Transmission of large amounts of power over long distances can be accomplished most economically by using extra high voltage(EHV). An increase in transmission voltage results in a reduction of electrical losses, an increase in transmission efficiency, an improvement of voltage regulation, and a reduction in conductor material requirement. At a high voltage above 300Kv, a round single conductor per phase is used, the corona effect cause significant power loss and interference with the communication circuits. If more than one conductor is used per phase it is called bundling of conductors. It is rather preferable to hollow conductors. Lines of 400Kv and higher voltage invariably use Bundled conductors.
Construction of Bundled conductors
A bundled conductor is a conductor made up of two or more conductors, called the sub conductors, per phase nearby compared with the spacing between phases. The sub-conductors of a bundled conductor are separated from each other by a constant distance varying from 0.2 m to 0.6 m depending upon the designed voltage and surrounding conditions throughout the length of the line with the help of spacers whereas the wires of the composite conductor touch each other. The bundled conductors have filter material or air space inside so that the overall diameter is increased. The use of bundled conductors per phase reduces the voltage gradient in the vicinity of the line and thus reduces the possibilities of corona discharge.
Advantages of Bundled conductors over single conductors
The bundled conductor are used on EHV transmission lines primarily to reduce Corona in transmission lines and radio interference. Some of the advantages of bundled conductors over single conductors are as follows:
- The bundled conductor lines transmit bulk power with reduced losses and increase the transmission line efficiency.
- The bundled conductors lines have a higher capacitance to neutral in comparison with single conductor lines. Therefore they have higher charging current which helps in improving the power factor.
- The self GMD and GMR is increased due to the bundling of conductors and the inductance per phase in comparison with single conductor lines is reduced. As a result, reactance per phase is reduced.
- Since the Surge impedance and surge impedance loading of the line given by
the bundled conductor have lower surge impedance with maximum power transfer capability. Since bundled conductors have higher capacitance and lower inductance in comparison with single conductor lines.
GMR for bundled conductor
where r’ is the geometric mean radius of each sub conductor of a bundle and s is the spacing between sub conductors of a bundle.
GMD for bundled conductor
GMD of a bundled conductor line can be determined by taking the root of the product of distances from each conductor of a bundle to every other conductor of the other bundles.
Uses of Bundled conductor
Bundled conductors are used in EHV transmission lines primarily to reduce corona loss and radio interference.