................................................................................41 Effect of Series Compensation in Line Loading from Damauli to Bardghat ....................................................................................................................41 Effect of Series Compensation on Voltage Regulation .............................42 Effect of Series Compensation on Overall Loss ........................................43 iii Chapter 1. INTRODUCTION Transportation of Electrical Power from the site of production to the end users is known as transmission of power. But the transportation of this commodity is different from transportation of other commodities and faces huge challenges. Transmission of Electricity is challenging because it cannot be stored in huge and useful amounts has to be produced and transmitted in real time as per the requirement. Power System Engineers envisage an ideal Power Network like a perfect highway network where there is no traffic congestion. A good highway network is where commutation is achieve in the estimated time and fare due to a very good traffic control system and an optimum usage of all and available alternate highways. It is also a concern that all and not just one of the highways are used to their absolute capacity. However, in a Power System, power between the nodes flows according to the relation between the sending and receiving end voltages, the sine of the angle between them and the inverse of the reactance of the line connecting the nodes. In a given branch of a power network, the magnitude of power flow strictly adheres to the nature of the transmission line and its characteristic s. Due to deregulation of energy different tariff structures in a similar consumer group with different service facilities, mode of payment and conditions of contract is available in many countries. For a country like Nepal, utilities can reap better tariffs from power sensitive customers by provid ing dedicated feeders with contracted reliable supply conditions such as low priority constraints during load shedding, etc. Even such schemes would require Power Diversion through selected corridors which can only be conceived 1 by use of FACTS devices and could be a first step towards a contracted reliable service to its consumer against a better tariff conditions. In a deregulated market, the transmission grid has a responsibility to only transmit power from one power house to a wholesaler of electricity at a cost of wheeling as per the contracts between the wholesalers and the power generators. Timely financing on additional transmission lines may not always be possible where as the generation growth could exceed transmission limits of a part of a network. Unforeseen power demand increase and demand surges may result to unanticipated power congestion in certain transmission lines and underutilization of other transmission lines. The main objective of a Transmission System Operator, however, is to optimize the use of its transmission lines, and avoid uneconomical use of power transmission and congestion reflecting poor profitability. In order to optimize the use of the transmission lines, and thus to wisely trap wheeling contracts, to take advantage of the diversity of loads, changes in peak demand due to weather and time differences, the availability of different generation reserves in various geographic regions, power-sharing arrangements among utilities, shifts i fuel prices, regulatory changes, and other discrepancies, the n control of power flow in a grid is essential. This can be only achieved by proper use of FACTS devices. FACTS technology is being promoted as a means to extend the capacity of existing power transmission networks to their limits without having to add new transmission lines. The importance of FACTS devices is becoming increasingly interesting to the power industry as it is difficult to add new transmission lines due to environmental and right-of-way restrictions. The other potential advantages of FACTS lie in their ability to improve damping and to control the flow of power through selected corridors in a network. 2 1.1. Scope of the Project The scope of this thesis is to study the effect of one of the FACTS devices, the series capacitor on the behavior of a power network. Analysis of other FACTS devices except shunt capacitor is not covered in this topic. To explain the effect of Series Compensation, only a part of the Integrated Nepal Power System (INPS) is chosen. The section under study is the section in the Western sector from Bharatpur to Lamahi and Kaligandaki. The effect of load growth in this sector and the generation scenario is studied to calculate the surplus area from this section of INPS. Hence the upcoming power plants in other part of Nepal and load growth is not relevant. To have a realistic situation, a period of coming five years is chosen for the study of upcoming power plants and their likely effect of congestion in the transmission line. Situation beyond 2010 is not considered. The major reference for the generation plan and the load forecast is the system planning report 2004 [2]. Any further information beyond this report is not considered. Out of the various effects of Series Compensation in parallel lines of a power network, the effect of Series Compensation in stability enhancement and its quantitative analysis is also beyond the scope of the thesis. Series Compensation and other FACTS devices have a significant role in optimal power flow in transmission lines. However, the economic analysis of Series Compensation, optimal allocation and sizing of reactive power sources to improve the economic benefits, is also not considered in this thesis. 3 1.2. Objectives The objectives of the study are as follows: • To study the possibility of series compensation as a technology practically useful and to do a research on the references of this technology and its benefits • To find out various advantages of series compensation technology in power systems • To study the effect of series compensation on loading of power in a parallel transmission line • • To study the effect of series compensation on voltage regulation of the network To study the effect of series compensation on overall loss of a network In order to achieve these objectives, the western section of the line of INPS is being chosen as a model. To the best of accuracy from the given data of Reference [2], the power system is modeled and power flow is simulated using MatLab and NetBas. The following are the secondary objective of the study • To study the Transmission Generation and Expansion Plan of Nepal Electricity Authority • • • To study the congestion (if any) due to improper planning (if any) To find viable FACTS based Series Compensation solution for the above To recommend NEA the use of Series Compensation and its benefits. 4 1.3. Limitations The Thesis covers analysis of only the effect of Series and Shunt Compensation in the network. Hence effects of other FACTS devices are not covered in this thesis. The thesis covers analysis of upcoming power plants and load growth in the Western part of Nepal and the generation and load growth in other parts of Nepal is not considered. The effect of Series Compensation on stability enhancement and its quantitative analysis of the stability issue is not a part of this thesis. Similarly, economic analysis of Series Compensation, optimal allocation and sizing of other reactive power sources is also not considered. 