Corona loss by the hollow conductors because

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Option C: For a given cross section, radius of conductor is increased

Explanation & Concepts:
Corona loss is directly related to the surface electric field intensity of the conductor. By using hollow conductors, the effective radius (r) of the conductor is increased for the same cross-sectional area, which reduces the surface potential gradient and consequently the corona loss.

Working Principle: The visual and electrical discharge known as corona occurs when the voltage gradient at the conductor surface exceeds the breakdown strength of air. According to Peek's law, corona loss is proportional to $(V - V_c)^2$, where $V_c$ is the disruptive critical voltage. $V_c$ is proportional to the radius of the conductor; thus, increasing the radius through hollow construction raises the disruptive voltage threshold, decreasing power loss.

Key Formulas: $V_c = g_0 \cdot \delta \cdot r \cdot \ln\left(\frac{d}{r}\right)$ — Disruptive critical voltage formula where $r$ is the radius.; $P_c \propto (V - V_c)^2$ — Corona power loss proportional to the square of voltage excess.

Key Points: Corona loss is inversely proportional to the logarithm of the ratio of spacing to radius.; Hollow conductors are primarily used in EHV/UHV lines to manage corona discharge.; Increasing the radius reduces the surface voltage gradient ($E = V / (r \ln(d/r))$).

Advantages: Reduces corona loss significantly; Reduces radio interference; Reduces electromagnetic noise

Disadvantages: Higher manufacturing complexity; Mechanical strength is lower compared to solid conductors of equal diameter

Applications: Extra High Voltage (EHV) transmission lines; Ultra High Voltage (UHV) transmission lines

Additional Info: Option A is incorrect because current density reduction is a consequence of increased area, but for fixed cross-section, hollow design specifically targets radius.. Option B is incorrect as hollow conductors do not eliminate eddy currents; they might even influence skin effect distributions.

Answer: C is correct — Increasing the conductor radius for a given cross-sectional area reduces the surface potential gradient, which effectively minimizes corona loss.

Exam Tip: Always remember that corona is a surface phenomenon; any design modification that lowers the surface electric field intensity without increasing the total conductor volume will help mitigate it.

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Option A: Current density is reduced

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Option B: Eddy current in the conductor is eliminated

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Option D: Of better ventilation in the conductor

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