Bai bao phan tich etap

International Journal of Physical Sciences Vol 1(2), pp 019-026, June 2013 Available online at http://academeresearchjournals.org/journal/ijps ISSN 2331-1827 ©2013 Academe Research Journals ISSN 2331-1827 Full Length Research Paper Power flow analysis of Rafah governorate distribution network using ETAP software Nadia M Mahdi Electrical Engineering, Technical Administration, GEDCO Company, Gaza, Palestine E-mail: engineer_nadia@yahoo.com Accepted 29 May, 2013 The results of a load flow analysis can be used for operational purposes to evaluate various operating states of an existing system They can also be used in the planning stages to evaluate possible future extension projects This paper discusses the analysis of the power distribution network in Rafah governorate by using ETAP software The aim is to evaluate the technical status of the present medium voltage network (22-kV) The problems and challenges faced by the existing network are analyzed Those problems include the power deficit, high power losses, poor voltage levels and feeders’ overloading Then some solution techniques are suggested considering the system current state and future growth for different scenarios for each problem to obtain a full understanding of the system problems and solutions Key words: Distribution network, power flow analysis, ETAP INTRODUCTION The power-flow analysis of a distribution feeder is similar to that of an interconnected transmission system Typically, before starting the power-flow analysis, the three-phase voltages at the substation and the complex power of all of the loads and the load model must be known A load flow study determines the voltage, current, power and reactive power in various points and branches of the system under simulated conditions of normal operation (William, 2002) Load flow studies are essential in optimizing existing networks, ensuring an economical and efficient distribution of loads, and plan future networks (Jan de Kock and Kobus, 2004) The analysis of a distribution feeder will typically consist of a study of the feeder under normal steady-state operating conditions All of the approximate methods of modeling assume perfectly balanced three-phase systems, balanced three-phase loads, and perfectly transposed three-phase line segments (William, 2002) There are wide ranges of power system analysis programs available in the world market that perform all sorts of electrical analyses They range from basic, commercially packages to large, complex programs developed for a specific customer (Jan de Kock and Kobus, 2004) The software used in this paper is ETAP It is for the design, simulation, and analysis of generation, transmission, and distribution power systems For a power distribution system, it is capable of calculating balanced and unbalanced load-flow This analysis produces detailed reports of system losses, line flows, and voltage at every node The software is capable of recommending optimum capacitor placement, and wire size upgrades (Barn and Jewell, 2005) ETAP Load Flow Analysis module calculates the bus voltages, branch power factors, currents, and power flows throughout the electrical system on both radial and loop systems (ETAP 7.0.0 User Manual, 2009) As a power distribution system load grows, the system power factor usually declines Load growth and a decrease in power factor leads to a number of challenging problems such as: voltage regulation problems, increased system losses, power factor penalties and reduced system capacity (Holm et al., 2010) The distribution network in Rafah experiences many technical problems which need quick solutions The most pressing problems are high power losses and poor voltage especially at the feeder ends To face these challenges, a power flow study for the distribution network must be carried out to find the suitable technical Mahdi 020 Figure The main feeders of Rafah Governorate solutions The main contribution of this paper is that it evaluated the 22-kV network in Rafah and suggests the suitable available technical solutions METHODOLOGY First of all, the MV grid was analyzed using ETAP software in a way such that all problems and deficiencies are investigated clearly and then suitable solutions are tested by simulation about 68800 m feeding 133 of distribution transformers Moreover, the overhead lines cover about 93.8% of the overall length of the network This is because the overhead network is much cheaper than the underground network Most of the 22-kV lines are constructed using ACSR 150/25, ACSR 50/8 and ACSR 95/15 conductors It is important to know that all the previous mentioned data of Rafah network and all work done in this paper represent the network status till the end of 2011 SIMULATION RESULTS AND ANALYSIS Description of the existing network Rafah is a Palestinian city that is located in the south of Gaza Strip on the border between Egypt and Palestine Rafah receives power through four feeders operating at 22 kV as shown in Figure (Gaza Electricity Distribution Corporation [GEDCO], 2010) Three of the feeders are from Egypt and they enter Rafah from the southern side The first feeder has a maximum capacity of MW The second feeder has a maximum capacity of 12 MW, and it’s divided into two feeders The fourth feeder enters Rafah from its eastern side and is owned by the Israeli Electric Company (IEC) All those feeders are governed by Gaza Electric Distribution Corporation (GEDCO), the unique electric distribution company in Gaza Strip MV distribution system is stepped down to 400-V at distribution transformers Then the power is distributed to individual consumers via low voltage distribution networks at 400-V This network serves 22,038 customers which represent 12% of the total customers of GEDCO in year 2011 The MV network falls into two categories: overhead lines and underground cables It is fairly wide spread in Rafah that a total length of Since