1.4. Organisation Of The Thesis The thesis has the introductory part, in which Series Compensation as a viable Technology is being introduced. In order to explain the effect of Series Compensation, a practically interesting site, the Western Grid is being chosen, and hence an introduction of the network under study is an important part of the thesis. Literature Search section deals with the basic academic background and the papers referred to carry out this thesis. There are a few methodologies exercised in this thesis to reach at the results. There is a separated chapter for the analysis of the results and summary and recommendations. 5 Chapter 2. Introduction of the System under Study This chapter is to introduce the subject under consideration. The introduction has two parts. The first part introduces the Series Compensation Technology and the second part introduces the system and the model on which the Series Compensation is applied. The reference of the first part is ABB brochures, Reference [13] and articles. The reference of the second part is the NEA System Planning Report [2]. 2.1. Series Compensation In Parallel Transmission Lines A simple meshed network is shown to illustrate a hypothetical power flow situations. Here generators at A and B feed a 3000-MW load at C via transmission lines AB, with continuous power rating of1000 BC (250 MW) and AC (2000 MW). At the impedances shown, BC will be overloaded, carrying 1600 MW. Series three-phase thyristor-controlled capacitors in line AC [top, right], reactors (inductors) in line BC [bottom, left1 or phase shifters in line AC [bottom, right] can restore the flow in BC to no more than its rated 250 MW. The reference for this topic is [23] 6 Figure 2-1 Application of FACTS devices in Parallel Transmission Lines 2.2. Background Of The Model Under Study The Integrated Nepal Power System (INPS) is divided into mainly three sections, the Eastern Region, the Central Region and the Western Region. The Eastern Section starts from East of Hetauda to Dhalkebar and to Anarmani. The Central Section starts from Bharatpur to Kathamandu Valley and to Khimti. It extends to Birgunj from Hetauda. The Western Section starts from Bharatpur to Lamahi and Mahendranagar, along with Kaligandaki. The section under study is the parallel 132 kV transmission line starting from the country’s largest Power Station Kaligandaki-A (Bus No. 1) (KG-A) to Bharatpur (Load Bus No. 4) The first section of the parallel path is via Lekhnath (Bus No. 2) and Damauli (Bus No. 3). The second section of the parallel path is via Butwal(Bus No. 6) and Bardghat (Load Bus No. 5). Modi (Bus No. 9) Power Station is connected to Pokhara (Load Bus No. 8) which is connected to Lekhnath. Similarly, Jhimruk (Bus No. 12) Power Station is connected to 7 Lamahi (Load Bus No. 11) which is connected to Shivpur (Load Bus No. 10) and to Butwal. Gandak (Bus No. 7) Power Station is connected to Bardghat. Figure 2-2 Single Line Diagram of the system from Kaligandaki –A to Bharatpur The reasons behind choosing the above section is as the model for analysis is as follows: • Among the various advantages and applications of the use of Series Compensation, load diversion in a Parallel Path to reduced and shift load from a heavily loaded section to a lightly loaded section is the objective of the thesis. The objective requires a realistic Transmission Line Model and the above choice is ideal. • According to the Generation Expansion Plan of NEA, there are many power plants coming in this region and thus the study of congestion would be realistic. • The section is limited to Bharatpur as it is the exit of the surplus power from the Power Stations situated in the Western Region. • The region also has Kaligandaki-A which is the Swing Bus of INPS. 8 There are some approximations and simplifications in this model. All transmission lines below 132 kV and their loads are concentrated to 132 kV Substations. Loads on the 132 kV transmission line west from Lamahi ha ve been lumped to the load at Lamahi. Loads on the 132 kV transmission line East to Bharatpur, i.e. Hetauda and other cities are consolidated at Bharatpur. Though the total capacity of Marshyangdi power house is 75 MW, referring to real time LDC data [4] only 25 to 27 MW of power is considered to contribute to the power to Eastern Nepal via Bharatpur, and the rest of the power from this station is considered for supply to the Central Region (not shown in Fig. 2.1). The reason behind connecting Mashyangdi Power Station to the Model is to get a dedicated Active Power of 25 MW to the Eastern region and also get Reactive Power, as per the capacity of the Power Station. To exemplify, the model could get a reactive power of -30 MVar to + 45 MVar. Thus, this makes the model more realistic. 2.3. Upcoming Generation Centres Upper Marshyangdi (50 MW) is the other major power station apart from Middle Marshyangdi (70 MW) to be connected at Damauli in the coming five years. Hewa Khola (10 MW) and Khudi and Nyadi are other small hydropower stations to be connected at Damauli. Hence, Damauli will be a major Power Centre with a generation of around 138 MW is planned to be connected at Damauli Bus. The other major Power Centre anticipated in this region would be Modi, where Upper Modi-A (IPP-40 MW), Upper Modi (14 MW) and Lower Modi (19 MW) will be connected to Modi Bus, totaling a generation of 89 MW lumped from Modi in the coming five years. 9 Kaligandaki is the Swing Bus (Bus Code 1) in the model. Smaller Power Stations with capacity less than 10 MW are considered PQ Bus (Bus Code 0). The rest of the power stations are PQ buses, (Bus Code 2). Thus it is seen that important generating buses in the coming five years would be Damauli and Modi. Table 2-1 Summary of Western Generation Plan connecting busses Max MVAR 86.40 6.00 6.00 30.00 2.10 42.00 2.70 82.80 3.00 3.00 4.20 6.00 25.20 11.40 8.40 8.40 53.40 18.00 18.00 6.12 16.26 282.18 Min MVAR -57.60 -4.00 -4.00 -20.00 -1.40 -28.00 -1.80 -55.20 -2.00 -2.00 -2.80 -4.00 -16.80 -7.60 -5.60 -5.60 -35.60 -12.00 -12.00 -4.08 -10.84 -188.12 Bus Code Gen MW 144.00 10.00 2 0 10.00 10.00 50.00 3.50 70.00 4.50 3 2 138.00 5.00 6 Gandak* Pokhara Total Raughat Upper Modi -A Lower Modi Upper Modi Modi* Modi Total Chameliya Lamahi Total Jhimruk* Marsyangdi* TOTAL 11 12 13 0 2 2 9 8 0 10.00 42.00 19.00 14.00 14.00 89.00 30.00 30.00 10.20 27.10 470.30 7 2 5.00 7.00 Bus Connection Kaligandaki* Madi Lekhnath Total Hewa Khola Upper Marsyandi Khudi Mid Marsyangdi Nyadi Damauli Total Dharma Khola Butwal Total 1 Bus No 1 10 2.4. Transmission Line Under Study The transmission line under study consists of the main two parallel lines: • • Kaligandaki-A – Lekhnath - Damauli- Bharatpur 132 kV transmission line and Kaligandaki-A – Butwal – Bardghat - Bharatpur 132 kV transmission line. The others are 132 kV transmission lines from other power stations to either of the above nodes. The synopsis of the transmission line and their capacities are as listed in Table 2.2 Tabl e 2-2 Transmissin Line Data for the region under study Kaligandaki Lekhnath Damauli Bharatpur Bardghat Kaligandaki Bardghat Lekhnath Pokhara Butwal Shivpur Lamahi Bharatpur 1 2 3 4 5 1 5 2 8 6 10 11 4 Lekhnath Damauli Bharatpur Bardghat Butwal