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Bundled conductors reduce
Surface electric stress of conductor
Line reactance
Line capacitance
None of above
Surface electric stress of conductor
Bundled conductors are used in EHV/UHV transmission lines to reduce the effective surface electric stress (voltage gradient) at the conductor surface. By using multiple sub-conductors instead of a single large conductor, the total cross-sectional area increases while the surface area is distributed, which effectively lowers the potential gradient that causes corona discharge.
Bundled conductors are used in EHV/UHV transmission lines to reduce the effective surface electric stress (voltage gradient) at the conductor surface. By using multiple sub-conductors instead of a single large conductor, the total cross-sectional area increases while the surface area is distributed, which effectively lowers the potential gradient that causes corona discharge.
EmaxтАЛ=rln(rDтАЛ)VтАЛ тАФ Electric stress at the surface of a single conductor
reqтАЛ=nnтЛЕrтЛЕd(nтИТ1)тАЛ тАФ Equivalent radius of a bundled conductor with n sub-conductors
The electric stress at the surface of a conductor is given by E=rln(D/r)VтАЛ. By using bundled conductors, the geometric mean radius (GMR) of the phase is increased, which effectively mimics a conductor with a larger radius reqтАЛ. Because the potential gradient is inversely proportional to the radius, increasing the effective radius reduces the surface electric stress, thereby suppressing corona loss and radio interference.
Bundled conductors significantly reduce corona loss and radio interference.
They increase the line capacitance, which can be a disadvantage in long lines due to the Ferranti effect.
Bundling decreases the inductive reactance of the transmission line.
Commonly used in lines operating above 220 kV.
Reduction in Corona loss
Decrease in line inductive reactance
Improved power transfer capability
Reduction in radio interference
Increased wind loading due to larger surface area
Higher initial cost and maintenance complexity
Increased line capacitance leads to higher charging currents
Extra High Voltage (EHV) transmission systems
Ultra High Voltage (UHV) transmission lines
Long distance power transmission corridors
While bundling reduces line reactance (Option B) and increases capacitance (Option C), the primary engineering justification for its deployment is the reduction of corona discharge via the reduction of surface electric stress.
Option B is partially true as a side effect, but A is the primary design purpose.
A is correct тАФ Bundled conductors increase the effective radius of the phase, thereby reducing the voltage gradient at the conductor surface.
Always distinguish between the 'primary purpose' and 'secondary effects' of a design feature; while bundled conductors change both L and C, the stress reduction is the specific solution to corona.