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As we know that for operating any power plant we make an economic calculation to run effectively that power plant for the specific period of time & for that we need have to consider its main liabilities like its initial cost, operational cost, & other factors which helpful us to run the plant effectively within all aspects. The load demand on a power system is governed by the consumers and for a system supplying industrial and domestic consumers, it varies within wide limits. This variation of load can be considered as daily, weekly, monthly or yearly. These curves are for a day and for a year and these show the load demanded by the consumers at any particular time. Such load curves are termed as “Chronological load Curves”. If the ordinates of the chronological load curves are arranged in the descending order of magnitude with the highest ordinates on left, a new type of load curve known as “load duration curve” is obtained. a) Daily load curve and b) Yearly load curve Load Curves: The curve showing the variation of load on the power station with respect to with respect to time is known as a load curve. The load on a power station is never constant; it varies from time to time. These load variations during the whole day (i.e., 24 hours) are recorded half-hourly or hourly and are plotted against time on the graph. The curve thus obtained is known as daily load curve as it shows the variations of load w.r.t. the time during the day. The figure below shows a typical daily load curve of a power station. It is clear that load on the power station is varying, being maximum at 6 P.M. in this case. It may be seen that load curve indicates at a glance the general character of the load that is being imposed on the plant. Such a clear representation cannot be obtained from tabulated figures. The monthly load curve can be obtained from the daily load curves of that month. For this purpose, average values of power over a month at different times of the day are calculated and then plotted on the graph. The monthly load curve is generally used to fix the rates of energy. The yearly load curve is obtained by considering the monthly load curves of that particular year. The yearly load curve is generally used to determine the annual load factor.
Load duration curve: When the load elements of a load curve are arranged in the order of descending magnitudes, the curve thus obtained is called a load duration curve.The load duration curve is obtained from the same data as the load curve but the ordinates are arranged in the order of descending magnitudes. In other words, the maximum load is represented to the left and decreasing loads are represented to the right in the descending order. Hence the area under the load duration curve and the area under the load curve are equal. The figure below shows the daily load curve. The daily load duration curve can be readily obtained from it. It is clear from daily load curve, those load elements in order of descending magnitude are 20 MW for 8 hours; 15 MW for 4 hours and 5 MW for 12 hours. Plotting these loads in order of descending magnitude, we get the daily load duration curve as shown in Figure below.
The total cost of electrical energy generated can be divided into three parts, namely ; (i) Fixed cost (ii) Semi-fixed cost (iii) Running or operating cost
B = a constant which when multiplied by the annual kWh generated gives the annual running cost. It is interesting to see here that two-part form is a simplification of three-part form. A little reflection shows that constant “a” of the three part form has been merged in fixed sum per kW maximum demand (i.e. constant A ) in the two-part form. Requirements of tariff - Tariff should satisfy the following requirements: (1) It should be easier to understand. (2) It should provide low rates for high consumption. (3) It should encourage the consumers having high load factors. (4) It should take into account maximum demand charges and energy charges. (5) It should provide fewer charges for power connections than for lighting. (6) It should avoid the complication of separate wiring and metering connections. CASE 1: The following data relate to a 10000 KW thermal station: a. Cost of the plant = Rs 2400 /KW b. Interest, insurance and taxes = 5% pa c. Depreciation = 5% pa d. Cost of primary distribution system = Rs 800000 e. Interest, insurance and taxes & depreciation =5% pa f. Cost of coal including transportation = Rs 200/tonne g. Operating cost = Rs 800000 h. Plant maintenance cost: i. Fixed cost = Rs 40000 pa ii. Variable cost = Rs 60000 pa i. Maximum demand =9000 KW j. Annual load factor =60% k. Consumption of coal =25300 tonne Determine the cost of power generation /KW/year,the cost /KWh generated and the total cost of the generation /KWh. Transmission or primary distribution is chargeable to generation.
1.Explain Load curve and load duration curve? 2.List various types of costs involved in power plant and explain each in detail. 3.Explain the term tariff?