Butwal Gandak Pokhara Modi Shivpur Lamahi Jhimruk Marsyangdi 2 3 4 5 6 6 7 8 9 10 11 12 13 Duck Wolf Wolf Panther Bear Duck Panther Wolf Bear Bear Bear Otter Duck 1 1 1 1 1 2 1 1 1 1 1 1 1 0.0949 0.1844 0.1844 0.1375 0.1102 0.0949 0.1375 0.1844 0.1102 0.1102 0.1102 0.3434 0.0949 24.1 18.1 18.1 21 22.9 24.1 21 18.1 22.9 22.9 22.9 12.6 24.1 48 39 39 70 43 58 14 7 37 61 51 50 25 Km Name Bus of Name Bus of No. of ckt 180 103 103 123 142 180 123 103 142 142 142 67 180 The only double circuit transmission line in 132 kV in this region is from Kaligandaki to Butwal with a length of 59 kms. The capacity of the line from Damauli to Bardghat is 103 MVA and the capacity of the line from Butwal to Bardghat to Bharatpur is 123 MVA. These two parallel lines are the backbone of the power evacuation transmission line from Line Capacity MVA 11 Resistance per km Overall Diameter Conductor Bus No Bus No the Western Region to the East and central region. The loading of these two lines under the generation plan has been modeled for each year and the effect of series compensation is being studied in the thesis. The simplified network is chosen only as an example to demonstrate how power systems behave under generation plans. As transmission of electricity differs from transportation of any typical commodity by some inherent aspects such as production needs to match the consumption in real time, system control is not an easy task. The complexion is further added because the electricity flows do not usually follow the economic law. This aspect is normally observed when transmission systems are included in, for instance, an economic dispatch problem. One way to minimize the operational costs caused by an overloaded transmission system is through the installation of Flexible AC Transmission System (FACTS) devices in the system. This thesis shows how they are able to change power flows by modifying the network parameters. This solution can also change the overall costs of the system and impact on transmission pricing. 2.5. Load Growth Forecast, Generation and Transmission Plan in The Years 2006-2010 The section gives the picture of the load in the Western Part of Nepal in the coming five years, and the amount of power available for Eastern Part of Nepal from the power stations in the Western Part. 2.5.1. Load Growth Scenario Of The Western Belt Referring to the System Planning report and its Load Growth Forecast, the estimated load of the substations of the Western Region is presented in Table 4.1 Here, the load from Lamahi to the Wetsern parts of Nepal in the radial 132 kV Transmission Line is being 12 lumped at Lamahi **, and thus it accounts for the loads of Kohalpur Lamki Attaria and MahendraNagar as well. Thus the remaining power surplus after consumption of these subsations are to be supplied to the Eastern and Central Region of the country from Bharatpur*. Table 2-3 Load Forecast in the Western Region 2006 Bus Code Load MW Bus No 2007 Load MW 2008 Load MW 2009 Load MW 2010 Load MW 7.04 10.56 240.00 29.42 269.42 8.00 30.00 57.13 87.13 24.64 3.51 40.00 5.16 459.46 Lekhnath Damauli Eastern of Bharatpur* Bharatpur Self Bharatpur Total Bardghat Butwal Western** Self Dharma Khola Butwal Pokhara Shivpur Lamahi Jhimruk 2 3 0 2 4.93 7.39 50.00 23.46 5.36 8.04 140.00 25.52 165.52 6.43 5.87 8.80 150.00 27.93 177.93 7.04 6.42 9.64 180.00 26.85 206.85 7.50 4 5 2 0 73.46 5.91 10.00 30.79 15.00 43.50 20.00 47.60 25.00 52.14 6 8 10 11 12 0 0 0 2 40.79 17.24 2.46 40.00 3.61 199.79 58.50 18.76 2.67 45.00 3.93 318.21 67.60 20.53 2.93 40.00 4.30 339.00 77.14 22.48 3.20 40.00 4.71 381.94 13 2.5.2. Generation Expansion In The Western Region (2006-2010) Referring to [2], it seems that most of the power stations of Nepal is to be developed in the Western Part of Nepal. The Generation contribution of power houses in the Western Region at present is 211 MW whereas it is expected to double in fiver years time. Where as the Load in the region will most likely not grow in the same proportion. Table 2-4 Yearly Generation Expansion Plan 2006 Code Gen MW Bus No Bus 2007 Gen MW 2008 Gen MW 2009 Gen MW 2010 Gen MW 3.50 70.00 4.50 138.00 5.00 5.00 7.00 Kaligandaki Madi Lekhnath Hewa Khola Upper Marsyangdi Khudi Mid Marsyangdi Nyadi Damauli Dharma Khola Butwal Gandak 1 1 144.00 144.00 144.00 10.00 144.00 10.00 10.00 144.00 10.00 10.00 10.00 50.00 2 0 0.00 0.00 10.00 3.50 70.00 4.50 3 2 4.50 5.00 6 7 2 5.00 7.00 4.50 78.00 5.00 5.00 7.00 3.50 70.00 4.50 78.00 5.00 5.00 7.00 3.50 70.00 4.50 78.00 5.00 5.00 7.00 Pokhara Raughat Modi Upper Modi-A Lower Modi Upper Modi Modi Modi Total Lamahi Chameliya Jhimruk Marsyangdi TOTAL 8 0 10.00 42.00 19.00 14.00 14.00 9 11 12 13 0 2 2 14.00 0.00 10.20 27.10 211.80 14.00 28.00 0.00 10.20 27.10 299.30 14.00 14.00 28.00 0.00 10.20 27.10 309.30 14.00 14.00 89.00 30.00 10.20 27.10 400.30 42.00 19.00 14.00 14.00 89.00 30.00 10.20 27.10 470.30 14 Considering the load growth and the generation expansion, there will be power surplus in the Western Region, and since a few power plants are proposed in the Eastern Region, there will be power deficit in the Eastern Region of Nepal. Thus power evacuation from Western Region to the Eastern Region must be undertaken and Transmission Planning must be carried out taking the above into consideration. 2.5.3. Transmission Planning Referring to the System Planning Study 2004 [2], we see a few transmission line commissioning in the coming five years in the western region: Table 2-5 Transmission Plan : Western Region 132 kV and 220kV Year Addition of Committed transmission line 2004-2006 Butwal Bardghat 132 kV second circuit not completed, expected to be completed in year 2006 2007 220 kV Khimti – Dhalkebar T/L charged at 132 kV 2008 220 kV Hetauda Bardghat T/L 2009 – 2010 Nil 15 Chapter 3. Methodology This chapter explains the methodologies used to carry out this project. The first part explains the total process in a flow chart format and the major tasks or steps of the thesis. The other parts of the chapter are basically the elaboration of the two kinds of analysis done in the thesis. 3.1. Flow Chart Of The Method To compute the optimal level of series compensation required in the Transmission Lines, the following methodologies have been used. 1. The first and foremost step is to prepare a simplified parallel transmission network of the Western Zone from Kaligandaki to Bharatpur via Butwal and via Damauli. The load of the substations from Lamahi to Mahendranagar is lumped at Lamhi. The available surplus power at Bharatpur is being computed for utilization (evacuation) in the Central and Eastern region of our country. The simplified model considers around 25 MW of power from Marshyangdi Power House to contribute to the Eastern Power Requirement. However, there is no limitation for VAR and reactive power can flow from the power house to Bharatpur as per its capacity. The next step is to compute the Yearly Load Forecast of the substations in the Western Belt from year 2006 to year 2010 for the Western Grid (From Bharatpur to Lamhi Section) of the INPS as per the load forecast and integrated generation plan of NEA. 16 Table 3-1 Flow Chart of the steps of Methodology NO YES The System Planning Department of NEA, Transmission Planning Study, 2004 [2] is the reference for the data. The load flow is tested for deviations between real time figures and obtained flow results to ensure the accuracy of the model. 