Line designs have been prepared covering temperate and tropical conditions for an alternating voltage of 132-1500kV and a direct voltage of ± 125 to ± 1000kV. The conductors and bundle arrangements were selected taking into consideration corona, radio interference and the factors which influence the current-carrying capacity of a conductor. Evaluation of capital costs of lines and specific transmission costs have been carried out for the above designs. The interrelationship between the conductor size, the load transmitted, the conductor temperature and the specific transmission cost is shown for selected loads. For the typical parameters assumed in the study, it is concluded that, for a given load, the optimum economic transmission cost occurs with a relatively large area of conductor cross-section and at relatively low conductor temperature.
List of symbolsA i = coefficient of convection loss i?, = coefficient of radiation loss C\ = coefficient of heat input from solar radiation C = cost of replacement capacity, £/kVA E = line voltage, kV E' = emissivity of conductor H c = convection loss of a conductor as function of wind speed, temperature rise, conductor diameter etc., W/cm 2 / = current per conductor or snbconductor, A K = coefficient of conductivity K L = capital cost of transmission lines, £/mile L = I 2 R loss per line, MVA LF = annual load factor of the transmission line A^i = number of circuits in a line N 2 = number of subconductors per phase or pole p = power transmitted per line, MVA R = resistance per conductor or subconductor, Q/mile V -wind velocity, cm/s V p = specific transmission cost, £MVA~1mile~1 Y L = annual maintenance charges as a proportion of capital cost of transmission line, %/100 d = conductor diameter, cm k = coefficient of creep for a particular type of conductor k\ = cost of energy losses, £/kWh n = indice in the creep equation p = rate of interest, %/100 r 0 = resistance per conductor or subconductor at 0° C, Cl/cm s = intensity of solar radiation, W/cm 2 / = time in creep equation, h t a = prevailing ambient temperature, degC y = life of transmission lines, year a = temperature resistance coefficient, Q/degC a s = solar absorption coefficient e = creep of conductors, microstrain 0 = temperature rise above ambient, degC A = loss load factor a = Stefan's constant (5-7 x 10~I 2 W/cm 2 K-4 ) ACTM, DCTP, ACTMS, ACTMW etc. nomenclature for the type of system and ambient conditions of line designs. For example, DCTP denotes d.c. line designed for tropical climate; ACTMS or ACTMW denotes an a.c. line designed for temperate climate and specific transmission cost evaluated on the basis of Summer or Winter peak-load operation Paper 6413 P, first received 30th September and in revised form 29th December 1970 Mr. Dey is with the
