The thickness of the layer of insulation on the conductor in cables, depends upon

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Option C: voltage

Explanation & Concepts:
The thickness of insulation on a cable is primarily determined by the operating voltage level. Higher voltage levels generate greater electrical stress, which requires thicker dielectric insulation to prevent insulation failure and dielectric breakdown.

Working Principle: The electrical stress ($g$) at any point in the insulation depends on the potential difference applied between the conductor and the sheath. According to the stress formula $g = \frac{V}{r \ln(R/r)}$, where $V$ is the voltage, $r$ is the conductor radius, and $R$ is the outer radius, the thickness $(R-r)$ must be increased as $V$ increases to ensure the stress remains within the dielectric strength limit of the material.

Key Formulas: $g_{max} = \frac{V}{r \ln(R/r)}$ — maximum stress at the conductor surface; $g_{min} = \frac{V}{R \ln(R/r)}$ — minimum stress at the sheath

Key Points: Insulation thickness protects the system from dielectric breakdown at high voltage potentials.; Higher operating voltages necessitate superior insulating materials and increased radial thickness.; Current carrying capacity determines the cross-sectional area of the conductor, not the thickness of the insulation layer.

Advantages: Prevents arcing between conductor and grounded sheath; Reduces leakage current flow through the insulation

Disadvantages: Increased weight and cost at higher voltage ratings; Larger cable size increases installation complexity

Applications: High voltage power transmission cables; Submarine and underground distribution networks

Additional Info: Current carrying capacity is determined by thermal limits and determines the conductor cross-section, not the insulation thickness.. Power factor is a system characteristic and does not directly dictate the physical thickness of the insulation layer.

Answer: C is correct — The thickness of insulation is chosen based on the voltage rating to prevent insulation breakdown under electrical stress.

Exam Tip: Always remember: Conductor size is determined by current (thermal heating/voltage drop), while insulation thickness is determined by voltage (dielectric stress).

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Option A: reactive power

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Option B: power factor

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Option D: current carrying capacity

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