17 The generation plan for the coming five years (2006-2010) considering small as well as large upcoming power plants in the Western Region is analysed for each year. The yearly power flow in each transmission line is computed using total Forecasted Load of the substations in the Western Grid (Bharatpur to the Western part of Nepal) . 2. Load Flow of each year is computed analytically using analytical methods [1]. Manual calculation of Load Flow is simplified using MatLAB programming. 3. A simulation of the the Load Flow of the Transmission Line for each year from 2006 to 2010 is also done using the NetBas software. This is to ensure the results from the analytical method The basis of performance of Load Flow is the analytical method of computing Load Flow using the Newton Raphson Method and the Gauss Siedel Method [1]. There are 13 number of busses in the transmission line between Butwal and Bharatpur in the simplified Transmission Line. There are two paths for the power flowing from Kaligandaki Power House to Bharatpur. The first way of power flow is via Butwal and Bardghat. The second way of power flow is via Lekhnath (New Pokhara) Damauli. 3.2. Load Flow Analysis The first step towards a Load Flow Analysis is the formation of the bus admittance matrix. The line parameters are being calculated on the basis of Transmission Line data of the Transmission Planning Study 2004 of NEA [2]. The Line Parameter calculations are shown in Appendix A. 18 The next step is to assign the category of different busses as Slack or Swing bus, Load Bus and the Generation Bus and corresponding bus code (second column of the matrix busdata) 1, 0 or 2 respectively. Considering the next five year generation plan of NEA, the categories of some of the busses would change from Load to Generation bus as the power plants are gradually connected to the system. Load flow is done using Gause Siedel method or Newton Raphson method, whichever is suitable and convergent. 3.3. Matlab Programs There is an intensive use of MatLab programming to perform the Load Flow Analysis of the system. The Load Flow is being performed by a M- file powerflow.m. The scope of research of this thesis is the effect of series compensation of the Transmission Line Section between Kaligandaki Butwal Bardghat Bharatpur. Hence this M- file asks the user to specify the level of series compensation and number of circuit for analysis in the Butwal Bardhat Bharatpur Section of the Transmission Line. On the basis of the specified number of circuits and the degree of series compensation, the bus data consisting of per unit value of the resistance, impedance and susceptance of each section of the line is computed. The powerflow.m Mat file requires two matrices as its basic inputs. They are the matrix busdata and the matrix linedata. There are a few M-files which are being directly used from [1]. lfybus.m Mat-file obtains the Bus Admittance Matrix for power flow solution using the seed matrix busdata. However, there are six columns of the matrix busdata which are to be completed as per the transmission line. They are : 19 [ From Bus No. Reactance To Bus No. per unit Line Resistance perunit Line per unit Line Suceptance Transformer Tap Changing Ratio ] The number of Rows of the matrix busdata is equal to the number of sections of the transmission lines. The raw data from the field is put first in a basic data matrix bd whose first and second column are the Bus no From and Bus no To. The third fourth and fifth input are the conductor characteristics of the line, viz., resistance of the conductor per km, the overall cross sectional area of the conductor and the Length of the section. The matrix bd is used to compute the matrix busdata using the formulas to compute the line inductance and line capacitance. The process is simplified by the use of an Mat- file gmd which computes the GMD Geometric Mean Distance between the phases, GMRL and GMR C. They are then used to compute the Line Inductance and Line Capacitance. The base voltage chosen is 132 kV and the base MVA chosen is 100 MVA, and the Zbase is then calculated to compute the per unit value of the line parameters. The powerflow.m utilizes the matrix lfybus created using busdata. lfnewton or lfgauss can be used for loadflow. The final loadflow result is stored in the busoutfinal matrix. This is the basic methodology of the research. Load flow is being carried out for load and generation plan of each year starting from 2006 till 2010. Based on this load growth outlook, generation expansion and various transmission planning scenarios and contingencies, transmission lines cascading over load conditions are closely monitored and the location and amount of series compensation to increase power transfer capability is determined using [3]. 20 After locating the line to be series compensated, load flow is again carried out but, attempting generation redispatch possibilities [3]. If the generation redispatch is still unable to relieve the flow limit, the transmission plan [2] is referred to check if there are any other transmission lines or circuits added to the overloaded transmission line. Load flow is again computed using the new line data and generation redispatch is again attempted. If the Operational Limit Boundary (OLB) has again reached the cascading overload, the line is identified as the critical transmission line whose flow limit causes the start of the cascading overloads. Different series compensation levels are chosen such as 25%, 50% and 75% and applied to the lightly loaded transmission line. Load flow is again performed using the compensated line parameters. The effects are recorded as Results and are further analysed. 3.4. Netbas Simulation NetBas simulation is a cross check of the analytical method. Analysis via NetBas thus ascertains the load flow is correct. To get a clear picture of the cascading overload, considering the load growth, generation expansion plan, and transmission planning, NetBAS simulation is performed on the simplified transmission line from Kaligandaki to Bharatpur via Butwal and via Damauli. The results are tabulated and analysed. However there are certain limitations using NetBas. The conductor data inbuilt in the software are used for simulation, which can affect the overall loss of the simulation. Else, NetBas gives a visual display of the Load Flow. 21 It may be difficult to get an exact load flow results using both MatLAB powerflow and NetBAS simulation, even if the line parameters are well matched. The following methodology for MatLAB powerflow as well as NetBAS simulation is useful. 1. Choose one of the power houses as the swing bus. Choose the rest of the busses as load busses for the first attempt. 2. Carry a load flow and find the bus voltages. Use the bus voltages and optimize the power flow by gradually changing each bus to generation bus where generators are connected. Repeat load flow using acceptable generation bus voltages and optimize. 3. Final load flow is a result of number of iterations and matching of generation bus voltages with real time load data obtained from NEA Load Dispatch Centre [4]. 