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Examoogle • User • info@examoogle.com • EE-2024-8821
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Which fault occurred most?
Overhead line
Underground cable
Switch gear
Transformer
Overhead line
Quick Summary: Overhead lines are the most vulnerable components in a power system because they are exposed to the atmosphere, making them susceptible to transient faults like lightning strikes, falling tree branches, bird contacts, and wind-induced clashing of conductors. Unlike underground cables, switchgear, or transformers which are housed in protected or controlled environments, overhead lines span vast distances through uncontrolled external environments.
Overhead lines are the most vulnerable components in a power system because they are exposed to the atmosphere, making them susceptible to transient faults like lightning strikes, falling tree branches, bird contacts, and wind-induced clashing of conductors. Unlike underground cables, switchgear, or transformers which are housed in protected or controlled environments, overhead lines span vast distances through uncontrolled external environments.
Pfault∝L×Eenv — Probability of fault is proportional to line length L and environmental exposure factor Eenv
Overhead line faults occur due to insulation breakdown between phases or between phase and ground. Common causes include atmospheric overvoltages (lightning), physical contact with foreign objects (trees, animals), or mechanical stress leading to conductor snapping. Because these faults are often transient (arc extinguishes after the power is momentarily interrupted), auto-reclosure mechanisms are highly effective for overhead lines.
Overhead lines account for approximately 80% to 90% of total faults in transmission and distribution networks.
Faults in overhead lines are predominantly transient, whereas cable faults are usually permanent due to insulation puncture.
Transient faults in overhead lines are effectively managed by high-speed auto-reclosing relays.
Transformers and switchgear are considered 'protected' equipment and exhibit lower fault rates compared to lines.
Easier fault localization and repair compared to underground systems.
Cost-effective for long-distance power transmission.
High vulnerability to atmospheric and environmental conditions.
Requires high clearance and right-of-way.
Rural and suburban power distribution.
Long-distance Extra High Voltage (EHV) transmission lines.
Underground cables have low fault frequency but long repair times (MTTR is high).
Transformer faults are rare but typically catastrophic, requiring significant outage time.
Switchgear faults are usually internal (insulation failure) or operational (mechanical failure).
A is correct — Overhead lines are the most frequently faulted component due to their exposed nature and vast geographical extent.
Always remember that while lines have the highest frequency of faults, transformers often represent the highest cost and criticality in power system reliability studies.