A 2-core, 11 kV cable is to supply 1 MW at 0.8 pf lag for 3,000 hours in a year. Capital cost of the cable is Rs (20 + 400 a) per metre where a is the x-sectional area of core in cm. Interest and depreciation total 10% and cost per unit of energy is 15 paise. If the length of the cable is 1 km, calculate the most economical x-section of the conductor. The specific resistance of copper is 1.75 x 10-2-cm. Find the most economical x-section of a 3-core feeder cable 250 m long supplying a load of 80 kW. 0.8 pf (lagging) at 400 V for 4,000 hrs per year. The cost of the cable including installation is Rs (150 a 250) per metre where a is the x-section of each conductor in em. Interest and depreciation total 10%. Cost of energy wasted is Rs 1 per unit. The resistance per km of conductor 1 cm cross-section is 0.173 2.