22 Chapter 4. RESULTS BEFORE COMPENSATION This chapter deals with the results obtained from the methodology used in Chapter 4 to compute Load Flow for different conditions. It is seen that when power stations are gradually added a few sections become overloaded and congested. The critical line where cascading overload occurs is determined and the location of the line to be Series Compensated is ascertained. The chapter has its conclusive section where the results after series compensation and the analysis there after is presented. 4.1. Load Flow Results The yearly load flow results are as follows: 4.1.1. Load Flow 2006 There is real time data availabe from the Load Dispatch Centre NEA (Appendix ) to cross check the load flow analyis.In this year, the following results are worth noting from the analytical load flow: A. Total Load available at Bharatpur is about 70 MW of which 20 MW will be consumed locally and the rest 50 MW will be available to the Eastern Belt of Nepal B. Contribution from Marshyangdi power house is about 25 MW which means contribution from the power houses of the Western Region is 45 MW C. Power Flowing from Damauli to Bharatpur (Bus No. 3 to 4) is around 30 MW where as Power Flowing from Bardghat to Bharatpur (Bus No. 5 to 4) is 15 MW 23 D. There is not much congestion in any of the lines so far. Details are provided in the Appendix Table 4-1 Load Flow 2006 Summary Angle Degree Voltage Mag Bus Voltage 138.6 129.3851 134.6664 Load Mvar Bus Code Load MW Gen MW Kaligandaki Bharatpur Butwal Total 1 4 6 1 0 0 1.0500 0.9802 1.0202 0.00 -5.03 -2.92 0.00 73.46 40.79 199.79 0.00 28.79 15.99 78.31 136.26 0.00 5.00 204.06 0.00 0.00 0.00 Line Flow and Losses Line from 1 3 4 5 6 -to 6 4 Power at bus & line flow MW 93.61 30.45 -73.46 Mvar 25.062 8.466 -28.79 8.719 8.761 MVA 96.914 31.61 78.90 18.789 21.575 -- Line loss-MW 1.371 0.419 Mvar -1.046 -0.963 4 5 16.644 19.716 0.212 0.127 -2.869 -1.805 Comparing with the NETBAS results, we find that the results have insignificant error. 4.1.2. Load Flow 2007 In the year 2007, there would be two more power plants in the Western Transmission Line. As per the Generation Expansion Plan, Middle Masyangdi with a capacity or 70 MW and Upper Modi with a capacity of 14 MW would be connected at Damauli and Modi InjMVAr 0 0 0 Bus No Qmax 24 respectively, along with a small HP Khudi with a capacity of 3.5 MW. Hence a surplus of 65 MW would be available from these new power plants (considering the load growth in the Western Region also) for evacuation to the Eastern Region via Bharatpur. Hence, the amount of power that can be drawn at Bharatpur to the Eastern Region would be around 115 MW (considering consumption at Bharatpur). Figure 4-1 NetBas Simulation for Year 2007 Similarly we can observe the following in this year: A. Total power available at Bharatpur is around 135 MW, out of which around 25 MW will be required for its consumption at Bharatpur and 110 MW will be available for power evacuation in the Eastern Zone. B. Contribution from Marshyangdi Power House is kept at around 25 MW, and hence, 85 MW of power will be available from the Western Sector. 25 C. Around 90 MW of power will flowing from Damauli where as only 20 MW of power is flowing from Bardghat. Table 4-2 Load Flow 2007 Summary Angle Degree Voltage Mag Bus Voltage 138.6 132.132 123.3514 132.2508 124.4404 Mvar 3.690 7.076 -1.992 Load Mvar Bus Code Kaligandaki Damauli Bharatpur Butwal Marsyangdi Total 1 3 4 6 13 1 2 0 0 0 1.0500 1.0010 0.9345 1.0019 0.9427 0.00 -1.68 -5.99 -3.74 -5.08 0.00 8.04 135.00 58.50 0.00 287.69 0.00 3.15 52.91 22.93 0.00 112.76 141.81 78.00 0.00 5.00 27.10 297.11 69.99 21.48 0.00 0.00 7.00 110.88 Summary of Line Flow and Losses --Line-from 1 3 4 5 4 to 6 4 Power at bus & line flow MW 121.795 93.091 -135.000 19.403 Mvar 49.650 33.073 -52.910 17.285 -MVA 131.526 98.792 144.998 25.986 MW 2.528 4.047 0.427 4.1.3. Load Flow 2008 By this time, according to the Transmission planning, second circuit of the 132 kV line from Butwal to Bardhat would have been erected. The only addition of power plant in the Western Region is Madi with a capacity of 10 MW, to be connected at Lekhnath. Thus the load flow in line sections do not change much from the previous year and the line between Gen Mvar Line loss-- Load MW Gen MW Bus No 26 Damauli and Bharatpur nears its capacity with a line loading of around 90%. The following points are worth noting in this year: Figure 4-2 NetBas Simulation for Load Flow 2008 • There was some decrease in the power ava ilability through Bharatpur to the Eastern Region because only one power station with a capacity of 10 MW was added in the Western Region, where as the load growth was more than the added capacity in the region. • Around 90 MW flowed from Damauli to Bharatpur where as only 15 MW flowed from Bardghat to Bharapur. • Line voltage regulation is better due to improved generation dispatch Details are presented in the Appendix. 4.1.4. Load Flow 2009 There will be around 90 MW of addition of Generation capacity in the Western Region in this year. Around 20 plus 40 MW will be added at Modi and 30 MW Chameliya will be 27 added through Attaria eventually to Lamahi. However, there is nothing proposed for any Transmission Line addition or alternatives. Figure 4-3 NetBas Simulation for Line Flow 2009 We must note the following in this power flow: A. In order to maintain acceptable voltage limits in load busses, the swing bus (Kaligandaki A) has to be operated at a higher voltage. B. 190 MW of power is theoretically available at Bharatpur. Around 28 MW will be consumed locally, and hence we will have 160 MW of surplus energy for the Eastern Region. C. 130 MW tries to flow from Damauli to Bharatpur where as 40 MW or more tries to flow from Bardgha t. Marshyangdi still continues to generate around 25 MW for Bharatpur. Thus it is quite evident that the Damauli Bharapur circuit 28 will be overloaded in this year, and all the available power cannot be utilized in the eastern belt. The summary of the load flow for this year is as follows: Table 4-3 Load Flow 2009 Summary Angle Degree Voltage Mag Bus Voltage 141.9 139.656 135.3 122.8946 134.3232 142.56 131.93 125.272 Load Mvar Bus Code Kaligandaki Lekhnath Damauli Bharatpur Butwal Modi Lamahi Marsyangdi Total 1 2 3 4 6 9 11 13 1 0 0 0 0 2 0 0 1.0750 1.0580 1.0250 0.9310 1.0176 1.0800 0.9995 0.9490 0.00 0.43 -2.42 -8.27 -4.24 4.67 -7.21 -7.52 0.00 6.42 9.64 190.00 77.14 0.00 55.00 0.00 380.09 0.00 2.52 3.78 86.22 30.23 0.00 21.56 0.00 160.73 140.98 10.00 78.00 0.00 5.00 89.00 30.00 27.10 397.28 79.45 4.00 46.60 0.00 0.00 1.49 14.00 23.75 175.31 Line Flow and Losses --Line-from 3 4 5 6 4 5 Total loss to 4 Power at bus & line flow MW 131.262 -190.000 41.043 45.932 Mvar 51.037 -86.220 27.194 25.985 MVA 140.835 208.648 49.234 52.773 --Line loss-MW 7.833 Mvar 15.339 1.398 0.382 17.170 Gen Mvar Load MW Gen MW Bus No 0.731 -3.223 14.590 29 4.1.5. Load Flow 2010 As per the generation plan [2], this year will see more power plants in the Western Region. Hewa Khola worth 10 MW and Upper Marsyangdi worth 50 MW will be connected at Damauli. And there is no sign of addition of transmission line in this section [2] Figure 4-4 Line Flow 2010 The conclusions for the above results are much the same: A. 235 MW of power could be available at Bharatpur for need of the Eastern Region provided we have adequate and well designed transmission lines. 180 MW of power tends to flow from Damauli to Bharatpur, where as only 40 MW tends to flow from Butwal to Bharatpur via Bardghat. 