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Page 1 ECONOMIC DISPATCH AND UNIT COMMITMENT ECONOMIC DISPATCH AND UNIT COMMITMENT Page 2 ECONOMIC DISPATCH AND UNIT COMMITMENT ECONOMIC DISPATCH AND UNIT COMMITMENT 1 INTRODUCTION A power system has several power plants. Each power plant has several generating units. At any point of time, the total load in the system is met by the generating units in different power plants. Economic dispatch control determines the power output of each power plant, and power output of each generating unit within a power plant , which will minimize the overall cost of fuel needed to serve the system load. • We study first the most economical distribution of the output of a • We study first the most economical distribution of the output of a power plant between the generating units in that plant. The method we develop also applies to economic scheduling of plant outputs for a given system load without considering the transmission loss. • Next, we express the transmission loss as a function of output of the various plants. • Then, we determine how the output of each of the plants of a system is scheduled to achieve the total cost of generation minimum, simultaneously meeting the load on the system. Page 3 ECONOMIC DISPATCH AND UNIT COMMITMENT ECONOMIC DISPATCH AND UNIT COMMITMENT 1 INTRODUCTION A power system has several power plants. Each power plant has several generating units. At any point of time, the total load in the system is met by the generating units in different power plants. Economic dispatch control determines the power output of each power plant, and power output of each generating unit within a power plant , which will minimize the overall cost of fuel needed to serve the system load. • We study first the most economical distribution of the output of a • We study first the most economical distribution of the output of a power plant between the generating units in that plant. The method we develop also applies to economic scheduling of plant outputs for a given system load without considering the transmission loss. • Next, we express the transmission loss as a function of output of the various plants. • Then, we determine how the output of each of the plants of a system is scheduled to achieve the total cost of generation minimum, simultaneously meeting the load on the system. 2 INPUT – OUTPUT CURVE OF GENERATING UNIT Power plants consisting of several generating units are constructed investing huge amount of money. Fuel cost, staff salary, interest and depreciation charges and maintenance cost are some of the components of operating cost. Fuel cost is the major portion of operating cost and it of operating cost. Fuel cost is the major portion of operating cost and it can be controlled. Therefore, we shall consider the fuel cost alone for further consideration. Page 4 ECONOMIC DISPATCH AND UNIT COMMITMENT ECONOMIC DISPATCH AND UNIT COMMITMENT 1 INTRODUCTION A power system has several power plants. Each power plant has several generating units. At any point of time, the total load in the system is met by the generating units in different power plants. Economic dispatch control determines the power output of each power plant, and power output of each generating unit within a power plant , which will minimize the overall cost of fuel needed to serve the system load. • We study first the most economical distribution of the output of a • We study first the most economical distribution of the output of a power plant between the generating units in that plant. The method we develop also applies to economic scheduling of plant outputs for a given system load without considering the transmission loss. • Next, we express the transmission loss as a function of output of the various plants. • Then, we determine how the output of each of the plants of a system is scheduled to achieve the total cost of generation minimum, simultaneously meeting the load on the system. 2 INPUT – OUTPUT CURVE OF GENERATING UNIT Power plants consisting of several generating units are constructed investing huge amount of money. Fuel cost, staff salary, interest and depreciation charges and maintenance cost are some of the components of operating cost. Fuel cost is the major portion of operating cost and it of operating cost. Fuel cost is the major portion of operating cost and it can be controlled. Therefore, we shall consider the fuel cost alone for further consideration. C i in Rs / h To get different output power, we need to vary the fuel input. Fuel input can be measured in Tonnes / hour or Millions of Btu / hour. Knowing the cost of the fuel, in terms of Rs. / Tonne or Rs. / Millions of Btu, input to the generating unit can be expressed as Rs / hour. Let C i Rs / h be the input cost to generate a power of P i MW in unit i. Fig.1 shows a typical input – output curve of a generating unit. For each generating unit there shall be a minimum and a maximum power generated as P i min and P i max . in Rs / h P i min P i in MW Fig.1 Input-Output curve of a generating unit max i P Page 5 ECONOMIC DISPATCH AND UNIT COMMITMENT ECONOMIC DISPATCH AND UNIT COMMITMENT 1 INTRODUCTION A power system has several power plants. Each power plant has several generating units. At any point of time, the total load in the system is met by the generating units in different power plants. Economic dispatch control determines the power output of each power plant, and power output of each generating unit within a power plant , which will minimize the overall cost of fuel needed to serve the system load. • We study first the most economical distribution of the output of a • We study first the most economical distribution of the output of a power plant between the generating units in that plant. The method we develop also applies to economic scheduling of plant outputs for a given system load without considering the transmission loss. • Next, we express the transmission loss as a function of output of the various plants. • Then, we determine how the output of each of the plants of a system is scheduled to achieve the total cost of generation minimum, simultaneously meeting the load on the system. 2 INPUT – OUTPUT CURVE OF GENERATING UNIT Power plants consisting of several generating units are constructed investing huge amount of money. Fuel cost, staff salary, interest and depreciation charges and maintenance cost are some of the components of operating cost. Fuel cost is the major portion of operating cost and it of operating cost. Fuel cost is the major portion of operating cost and it can be controlled. Therefore, we shall consider the fuel cost alone for further consideration. C i in Rs / h To get different output power, we need to vary the fuel input. Fuel input can be measured in Tonnes / hour or Millions of Btu / hour. Knowing the cost of the fuel, in terms of Rs. / Tonne or Rs. / Millions of Btu, input to the generating unit can be expressed as Rs / hour. Let C i Rs / h be the input cost to generate a power of P i MW in unit i. Fig.1 shows a typical input – output curve of a generating unit. For each generating unit there shall be a minimum and a maximum power generated as P i min and P i max . in Rs / h P i min P i in MW Fig.1 Input-Output curve of a generating unit max i P If the input-output curve of unit i is quadratic, we can write i i i 2 i i i ? P ß P a C + + = Rs / h (1) A power plant may have several generator units. If the input-output characteristic of different generator units are identical, then the generating units can be equally loaded. But generating units will generally have different input-output characteristic. This means that, for particular input cost, the generator power P i will be different for different generating units in a plant. 3 INCREMENTAL COST CURVE As we shall see, the criterion for distribution of the load between any two units is based on whether increasing the generation of one unit, and decreasing the generation of the other unit by the same amount results in an increase or decrease in total cost. This can be obtained if we can calculate the change in input cost ?C i for a small change in power ?P i . Since i i dP dC = i i ?P ?C we can write ?C i = i i dP dC ?P iRead More
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