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Examoogle • User • info@examoogle.com • EE-2024-8821
Chapter 1 of 12 • Page 1 of 248🔒 Protected PDF • Watermarked
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Which fault is related to power transformer?
Overheating of core
Earth fault
Phase to Phase fault
All of above
All of above
Quick Summary: Power transformers are subject to both internal and external electrical and thermal faults. Since core overheating, phase-to-earth, and phase-to-phase faults are all recognized failure modes, the correct answer is 'All of above'.
Power transformers are subject to both internal and external electrical and thermal faults. Since core overheating, phase-to-earth, and phase-to-phase faults are all recognized failure modes, the correct answer is 'All of above'.
Peddy=K⋅Bm2⋅f2⋅t2 — eddy current loss contributing to core overheating
Ifault=ZeqVph — fault current magnitude during phase-to-earth or phase-to-phase faults
Internal faults like insulation breakdown lead to phase-to-phase or phase-to-earth shorts, causing high fault currents. Core overheating is typically caused by breakdown of lamination insulation, leading to eddy current loops that generate excessive heat.
Overheating is often detected via Buchholz relays or temperature sensors.
Phase-to-phase faults are high-current faults causing immediate protection relay operation.
Earth faults are the most common type of fault in transformer windings.
Differential protection covers both phase and earth faults.
Restricted Earth Fault (REF) protection provides sensitive detection for earth faults.
High magnitude faults require fast circuit breaker operation to prevent structural damage.
Cumulative degradation from overheating is difficult to monitor without DGA (Dissolved Gas Analysis).
Power grid distribution transformers
Substation step-up/step-down units
Overheating in the core is primarily due to the breakdown of insulation between laminations, causing high circulating eddy currents.
Phase-to-phase faults involve a short circuit between two windings of the same or different phases.
D is correct — All listed options represent critical fault conditions that can lead to catastrophic transformer failure.
Always remember that Buchholz relay is used for incipient internal faults, while differential protection is used for severe winding faults.