30 B. To maintain an acceptable voltage limit in the load buses, the generation of Kaligandaki is raised to 143 kV. Table 4-4 Load Flow 2010 Summary Angle Degree Voltage Mag Bus Voltage 143.22 141.9528 139.8012 123.4543 134.6928 132.264 142.1772 143.22 130.9097 132.1056 125.8224 Load Mvar Bus Code Kaligandaki Lekhnath Damauli Bharatpur Butwal Gandak Pokhara Modi Lamahi Jhimruk Marsyangdi Total 1 2 3 4 6 7 8 9 11 12 13 1 0 2 0 0 0 0 2 0 0 0 1.0850 1.0754 1.0591 0.9353 1.0204 1.0020 1.0771 1.0850 0.9917 1.0008 0.9532 0.00 1.29 -1.27 -9.02 -4.74 -5.75 1.95 5.70 -8.43 -8.27 -8.27 0.00 7.04 10.56 235.00 87.13 4.00 24.64 0.00 60.00 5.16 0.00 445.04 0.00 2.76 4.14 92.10 34.15 1.57 9.66 0.00 23.52 2.02 0.00 174.44 142.83 10.00 138.00 0.00 5.00 7.00 10.00 89.00 30.00 10.20 27.10 469.13 86.16 4.00 80.90 0.00 0.00 1.79 4.00 -12.90 14.00 4.23 23.75 205.94 Summary of Line Flow and Losses --Line-from 3 4 5 6 5 Total loss 6 4 to Power at bus & line flow MW 180.685 -235.000 -47.803 48.204 -28.253 25.071 54.334 Mvar MVA 71.458 -92.100 194.302 252.403 55.528 0.402 0.402 -3.182 24.098 31.517 -3.182 MW --Line loss-Mvar 13.948 28.673 4.2. Determination Of Optimal Placement Of Capacitors We see from the load flow of 2009, the line between Damauli and Bharatpur will be overloaded to its capacity if we intend to evacuate all the available power from Modi and Gen Mvar Load MW Gen MW Bus No 31 Kaligandaki. The methodology suggested by [3] now is to open the overloaded line between Damauli and Bharatpur. A load flow is carried out with the line between Damauli and Kaligandaki opened. The load flow did not come to a solution even after 500 iterations. Generation redispatch is tried but, without any success! The paper [3] then suggests that this is identified as the critical line and series capacitance be applied to other transmission lines. In our case, we have the other alternate transmission line as the Butwal Bardghat Bharatpur Section. 32 Chapter 5. RESULTS AFTER COMPENSATION 5.1. Solutions Proposed There are three solutions to mitigate the problem of congestion in the NEA transmission lines. Firstly, the generation redispatch can allow less generation or power flow to the Western Loads. But if the objective is to attend the power deficit in the Eastern Region, then such a solution would not be useful. The second option is to construct new transmission lines. There are two further options for constructing new transmission lines from Damauli to Bharatpur. One way is to add the second circuit from Damauli to Bharatpur, in which case, the line capacity increases from 103 MVA to 206 MVA. This option can solve problem till the year 2009, and cannot solve the problem for the year 2010. The power flow solutions for the year 2010 suggest that the double circuit line will be overloaded in that year. The other way is to construct transmission line from Damauli to Marshyangd i and plan ahead to add another circuit line from Marshyangdi to Kathamandu Valley. But this option will help to evacuated power to the Central region, precisely Kathmandu Valley and not the eastern region, and its analysis is not considered in this thesis. The third option is to implement FACTS devices. Application of Shunt Compensation is first analyzed and then application of Series Compensation is analyzed after it. 33 5.2. Results After Shunt Compensation 50 Mvar of Shunt compensation is first applied at various nodes. The chosen nodes are Bharatpur, Bardghat and Butwal. The results are as follows: Generation by swing bus Kaligandaki Overall Line Loss 142.5 142 141.5 141 140.5 140 139.5 139 138.5 138 No Co mp Bu tw al Ba rdg ha t Bh ara tpu r 22 Generation by swing bus Kaligandaki 18 MW 14 10 No Co m p Bu tw al Ba rdg ha t Bh ara tpu r MW Overall Line Loss Places of Shunt Compensation Places of Shunt Compensation Figure 0-1 Effect of Placement of Shunt Compensation on Generation by Swing Bus Figure 0-2 Effect of Placement of Shunt Compensation on Overall Loss From the results attached in the Appendix, it is seen that the over line loss is minimum when the capacitor is placed at Bharatpur. This is natural as the compensation is applied at the load centre which reduces the reactive power demand from the generating power stations, decreasing the overall line loss. Figure shows that for exactly similar load conditions, the overall loss is least when shunt compensation is applied at Bharatpur and the swing bus Kaligandaki saves 3 MW of power. 34 Voltage Profile 1.15 1.1 Voltage in PU 1.05 No Comp Butwal Bardghat Bharatpur 1 0.95 0.9 1 2 3 4 5 6 7 Bus No 8 9 10 11 12 13 Figure 0-3 Effect of Shunt Compensation in Voltage Profile The application of shunt compensation results in an improved voltage profile in almost all of the nodes, irrespective of the placement of the shunt compensation. However, placement of shunt compensation at Bharatpur produces best voltage profile improvent. But Shunt Compensation fails to address the issue of power diversion from a heavily loaded transmission line to a lightly loaded transmission line when we analyse the power flow in the network after application of Shunt Compensation. 35 Line Loading Bardghat Bharatpur 39 38.5 38 MW Line Loading Bardghat Bharatpur 37.5 37 36.5 No Comp Butwal Bardghat Bharatpur Place of Compensation Figure 0-4 Effect of Shunt Compensation on Line Loading of Bardghat Bharatpur Line Thus we can conclude by the application of Shunt Compensation, we can improve the System Loss, Power Factor and the Voltage Profile but we cannot change the Line Loading. It is thus advisable to look into other other FACTS devices for a solution to divert power. 5.3. 2009 Results After Application Of Series Capacitor In Series Compensation is not required for load flows till 2008, as the line is not overloaded till then. But lines get overloaded after 2009. Thus SERIES CAPACITOR 36 COMPENSATION is then applied at 25%, 50% and 75% of the total line reactance of the section. Load Flow is again carried out, and results are as follows: When compensation is applied at Kaligandaki Butwal Bardghat Bharatpur Section, the following is the summary of the results obtained: I) 25% compensation at Kaligandaki Butwal Section Line Flow and Losses --Line-- Power at bus & line flow from 3 4 5 6 4 5 to 4 MW 126.937 190.000 45.112 50.062 Mvar 48.877 -86.220 28.786 27.696 --Line loss-MVA 136.022 208.648 53.513 57.213 1.621 0.440 1.336 -3.093 MW 7.307 Mvar 14.180 II) 50% compensation at Kaligandaki Butwal Section Line Flow and Losses --Line-from 3 4 5 6 Power at bus & line flow to 4 MW 122.537 Mvar 48.151 --Line loss-- Transformer MVA 131.658 208.648 56.958 60.857 1.799 0.488 1.791 -3.010 MW 6.782 Mvar 13.005 -190.000 -86.220 4 5 49.164 54.168 28.759 27.739 III) 75% compensation at Kaligandaki Butwal Section Line Flow and Losses --Line-from 3 4 5 6 4 5 to 4 Power at bus & line flow MW 117.980 Mvar 47.75 MVA 127.280 208.648 60.537 64.639 --Line loss-MW 6.280 Mvar 11.881 -190.000 -86.22 53.411 58.465 28.49 27.57 1.993 0.539 2.295 -2.907 IV) 75% compensation at Kaligandaki Butwal Bardghat Bharatpur Section Line Flow and Losses --Line-- Power at bus & line flow --Line loss-- 37 from 3 4 5 6 to 4 MW 93.451 Mvar 40.978 MVA 102.040 208.648 81.570 86.272 MW 3.968 Mvar 6.746 -190.000 -86.220 4 5 77.063 82.639 26.740 24.773 3.544 0.951 -0.983 -3.954 5.4. Load Flow After Series Compensation For 2010 This year, it is expected that a second circuit will be strung between Damauli and Bharatpur and the capacity of the line from Damauli to Bharatpur will be 206 MVA (Wolf). Thus, the line loading without compensation is as follows: Line Flow and Losses --Line-from 3 4 5 6 4 5 to 4 Power at bus & line flow MW 180.685 Mvar 71.458 MVA 194.302 MW --Line loss-Mvar 28.673 13.948 -235.000 -92.100 252.403 42.810 48.204 26.036 25.071 50.106 54.334 1.435 0.402 0.814 -3.182 The summary of the results is as follows: A. The power available at Bharatpur is 235 MW, of which around 25 MW will be fed by Marshayngdi and the rest 210 MW will be evacuated from the other power plants of the West. Considering the load flow, the line between Damauli and Bharatpur will be loaded to 194 MVA even after compensating the Butwal Bardghat section by 75%. 