I . A 2-wire feeder carries a constant current of 250 A throughout the year. The portion of capital cost which is proportional to area of X-section is Rs 5 per kg of copper conductor. The interest and depreciation total 10% per annum and the cost of energy is 5P per kWh.
Find the most economical area of X-section of the conductor. Given that the density of copper is 8.93gm/cm3 and its specific resistance is 1.73 x 10-8 Ω m.
2. Determine the most economical cross-section for a 3-phase transmission line, 1 km long to supply at a constant voltage of 110 kV for the following daily load cycle :
6 hours 20 MW at pj: 0-8 lagging
12 hours 5 MW at pi: 0-8 lagging
6 hours 6 MW at at 0-8 lagging
The line is used for 365 days yearly.
The cost per km of line including erection is Rs (9000 + 6000 a) where 'a' is the area of X-section of conductor in cm2. The annual rate of interest and depreciation is 10% and the energy costs 6P per kWh.
The resistance per km of each conductor is 0.176/a.