The insulating material for a cable should have

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Examoogle · Accepted Answer

Option D: all of above

Explanation & Concepts:
An ideal insulating material for a power cable must possess a combination of high dielectric strength to prevent breakdown, high mechanical strength to withstand handling and installation stresses, and low cost to ensure the project remains economically viable.

Working Principle: The insulating layer acts as the dielectric medium in the capacitive structure of a cable. Its dielectric strength ($E_{max} = \frac{V}{d}$) determines the maximum voltage it can withstand without insulation failure. Simultaneously, it must be robust enough to handle thermal expansion and mechanical impact during cable laying.

Key Formulas: $E_{max} = \frac{V}{t}$ — Dielectric stress where $V$ is voltage and $t$ is thickness; $R_{ins} = \frac{\rho}{2\pi L} \ln(\frac{D}{d})$ — Insulation resistance calculation

Key Points: High dielectric strength prevents puncture at operating voltages.; Mechanical strength is required for durability against physical stress.; Low cost is essential for large-scale transmission projects.; Additional factors include low dielectric loss and moisture resistance.

Advantages: High reliability of the power system; Cost-effective installation and maintenance; Enhanced protection against short circuits

Disadvantages: High mechanical strength materials are often harder to flex; Low-cost materials may have lower temperature limits

Applications: Underground Power Transmission; Submarine Cables; Control and Instrumentation Wiring

Additional Info: Common materials include Cross-Linked Polyethylene (XLPE) and Ethylene Propylene Rubber (EPR).. Option D is the best answer because the material must balance performance and economics.

Answer: D is correct — An ideal cable insulator must be electrically robust, mechanically sound, and economically feasible.

Exam Tip: Remember that insulation thickness is often governed by dielectric strength, but the overall cable design is governed by the trade-off between material performance and total project cost.

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Option A: low cost

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Option B: high dielectric strength

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Option C: high mechanical strength

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