38 B. The line loading of the Butwal Bharatpur section will be only 54 MVA, which is still an underutilization of the double circuit addition between Butwal and Bardghat. C. But there is no alternate to series compensating the Kaligandaki Butwal Bardghat Section. Hence, it is again advisable to series c ompensate the Kaligandaki Butwal Bardghat Bharatpur Section of 132 kV Transmission Line, so that there is atleast equal loading in the two sections. 39 Chapter 6. Discussions The following are the major effects of Series Compensation in the Kali Gandaki Butwal Bardghat Bharatpur 132 kV Transmission Line: Series Compensation reduces transmission reactances at power frequency, which brings a number of benefits for the user of the grid, all contributing to an increase of the power transmission capability of new as well as existing transmission lines [5]. The benefits are: • • • • An improvement in system stability Improvement of voltage regulation and reactive power balance Improved load sharing between parallel lines In many cases, a reduction in transmission losses. Definitely the results are in conformity with the above, except for point number one which is beyond the scope of this study. 6.1. Effect On Power Loading On Transmission Lines As per the generation plan and considering the load growth, in the year 2009, we can have more than 170 MW of power surplus from the western region and can be used to feed the increasing demand of the central and eastern region. However, in doing so, the transmission line between Damauli and Bharatpur (Wolf Conductor) will be highly overloaded from its capacity of a mere 103 MVA. Thus, stringing of a second circuit (if the towers are so designed) or an additional transmission line construction would be an option between Damauli and Bharatpur. But, by using series capacitor the power excess to the capacity of the line can be diverted through another parallel path, i.e., through Kaligandaki 40 Butwal and Bardghat. The following shows the effect of Series Capacitance on the power flow through Kaligandaki Butwal Bardghat Bharatpur Section: Table 0-1 Effect of Series Compensation in Line Loading from Butwal to Bardghat Line Flow from Butwal to Bardghat MW 0% compensation 25% compensation 50% compensation 75% compensation 75% compensation 45.932 50.062 54.168 58.465 82.639 Mvar 25.985 27.692 27.739 27.57 24.773 MVA 52.773 57.213 60.857 64.639 86.272 Loss 0.382 0.44 0.488 0.539 0.951 Figure 0-1 Increase of power transmission through Butwal Bardghat due to series compensation Table 0-2 Effect of Series Compensation in Line Loading from Damauli to Bardghat Line Flow from Damauli to Bardghat MW 0% compensation 25% compensation 50% compensation 75% compensation 75% compensationr 131.262 126.937 122.537 117.98 93.451 Mvar 51.037 48.877 48 47.759 40.978 MVA 140.000 136.022 131.658 127.280 102.040 Loss 7.883 7.307 6.782 6.28 3.968 Figure 0-2 Damauli Bharatpur Line Loading vs Series Compensation in KG-A Butwal Line 6.2. Effect On Voltage Regulation One of the major advantages, Series Compensation in one section of a transmission line affects the voltage regulation of the entire network positively. Thus series compensation 41 can also improve voltage profile like shunt compensation and there is no disadvantage of using series compensation for improved voltage profile. This is demonstrated very well through the following results: Table 0-3 Effect of Series Compensation on Voltage Regulation Voltages pu values at Bharatpur 0% compensation between Kaligandaki A and Butwal 25% compensation between Kaligandaki A and Butwal 50% compensation between Kaligandaki A and Butwal 75% compensation between Kaligandaki A and Butwal 75% compensation between Kaligandaki A and Butwal and Bardghat to Bharatpur 0.974 1.026 1.04 1.045 0.949 1.023 1.044 1.035 0.942 1.014 1.035 1.03 0.9340 1.0060 1.0260 1.025 0.9310 0.9980 1.0180 1.025 Bardghat Butwal Damauli Figure 0-3 Effect of Series Compensation on Voltage Regulation 42 6.3. Effect On Overall Loss The effect of Series Compensation on overall loss of a transmission network can be variable and depends on specific case. In the case of this thesis, power is diverted from a transmission line with WOLF conductor (Damauli Bharatpur Section) to a double circuit more efficient DUCK conductor (Kaligandaki Butwal Section). It is seen that the increase in transmission loss due to increased lenght of the alternate path is however neutralised by the better efficiency of this alternate path. Hence, there is no significant impact of Series Compensation on the overall loss. Table 0-4 Effect of Series Compensation on Overall Loss Total System Loss MW 0% compensation between 17.17 14.59 397.279 Mvar Generation Percentage Kaligandaki A and Butwal 25% compensation between Kaligandaki A and Butwal 50% compensation between Kaligandaki A and Butwal 75% compensation between Kaligandaki A and Butwal 75% compensation between Kaligandaki A and Butwal and Bardghat to Bharatpur 16.885 10.554 396.997 0.042532 16.49 5.844 396.586 0.04158 16.177 1.143 396.267 0.040823 16.67 -7.157 396.829 0.042008 Table 6.1 Effect of Series Compensation on overall loss 43 Chapter 7. CONCLUSION The voltage profile and transmission system Loss can be improved by application of Shunt Compensation. But the objective to divert power through a lternate lightly loaded lines from a heavily loaded line is not achievable using Shunt Compensation. By reducing the reactance of line in a section of Transmission Line, there is an immense possibility to utilize other lightly loaded sections of transmission line to the thermal limit and control its loading. As suggested by many in the References, Series Compensation is one of the most viable technologies, which has many other advantages apart from improving the load sharing capability of parallel transmission lines and improving voltage regulation and in most cases improving loss as well. Construction of Transmission Lines requires long term planning which is capital intensive. Improper planning of Transmission may lead to deadlock in power evacuation in a transmission lines. Transmission lines planning must be coordinated by Load Growth Forecasts in load centres of a country and the upcoming generation plan. Through this study it is seen that the Generation Plan is considering many power plants to come up in the Western Nepal. The Load Growth forecast is however indicating that the load growth in Eastern Nepal has a higher rate than in Western Nepal. Generation Plans are encouraging power plants in the Western Region considering the economics of power production. But it is certain the power produced by these plants in the Western Nepal would be more than the demand of the Western Loads, and thus there would be surplus power which can be utilized in the other part of the country. 