Improvement of the efficiency of 35 to 220 kV lines

It is good practice to limit the ratio of transmitted power to surge impedance loading (SIL, or natural capacity), S/P_n, to ⩽1, with the aim of reducing voltage drop and power losses. The use of flat phases and reduced phase spacings enable the ratio S/P_n to be confined to ⩽1, which considerably enhances the economic efficiency and quality of power transmission, enables the transmission distance to be increased and the operational lifetime of existing systems to be extended. Conductor bundling and ultimate reduction of phase spacings, down to distances determined by the requirements of reliable operation and lightning surges, allow an increase in the transmission capacity of 35 to 220 kV lines virtually in proportion to the number of subconductors per phase, i.e., by a factor of 3, 4 or more as compared to traditional lines. An increased transmission capacity of compact lines is attained with relatively small phase sizes