When bundle conductors are used in place of single conductors, the effective inductance and capacitance will r

Question

When bundle conductors are used in place of single conductors, the effective inductance and capacitance will respectively

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Option B: Decrease and increase

Explanation & Concepts:
Bundle conductors effectively increase the Geometric Mean Radius (GMR) of the transmission line, which directly reduces the inductance per phase. Simultaneously, the increase in the effective radius (Geometric Mean Distance or GMD approach) decreases the capacitance per phase relative to a single conductor, leading to increased line capacitance.

Working Principle: When using bundle conductors, the total current is divided among $n$ sub-conductors. This arrangement increases the equivalent radius $r_{eq} = (r \cdot d^{n-1})^{1/n}$, where $r$ is the individual conductor radius and $d$ is the spacing. Since $L = 2 	imes 10^{-7} \ln(\frac{GMD}{GMR})$, increasing the GMR decreases the inductance. Conversely, $C = \frac{2\pi\epsilon}{\ln(GMD/r_{eq})}$; increasing $r_{eq}$ decreases the denominator, thereby increasing the capacitance.

Key Formulas: $L = 2 	imes 10^{-7} \ln(\frac{GMD}{GMR_{bundle}})$ — Inductance of a bundled line; $C = \frac{2\pi\epsilon}{\ln(GMD/r_{bundle})}$ — Capacitance of a bundled line

Key Points: Bundling increases the current carrying capacity due to reduced skin effect.; Corona loss is significantly reduced as the effective diameter increases, lowering the surface voltage gradient.; Surge Impedance ($Z_s = \sqrt{L/C}$) is lowered with bundle conductors.; Effective radius $r_{eq}$ is always larger than the radius of a single conductor.

Advantages: Reduced corona loss and radio interference; Increased power transmission capability; Lower surge impedance improving stability

Disadvantages: Increased wind and ice loading on towers; Higher cost of installation and maintenance; Complex mechanical design for spacers

Applications: EHV (Extra High Voltage) and UHV (Ultra High Voltage) transmission lines; Long-distance power corridors where stability is critical

Additional Info: Bundle conductors are commonly used in $400kV$ and $765kV$ systems.. Option A is incorrect because inductance decreases. Option C is incorrect because capacitance changes. Option D is incorrect because inductance changes.

Answer: B is correct — Bundle conductors increase the effective GMR which decreases inductance, and they increase the effective radius which increases capacitance.

Exam Tip: Always remember that bundling moves the effective surface of the conductor outward; this physical expansion inversely affects L and C via the logarithmic ratio of distances.

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Option A: Increase and decrease

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Option C: Decrease and remain unaffected

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Option D: Remain unaffected and increase

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