Q1. A 300km three phase double circuit 330kV transmission line is constructed on steel lattice towers. The conductor is a quad bundle of "Silicon". The bundle spacing is 450mm. The conductor is initially tensioned to 18% of NBL (Nominal Braking Load) at 15C. The span is 250m. The insulation level is U-362kVms. specified switching impulse withstand voltage. SS1WV-850kVmis (Longitudinal and phase to earth); specified lightning impulse withstand voltage. SLIWV=1050kVo The conductor bundle centre co-ordinates (x,y) = (distance from centre line of the towers height above ground) are Circuit 1: Phase R (5m. 20m); Phase S (6m. 27m); Phase T (5m 34m) Circuit 2: Phase S - (-5m. 20m); Phase T- (-6m. 27m); Phase R- (-5m, 34m) Earth Wire 1 (-3.5m 43m); Earth Wire 2 (3.5m, 43m) (a) Draw the placement of the conductors and determine the shielding angle provided to the phases by the earth wires (b) What is the conductor sag for the initial stringing condition? (c) The line is loaded to 500MW at unity power factor. What are the resistive losses on a per kilometre basis? (d) Is the selected conductor size above or below the optimum economic conductor size? Assume S80/MWhr for losses, a suspended conductor cost of S25/kg and net present value multiplier of 11.5 (20years with 6% real rate of interest) (e) Estimate the Surge Impedance Loading of this line (f) Disk insulators 280x170mm, with a normal profile are available. They have a nominal creepage distance of 405mm. Determine the number of units required in the insulator string to meet each requirements for the specified insulation level in a medium pollution environment (20mm/kV) (g) Determine the corona disruptive critical voltage for this line in fair weather Hint: Neglect the mutual inductance/capacitance between the 2 circuits Number of 280x170mn Disks 10 11 12 13 14 15 1617 18 19 Power Frequency Withstand Dry580 625 675 720 760 800840 880 920955 Wet 375 410 450 485525560 600 635 675 710 Voltage Impulse Positive Withstand and 940 102511551200 1285 1370 14601545 1630 1720 VoltageNegative Silicon - AAAC 61/3.50; nominal diameter 31.5mm; Cross section 587mm Approximate mass 1620kg/km breaking load 127kN; Modulus of Elasticity 64GPa; Coefficient of Thermal Expansion 23x10/C; AC Resistance 75C 0.0634 Summer noon still air industrial weathered rating 488A