The fault which are likely to occur in cable is

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The correct answer is Option D: All of above. Underground cables are susceptible to various electrical faults primarily due to insulation degradation, mechanical damage, and environmental factors. Common faults include insulation breakdown, short circuits between conductors or phases, and open circuits where the continuity of the cable is lost.

Step-by-Step Solution & Concepts:
Underground cables are susceptible to various electrical faults primarily due to insulation degradation, mechanical damage, and environmental factors. Common faults include insulation breakdown, short circuits between conductors or phases, and open circuits where the continuity of the cable is lost.

Working Principle: 1. Insulation Breakdown: Occurs due to thermal stress, dielectric aging, or moisture ingress, leading to leakage current. 2. Short Circuit Faults: Caused by insulation failure allowing current to bypass the intended load, resulting in high fault currents. 3. Open Circuit Faults: Result from conductor breakage due to mechanical tension, thermal expansion/contraction, or improper jointing, preventing current flow.

Key Formulas: $R_{ins} = \frac{\rho}{2\pi L} \ln(\frac{R}{r})$ — Insulation resistance formula where breakdown often originates; $I_{fault} = \frac{V}{Z_{th}}$ — Typical expression for short-circuit fault current

Key Points: Underground cables face higher thermal and dielectric stress compared to overhead lines.; The most common cause of cable failure is the deterioration of the dielectric (insulation).; Short circuit faults are often detected by protection relays measuring overcurrent or distance.; Open circuit faults are characterized by infinite impedance in the faulty phase.

Advantages: Underground cables are immune to lightning strikes and storms.; Increased public safety due to lack of exposed high-voltage conductors.

Disadvantages: Higher initial cost compared to overhead lines.; Fault localization is significantly more difficult than in overhead lines.

Applications: High-voltage transmission in densely populated urban areas.; Undersea power distribution and submarine cable networks.

Additional Info: Insulation resistance is inversely proportional to the temperature; thus, excessive load leads to faster breakdown.. Option B is often referred to as 'Phase-to-Phase' or 'Phase-to-Earth' faults.

Answer: D is correct — Underground cables can experience insulation breakdown, short circuits, and open circuits due to electrical, mechanical, or chemical stressors.

Exam Tip: When troubleshooting cable faults, remember the Murray loop and Varley loop tests are specifically used to locate ground and short circuit faults.

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Option A: Breakdown of cable insulation

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Option B: Cross for short circuit fault

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Option C: Open circuit fault

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