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 reduction of electrical losses,increase in transmission efficiency,improvement of voltage regulation and reduction in conductor material requirement.At the high voltage above 300Kv ,a round single conductor per phase is used,corona cause a 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 than hollow conductors.Lines of 400Kv and higher voltage invariably use Bundled conductors.
Construction of Bundled conductors
A bundled conductors is a conductor made up of two or more conductors,called the sub conductors,per phase in close proximity 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 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 the corona discharge.
Advantages of Bundled conductor over single conductors
The bundled conductor are used on EHV transmission lines primarily to reduce Corona in transmission line and radio interference.Some of advantage of bundled conductor over single conductors are as follows:
- The bundled conductor lines transmit bulk power with reduced losses and increases 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 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 Surge impedance and surge impedance loading of the line is given by
and the bundled conductor have lower surge impedance with maximum power transfer capability.Since bundled conductor have higher capacitance and lower inductance in comparison with single conductor lines.
Table:Relative power transfer with number of sub-conductors forming a bundle conductor
GMR for bundled conductor
where r’ is the geometric mean radius of each sub conductor of 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 conductor are used in EHV transmission lines primarily to reduce corona loss and radio interference.
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