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Personal ComputerAREAWhat is the sum of all the losses? ___________Bus 102 Voltage: Per Unit: ________ kV: ________Post-Contingency Bus 102 Voltage: Per Unit: ________Load at Bus 102: ________ MW ________ MVarSystem Intact12 LineHow much of the transaction actually “loops” throughECE 4501 Power Systems Laboratory Manual Rev 1.111.0 POWER SYSTEM SIMULATION11.1 POWERFLOW MODELING USING PowerWorld Simulator 13.011.1.1 OBJECTIVETo use and understand a powerflow simulation and gain understanding of the impact of various power system components, such as generators, transmission lines, transformers and shunts, on system voltage levels.11.1.2 DISCUSSIONA power system is designed and operated to maintain certain minimum requirements of reliability and safety. Such requirements include maintaining system voltage levels such that the steady state voltage at any point on the system lies within +/- 5% of its nominal value. In other words, if the nominal voltage on the high voltage side of a power transformer were 100 kV, acceptable voltage would range from 95 kV to 105 kV. The system is designed to maintain that range even if a piece of equipment, such as a transmission line, is taken out of service. The loss of one piece of equipment is called a single contingency or just a contingency. Voltage values as low as 90% of nominal may be acceptable under emergency conditions where the loss of multiple pieces of equipment has weakened the system beyond its design constraints.Another requirement is operating the system in a manner that will avoid the overloading of any transmission line for an extended period of time (10 minutes or more). Transmission lines are rated in megavolt-amperes of capacity. The ratings are based on the maximum conductor temperature at which the line is designed to operate. Conductor temperatures are a function of the thermal heating experienced by the line’s conductors when carrying electric load. Since the conductors have significant thermal mass, there is a time delay between a sudden change in thermal heating (such as from an overcurrent on the conductors) and the subsequent rise in temperature. This window of time allows the operators of a power system to make changes to the grid in order to relieve the problem. As a general guideline, a transmissionline can withstand a 115% overload for 10 minutes without exceeding design temperature.This laboratory exercise is designed to use the PowerWorld Simulator 13.0 to demonstrate methods for relieving transmission overloads, regulating system voltage and conducting power transactions between interconnected systems.Page 1ECE 4501 Power Systems Laboratory Manual Rev 1.1Power system simulators are mathematical models of the electric system. They use an iterative method to simultaneously solve a large matrix of complex numbers, which numerically represent the power system for a set of initial conditions. They are often accompanied by a graphical interface which allow the user to ‘see’ the numerical results they produce.11.1.3 INSTRUMENTS AND COMPONENTSPowerWorld Simulator, Version 13.0Saved Case 4501-11.pwbPersonal Computer11.1.4 PROCEDURESaved Case 4501-11 contains an interconnected power system with three independent areas (consider them to be three different electric utilities). The three areas contain buses (substations), units (generators) and lines (transmission lines). All three areas also contain loads (a load represents the electric power delivered to customers from a given substation) at various buses. Transmission lines that run from one area to another are called tie linesor just ties.Area 1: Buses: 101, 102, 103, 104 Generators: ONE Tie Lines: 2 with Area 2, 1 with Area 3Area 2: Buses: 201, 202, 203 Generators: ONE Tie lines: 2 with Area 1, 2 with Area 3Area 3: Buses: 301, 302, 303 Generators: TWO Tie Lines: 1 with Area 1, 2 with Area 2Bus 302 is the “swing generator” or “slack bus” for the entire system. {Simulators need one bus (with a generator) at which the error of each iteration in a solution can be added to make the equations balance}1. Start PowerWorld and open case 4501-11.pwb.2. Using the mouse, click on Case Information from the top menu bar and then select Areas. As stated previously, this case consists of three Page 2ECE 4501 Power Systems Laboratory Manual Rev 1.1areas, each representing a separate electric utility. Utilities routinely buy and sell power to each other as economics and unforeseen circumstances dictate. The transfer of power from one utility to all other utilities with which it is interconnected is called its net interchange. The utility also keeps track of how much power it is generating and how much power it is selling to customers (load). Knowing these three values, generation, load and net interchange, the utility can make the following calculation: Losses = Generation – Load – Net Interchange. Losses represent anything in the system that consumes real power but can’t be billed for it. Generation stations consume large amounts of real power (called station service), transmission lines and transformers lose power in the form of heat energy (I2R losses), etc. As implied, the calculation of losses involves only real power (MegaWatts), yet the system will not operate without the proper flow of reactive power (MegaVars). Without reactive power to support it, the system would not be able to maintain its designed voltage levels. However, it has been customary since the inception of power systems to ignore reactive power in the direct calculation of load and losses.On the Case Information select Model Explorer->Area and then read and record the values of generation, load, interchange and losses for each area:AREA GENERATION LOAD INTERCHANGE LOSSES123For each area, do the losses equal the difference between generation and the sum of load and interchange? __________What is the sum of all the losses? ___________3. Using the mouse, kill the Area Records window and select Edit Mode.Right click on Bus 302 and then select Bus Information Dialog. Verify that this is indeed the system slack bus by clicking on the system slack bus checkbox to unselect it. Click OK at the bottom of the dialog screen and select Run Mode. An error message should pop up saying that the case is now invalid for lack of a slack bus. Again select Edit Mode (the program may do this for you), right click on Page 3ECE 4501 Power Systems Laboratory Manual


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U of M ECE 4501 - POWER SYSTEM SIMULATION

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