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The desired overall diameter of conductor without increasing its cross sectional area can be achieved by
Using aluminum core instead of copper
Stranding the copper conductors around hemp center
Standing the copper conductors over a lead tube
Any of above
Any of above
To increase the overall diameter of a conductor without changing its effective cross-sectional area, materials with lower conductivity or inert cores are utilized to space the conducting strands further apart. This technique is primarily employed to increase the mechanical strength or to adjust the inductance and capacitance of power transmission lines.
To increase the overall diameter of a conductor without changing its effective cross-sectional area, materials with lower conductivity or inert cores are utilized to space the conducting strands further apart. This technique is primarily employed to increase the mechanical strength or to adjust the inductance and capacitance of power transmission lines.
ReffectiveтАЛ=╧АAтАЛтАЛ тАФ Relationship between area and radius
GmaxтАЛ=rln(rDтАЛ)VтАЛ тАФ Electric stress reduction through diameter D increase
The principle relies on displacing the current-carrying strands radially outward. By introducing a central core (like hemp, lead, or low-conductivity metal), the geometric radius R is increased. Since R=2DтАЛ, the overall diameter D increases while the total cross-sectional area of the conducting material remains constant, effectively lowering the surface voltage gradient in EHV lines.
Increasing conductor diameter reduces the corona effect by lowering the surface electric field intensity.
A hemp core is non-conducting and provides structural support while increasing diameter.
Using a lead tube or aluminum core acts as a spacer for the outer copper conducting layers.
This design is crucial for high-voltage transmission lines to minimize power loss due to corona discharge.
Reduction in corona loss
Improved mechanical tensile strength
Enhanced power transmission capacity for a given current
Increased conductor weight
Higher susceptibility to wind-induced vibration (galloping)
Higher cost of manufacturing
Extra High Voltage (EHV) transmission lines
Long-span transmission across rivers or valleys
Underground high-voltage cable manufacturing
Hemp core conductors were traditionally used to achieve a larger diameter in ACSR (Aluminum Conductor Steel Reinforced) style configurations.
The use of hollow conductors or multi-strand arrangements over inert centers is a standard practice in power engineering to mitigate the skin effect and corona.
D is correct тАФ All listed methods provide a physical mechanism to expand the outer dimensions of a conductor while maintaining the specific cross-sectional area of the conductive material.
Remember: Increasing the effective radius of a conductor decreases the surface potential gradient (gmaxтАЛ), which is the primary reason for choosing bundled or hollow conductors in high-voltage engineering.