all feeders in Rafah city are in radial configuration, then each feeder can be analyzed separately The four feeders are simulated in separate projects Their one-line diagrams are drawn and their parameters are entered into ETAP software Then they are exploited in different study cases to evaluate the performance of the grid The feeders are studied assuming balanced load-flow For each study case, the program produces detailed accounts of system losses, line flows, and voltage at every node or bus These detailed reports are used to investigate all problems and deficiencies of the grid Figure depicts a part of the one-line diagram of the IEC feeder The results of load flow module for all feeders are divided into three parts: the first part of the results is concerned with power demand and capacity issues, the second is related to the system losses, while the third part is for voltage magnitude and voltage drop at each node on the feeders It is found that there is a deficit in the available power by about 35% Also the grid suffers from phase load imbalance in the LV networks The line current unbalance Int J Phy Sci 021 Figure One-line diagram of the 1st Egyptian Feeder rate is 7.4% in average to all feeders Moreover, the percentage voltage drop obtained by power flow solution drops below 90% of the nominal voltage in the first one third of the feeders’ length except the second Egyptian feeder The estimated cost of the resulted average energy losses reaches 3.3 million NIS for MWH and million NIS for MVAR in year 2011 It is observable that the percentage of reactive power loss is approximately about 1.6 times more than the active power loss and this is due to the nature of the lines which normally have the value of X/R larger than unity In addition to these problems, the existing grid has a poor lagging power factor in all 22-kV feeders which stay in the range of 81 84% SOLUTION TECHNIQUES After the presentation of all problems and deficiencies of network, the study addresses and suggests solution techniques for those problems Managing the growing power demand In order to satisfy the ever increasing energy demand, several actions have to be implemented These actions have to be carried out in parallel Those actions include the load balance and upgrading of the supplied power according to the actual power demand Also it is important to predict the future growth of the power demand to be taken into account in the upgrade and planning of new projects So the forecasted growth in the power demand was evaluated for the coming ten years from 2012 to 2022 The predicted data were evaluated by excel “FORCAST” function which predicts the future values along a linear trend by using the existing values and they are shown in Figure It is perfectly suitable since the existing data have a linear behavior According to the power demand requirements, it is found that the preferred solution to support the existing load and the future demand growth is to install a new substation in Rafah as an extension to the Egyptian high voltage network The Palestinian Authority of Energy and Natural Resources in Gaza proposed a complete study of a project to install two new substations in Gaza Strip, one of them is intended to extend the Egyptian system and rated at 220/22 kV It will have two of three winding power transformers rated at 60/75 MVA This substation will feed the southern part of Gaza Strip with the required power demand Load balancing A three-phase, four-wire distribution system has been widely used to facilitate low voltage supply to single- Mahdi 022 Figure Growth of peak power demand in summer Figure Power demand in balanced and unbalanced loads phase and three-phase loads This mixed loading in the secondary distribution system may result in serious phase unbalance (Nikhil et al., 2011) By calculations, it is found that the line current unbalance rate in average is 6.37% for the 1st Egyptian feeder, 9.99% for the 2nd Egyptian feeder, 7.21% for the 3rd Egyptian feeder, and 5.76% for the IEC feeder The line current unbalance rate (LCUR) is calculated by equation (1) as shown thus: LCUR%  Max line current deviation from average 100 Average line currents (1) It is noted that the current imbalance exceeds the standard limit of LCUR which equals 3% at maximum Figure indicates the capacity release which can be obtained through balancing loads on the LV network The figure shows that the load balance can release about 7% of the active and reactive powers Voltage improvement Voltage (1) improvement is considered as power quality issue and there are several techniques that can be used to improve the voltage profile of the feeders The voltage profile is enhanced by three techniques: raising the Int J Phy Sci 023 Figure Voltage profiles of the 1st Egyptian Feeder Figure Voltage profiles of the 2nd Egyptian Feeder sending end voltage, changing the tap settings of the distribution transformers, and the last method is accomplished by installation of capacitor banks This improvement is achieved at the expense of higher current and power demand, so this approach must be applied carefully Approach 1: Raising the voltage at the feeder sending-end Approach 2: Adjustment of transformers’ tap setting The most intuitive way in voltage improvement is to raise the voltage at the sending end node Even though the voltage control is done only from the substations, this method is implemented based upon request from technical department of Rafah branch Figures to show the improvement of the voltage profiles considering both the peak and average loading cases Since the IEC feeder suffers more voltage drop than Egyptian feeders due to higher loading and longer length, it is raised to 23 kV as a suitable value for the feeder to operate within the allowable range of voltage in peak and off-peak loading The effect of raising the sending-end voltage is presented in Figure Another method that can be