power System iv lectures.pdf - 1 Power Systems IV Dr Upuli...

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Power Systems IV Dr. Upuli Jayatunga Department of Electrical Eng 1
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Different generating options to meet the current load Power system loads are dynamic. The installed generation capacity is usually much greater than the current load. Generated electrical power can not be stored Planning of power system economic operation: Which power plants to be operated?, when to start/shut down?, for how long to be operated? Unit Commitment How much Power output of each generating unit or optimum loading of generators? Economic dispatch 2 Power System Economic Operation
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Determination of optimal scheduling of power plant operation Normally one day to one week planning time horizon Optimization problem where the total operating cost to be minimized Constraints: fuel costs, network losses costs of start up, running and shut down of plants Spinning Reserve : Total amount of generation available from all synchronized generating units in the system (Present load+ network losses) Unit commitment
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How to dispatch committed generators to supply a given demand in a way that total operating cost is minimized Different Approaches: 1. Merit Order 2. Incremental cost 3. Coordination equations 4. Optimal power flow analysis First 3 methods deal only with active power dispatch Economic Dispatch
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Determine the generation dispatch that minimizes the instantaneous operating cost, subject to the constraint that total generation = total load + losses Economic Dispatch T 1 m i=1 Minimize C ( ) Such that m i Gi i Gi D Losses C P P P P
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Generation costs can vary widely with different technologies balancing capital costs necessary to build the generator costs to actually produce electric power Thermal Vs Hydro generation For hydro, fuel (water) is free but there may be many constraints on operation fixed amounts of water available reservoir levels must be managed and coordinated downstream flow rates for irrigation, fish and navigation Hydro optimization is typically longer term (many months or years) Economic Dispatch
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Traditionally utilities have three broad groups of generators Base-load units: large coal/nuclear; always on at max. Mid-load units: smaller coal that cycle on/off daily Peak load units: combustion turbines used only for several hours during periods of high demand 7
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Consider ED as a static problem Power plants are arranged in order to their operating costs Plant with lowest operating cost is loaded first Deficiencies: Ignore transmission constraints assume constant operating cost through out the load range of a plant Merit Order Dispatch
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Generator Input Output Characteristics Generators have limits on the minimum and maximum amount of power they can produce Nonlinear input output characteristics: Generator costs are typically represented by : input/output (I/O) curve fuel-cost curve heat-rate curve incremental cost curve For reference - 1 Btu (British thermal unit) = 1054 J - 1 MBtu = 1x10 6 Btu - 1 MBtu = 0.29 MWh 9
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Input-Output curve for a generating unit - relationship between total fuel input and power output 10
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  • Fall '06
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