THE USE OF POWERWORLD TO CONDUCT LOAD FLOW ANALYSIS AND POWER FACTOR CORRECTION ON STEVENSON’S BUS SYSTEM Cesar Carbajal Andrew Gast Michael Fleck Sara Page Podolsky Dr Fredrick Berry Jared Dinkelaker Kevin Patel Aalap Jha Dr Clifford Grigg Department of Electrical Engineering Rose-Hulman Institute of Technology Terre Haute, IN 47803 Abstract Description of Powerworld Load flow analysis is important for Electrical Engineering students to understand, but the analysis can often be long and tedious One way to either check answers or solve large cases would be to use a software package such as PowerWorld PowerWorld utilizes a highly visual easy-touse graphical interface A student version of this program is available at www.Powerworld.com Since many power companies use such programs, the software also helps students prepare for the real world PowerWorld Simulator is a software package designed to simulate high voltage power systems up to 100,000 busses This package was originally designed for educational purposes; now it is being used in industry as well PowerWorld can be used to give students a comprehensive look at electrical power flow in a transmission grid because it is user-friendly and highly visual Introduction Load-flow analysis can be better understood using computer software packages One of the many load-flow software packages that can be used is PowerWorld This package allows for the easy simulation of bus systems that would take a significant amount of time if done by hand One such system is Stevenson’s bus model This is a relatively small and simple power system Understanding how this system works will assist students in understanding load flow analysis The results of changes to the system can be seen quickly in PowerWorld, further aiding students’ learning process COMPUTERS IN EDUCATION JOURNAL PowerWorld is capable of a wide variety of functions including detailed modeling of phase-shifting transformers, switched shunts, generator reactive capability curves, generator cost curves, load schedules, transaction schedules, dc lines, multi-section lines, and remote bus voltage control The one-line diagrams are animated for the benefit of the users The integrated drawing tools give an easy and fast approach to creating one-line diagrams, circuit diagrams where a single line is shown to represent three phases of a power system PowerWorld uses the Newton-Raphson iteration method, which provides an efficient and accurate solution It also computes the Jacobian (Admittance Matrix), so that the one-line diagram characteristics can be ported to other analysis programs 95 Jacobian Matrices In the manual method of solving multi bus systems, a Jacobian Matrix is created The matrix contains values that depend on the resistances and reactances within the system This matrix is used in combination with voltage and current matrices to iterate to a solution In PowerWorld, students can place busses, generators, transmission lines, etc on a oneline and the program comes up with the Jacobian for the case It then iterates to the solution If, for example, a data value needs to be changed, instead of manually changing the affected values of the Jacobian and then recompleting the long iteration process a student can simply change the data value on the one-line and PowerWorld will find the new solution quickly Table 1- Transmission Line Data Line From To - Birch - Elm - Birch - Pine - Elm - Maple - Maple - Oak - Maple - Pine - Oak - Pine Branch Branch Shunt Resistance (R) Reactance (X) Charging (B) 0.042 0.168 4.1 0.031 0.126 3.1 0.031 0.126 3.1 0.084 0.336 8.1 0.053 0.21 5.1 0.063 0.252 6.1 The students should open a new project file and create a one-line The help tutorial shows how to place busses, generators, lines and loads Students can build a one-line of the bus system using the input data in Tables and 2, and a picture of the one-line in Figure The model they have created can be used to conduct a load flow analysis Table 2- Generator and Load Data Bus Number Bus Name Voltage Load MW Load VAR Gen MW Gen VAR Birch 1.04 65 30 N/A N/A Elm 115 60 N/A N/A Maple 1.02 70 40 180 Oak 70 30 N/A N/A Pine 85 40 N/A N/A Application A one-line diagram of Stevenson’s bus system modeled in PowerWorld is shown in Figure Tables and are the data that corresponds to the system When students solve the case, the one-line becomes animated, giving a graphical representation of the “flowing” load Also, a Power Flow List is available for viewing the complete numerical solution The solutions to the case are in Appendix A Capacitor Study Figure 1- Stevenson’s Bus System 96 At times it is necessary to have a certain minimum per unit voltage level at a particular bus If the Power Flow List shows that a bus is too low, one way of fixing this is to increase the power factor This is achieved by adding a shunt capacitance at that bus Finding the particular value of the capacitor can be difficult by applying the trial and error method, so the easiest and most effective way to determine the capacitance that is needed is by adding a temporary generator at that bus In this case the generator should be added at bus COMPUTERS IN EDUCATION JOURNAL This generator should have a MW output, like a capacitor would have The SetPoint Voltage should be set to the desired per unit voltage at the bus When the load flow analysis is run again, the reactive power of the temporary generator is the value of the capacitor needed to raise the voltage to the desired value The temporary generator can now be deleted and replaced with a capacitor of the value found above, as shown in Figure References William D Stevenson, Jr 1982 Elements of Power Systems Analysis New York: McGraw-Hill PowerWorld Corporation 2004 PowerWorld Corporation Internet Date Accessed 12/12/2004 Biographical Information Cesar Carbajal, Jared Dinkelaker, Andrew Gast, Kevin Patel, Michael Fleck, Aalap Jha, and Sara Page Podolsky, are Electrical Engineering students at Rose-Hulman Institute of Technology who are writing a User’s Manual for PowerWorld as their senior design project Dr Berry, and Dr Grigg are professors at Rose-Hulman who provided guidance throughout the writing process Figure 2- One-line with Capacitor Hand analysis techniques will be very cumbersome and time-consuming PowerWorld produces a fast and accurate solution without requiring iteration by hand Conclusion Students can solve practical power flow systems using PowerWorld’s easy-to-use graphical interface After building the oneline diagram students can conduct load flow analysis Then, they can easily see the results of making changes to the one-line, without going through tedious by-hand calculations The author would be pleased to provide more detail to interested readers and can be conveniently contacted via email at fleckmc@rose-hulman.edu COMPUTERS IN EDUCATION JOURNAL 97 APPENDIX A Solution to Stevenson’s Bus System 98 COMPUTERS IN EDUCATION JOURNAL