Bundled Conductors in EHV Transmission Lines:
It is economical to transmit large chunks of power over long distances by employing EHV lines. However, the line voltages that can be used are severely limited by the phenomenon of corona. Corona, in fact, is the result of ionization of the atmosphere when a certain field intensity (about 3,000 kV/m at NTP) is reached. Corona discharge causes communication interference and associated power loss which can be severe in bad weather conditions. Critical line voltage for formation of corona can be raised considerably by the use of bundled conductors in EHV transmission lines, a group of two or more conductors per phase.
Fig. 2.16 shows the bundled conductor in EHV transmission lines.
This increase in critical corona voltage is dependent on number of conductors in the group, the clearance between them and the distance between the groups forming the separate phases.
Reichman has shown that the spacing of Bundled Conductors affects voltage gradient and the optimum spacing is of the order of 8-10 times the conductor’s diameter, irrespective of the number of conductors in the bundle.
Further, because of increased self GMD line inductance is reduced considerably with the incidental advantage of increased transmission capacity of the line.