44 However, in the year 2009, The re would be surplus power of about around 170 MW from the power plants of the Western Nepal, which has to be evacuated to Eastern Nepal. There are two transmission lines which will be utilized to do the evacuation. The first is the Kaligandaki Lekhnath Damauli Bharatpur 132 kV transmission line, with a capacity of 103 MVA, which will evacuate power from Middle Marshyangdi and Modi. The second path is the Kaligandaki (DC 132 kV 180MVA) Butwal (SC 132kV 142 MVA)Bardghat (SC 132kV 123 MVA) Bharatpur Transmission Line. When 170 MW of power would be surplus, the load flow suggests that 130 MVA tries to flow from Damauli where as only 35 MVA will flow from Butwal Bardghat. It is quite evident that the Damauli Bharatpur transmission line with a capacity of 103 MVA will be highly overloaded, and so all the power cannot be transferred to Bharatpur. Though the transmission plan report only suggests a second circuit addition in Butwal Bardghat section, this analysis shows that it will not have such an economic benefit as addition of second circuit between Damali and Bharatpur or Damauli Mashayngdi Bharatpur section. We hope that the completion of Middle Marsyhangdi (70 MW) power plant to be connected at Dumre will be in close co-ordination with the necessary transmission plans. However, in case of delay in transmission line construction or coordination mismatch, due to unavailability of funds etc, for such a capital intensive project, this study suggests the use of Series Capacitors in different sections of the Transmission Lines as one of the viable alternatives to the congestion problem and improper load sharing between the two transmission lines. 45 With 75% Series Compensation in the Kaligandaki Butwal Bardghat Bharatpur section, Line flow in Damauli Bharatpur section can be reduced to 102 MVA where as the Line loading in Kaligandaki Bhardghat Bharatpur section can be increased to 86 MVA. This provides a worth while solution to the congestion problem in many ways. • Installation of Series Capacitors does not require huge commissioning periods • Extremely environment friendly as social and environmental mitigation problems of constructing or adding transmission lines is completely bypassed. • • • Usually costs 10-20% of the total cost of a new transmission line Simple commissioning procedures Power flow in a network is dynamic. The power flow changes after an addition of a new power plant. Thus, constructed but underutilized transmission lines cannot be dismantled and shifted to new areas to mitigate congestion. But FACTS devices can be decomissioned and shifted to areas requiring greater attention due to congestion. Hence, this could be a temporary solution to the congestion problem as a construction of other transmission line is inevitable for future growing generations. However, installation of series capacitor will enhance the stability of power system. And if there are FACTS devices already installed in the system, power loadability can be controlled through them. The prime objective of Series Compensation in this study was to shift the power from overloaded line to under utilized line. However, by series compensating Kaligandaki Butwal Bharatpur Section, there is also positive effect on Voltage Regulation. Usually, NEA grid operator has difficulty maintaining the voltage at Bharatpur, which is always 46 quite below acceptable limit in the peak load condition. By series compensating the lines, we see that the voltage at Bharatpur has been significantly increased from 0.93 pu to 0.97 pu. This is a priceless achievement and reduces the cost of other power voltage stabilizers used for improvement of voltages in certain sections. In the year 2010, atleast 210 to 230 MW will be surplus and available to the Eastern region. There seems no alternative than to string another circuit between Damauli and Bharatpur, and to raise the capacity of the section to 206 MVA. Performing Load Flow for this situation, we find that 205 MVA would flow from Damauli to Bharatpur. It means that the Damauli Bharatpur section will again near to its overloading capacity. Thus, series compensation in the Kaligandaki Butwal Bharatpur section in the Year 2009 would certainly be helpful for equal sharing of power between the two lines. 47 Chapter 8. Summary and Recommendation Summarizing the thesis and as suggested by Reference [18], power flow in a transmission network can be controlled by using FACTS devices, which in normal cases would take arbitrary paths according to the line parameters. The use of one such FACTS devices, Series Compensation is being successfully demonstrated in this thesis. This study is carried out in a Transmission Line Section of the Western Grid of Nepal, to which a majority of future generation plants shall be connected. This study assesses the transmission congestion problem could arise by unplanned generatio n without supportive and coordinated proper transmission line planning and development approach. For the surplus power evacuation form the Western Region to Load Centres in Eastern and Central region of Nepal, the study focuses on best utilization of the existing transmission lines, and prolongs the construction of unnecessary Transmission Lines. According to the study, transmission congestion was inevitable in the year 2009, and there are two solutions for this problem. First is a cost intensive solution to add a double circuit line in the congested section which too would solve the problem for only one year. The second is to Series Compensate under utilized transmission line so that the power flow from the congested line is shifted to the under utilized line. This prolongs the construction of new lines, and may be a good solution in certain circumstances. Even if a second circuit is added to the congested section in Year 2009, and no compensation is applied elsewhere in the transmission line, by the Year 2010, the newly - 48 - strengthened transmission line (Damauli Bharatpur) too seems to get overloaded. Hence, the two choices are summarized as follows: 1. Add the second circuit in Damauli Bharatpur section in Year 2009 and series compensate the other section in Year 2010, or 2. Series compensate in Year 2009 in KG-Butwal-Bharatpur 132 kV line, and add second circuit in Damauli Bardghat Section in year 2010. The second circuit addition could be done in few ways. First is to simply add second circuit in Damali Bharapur section. This will allow the surplus power to flow to Eastern Region more than the central region. Second is to connect Damauli to Marshayngdi, which would allow power flow to Central Region and Eastern Region. Third is to connect Damauli to Marshyangdi and add a second circuit from Marshyangdi to Bharatpur. This will allow the surplus power flow to Central as well as Eastern Region. Whatever the case may be for double circuiting the section from Damauli to Bharatpur, this addition of transmission line in no effect enhances better utilization of the KG-A Butwal Bharatpur Transmission Line. Hence, series compensation of the KG-A Butwal Bharatpur Transmission Line must be encouraged, to increase utilization of this line - 49 -