used to enhance the voltage levels along the feeders in the LV side is to readjust the transformers’ tap changer The transformers’ tap changer is on high tension side and can be stepped to +1×2.5% or to -3×2.5% Since the nominal value of the system is 22 kV, then each step can raise or lower the voltage rating by 0.55 kV The tap changer must be adjusted to suitable settings to suit both light and heavy loading cases The 1st Egyptian feeder is tested for this method in summer loading case and the voltage profile along the LV nodes is shown in Figure The tap changers of all transformers connected to LV nodes that experience voltage drop below 90% of the nominal value are adjusted to -3×2.5% position of their tap changers Mahdi 024 Figure Voltage profiles of the 3rd Egyptian Feeder Figure Improvement of voltage profile on IEC feeder Figure Voltage profile variations by adjusting transformer’s tap-changer settings Int J Phy Sci 025 Figure 10 Voltage improvement by capacitors’ placement Table Capacitor banks and power carrying capability Before adding capacitors Sending end PF% 83.39 Average Loading 20.5 kV MW Mvar MW Mvar Loss Loss 6.43 4.25 0.188 0.387 After adding capacitors Sending end PF% 96.17 Approach 3: Installation of capacitor banks Placement of capacitors has been considered mainly to enhance the line voltage levels above 90% of the nominal voltage, power factor correction, and losses reduction Power factor correction permits additional loads to be served by the existing system In case if the transformers or cables get overloaded, improving the power factor will be the most economical way to reduce the current and therefore eliminate overload condition This can be clearly investigated by Equations and (Osama and Ahmad, 2011): PFinitial initial S  PF ×S×S Snew old old new PF final PF final Snew IInew  S new new 3V 3V (2) (3) Average Loading 20.5 kV MW Mvar MW Mvar Loss Loss 6.58 1.87 0.153 0.324 Capacity release (MVA) Peak Load Avg Load 1.044 0.86 Distribution losses in a facility can be reduced by addition of capacitors as clearly investigated by Equation (4) (Osama and Ahmad, 2011):   PF 2  Loss reduction%  1-  initial   ×100   PFfinal   (4) After installing the capacitor banks, the feeder was tested for a combination of different operating scenarios including under voltage of the sending end, overvoltage of the sending end both at minimum and maximum loading cases The load flow simulation indicates (2) that the capacitors operate with its full rating without leading to under voltage or overvoltage conditions and this is what we are searching for Figure 10 shows the enhancement of the voltage profile after installing the capacitor (3) banks regarding different cases of the sending end voltage at the average loading condition (2) (3) Mahdi 026 Not only that the voltage levels are improved, but also the power factor at the sending end is increased from 83.39% to 96.17% Another advantage is that the current loading is decreased; hence the power losses are decreased Moreover, the increased power factor increases the feeder capacity by capacity release which lowers the consumed KWH annually These improvement results are displayed in Table The capacitors’ banks are highly costly, so the project of capacitor placement needs an economic evaluation study The investment cost of this project must be considerable in comparison to profit obtained in the near future It is seen that the payback period is years and in the fifth year, the pure profit starts assuming that the energy price is fixed at 0.28 NIS for KWH and summer loading Conclusion Power flow analysis is an essential step for operational purposes to evaluate various operating states of an existing system Also it is necessary for enhancement and development projects By using ETAP load flow program, it is found that the MV network in Rafah experiences many technical problems including: deficit in the available power, poor power factor, low voltage levels and power losses Based on the obtained results, some technical solutions are suggested to help in the network improvement The solutions are tested by simulation The proposed solutions were suggested considering the financial investment cost and profits such that the solutions are acceptable from the economic view ETAP shows powerful functionalities in load flow analysis field Thus it is strongly recommended to be available for usage in the technical administration of GEDCO REFERENCES Barn L, Jewell W (2005) Review: power system analysis software tools IEEE ETAP 7.0.0 User Manual (2009) Jan de K, Kobus S (2004) Power Distribution for Industry IDC Technologies., p 151 Nikhil G, Anil S, Niazi KR (2011) A Novel Strategy for Phase Balancing in Three-Phase Four-Wire Distribution Systems IEEE Osama A, Ahmad KA (2011) Impact of Power Factor Correction on the Electrical Distribution Network of Kuwait – A Case Study Online Journal on Power and Energy Engineering (OJPEE), 2: Holm RMU, Chopade PV, Prornod J (2010) Optimal Placement of Capacitor for Power Loss Reduction Using ETAP Software ICSES' 10 International Conference on Science Engineering & Spirituality Studies and Documentation Branch in Technical Administration of Gaza Electricity Distribution Corporation GEDCO (2010) William HK (2002) Distribution System Modeling and Analysis CRC Press LLC, 39: 269  ... suitable available technical solutions METHODOLOGY First of all, the MV grid was analyzed using ETAP software in a way such that all problems and deficiencies are investigated clearly and then... simulated in separate projects Their one-line diagrams are drawn and their parameters are entered into ETAP software Then they are exploited in different study cases to evaluate the performance of the... states of an existing system Also it is necessary for enhancement and development projects By using ETAP load flow program, it is found that the MV network in Rafah experiences many technical problems