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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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In alternator, inter turn fault possible in
Stator
Rotor
Both A and B
None of above
Both A and B
Quick Summary: Inter-turn faults occur when the insulation between adjacent turns of the same coil fails, creating a short circuit. This phenomenon can occur in both the stator windings of the alternator (due to high voltage surges or thermal stress) and the field windings of the rotor (due to centrifugal stress and thermal cycling).
Inter-turn faults occur when the insulation between adjacent turns of the same coil fails, creating a short circuit. This phenomenon can occur in both the stator windings of the alternator (due to high voltage surges or thermal stress) and the field windings of the rotor (due to centrifugal stress and thermal cycling).
If=ZsEs — where If is the fault current, Es is the voltage induced in shorted turns, and Zs is the internal impedance of the shorted loop.
The insulation between turns can degrade due to mechanical vibration, chemical contamination, or thermal overload. Once the insulation breaks down, the shorted turns form a closed loop with low impedance. This results in high circulating currents, which cause localized overheating, further worsening the fault and potentially leading to a catastrophic ground fault if left unprotected.
Inter-turn faults are often difficult to detect because the resulting fault current is significantly lower than the rated current.
Detection usually requires longitudinal differential protection or specialized rotor flux monitoring systems.
Stator winding faults often progress into phase-to-ground faults if not cleared.
Rotor inter-turn faults cause magnetic field asymmetry, leading to excessive mechanical vibration.
Differential protection provides high-speed clearing of major phase faults.
Rotor monitoring systems can detect fault progression before machine failure.
Low-level inter-turn faults do not produce high enough current to trip standard overcurrent relays.
Requires high sensitivity protection schemes which may be susceptible to nuisance tripping.
Large turbo-alternators and hydro-generators.
Synchronous machines with multi-turn coil design.
Stator inter-turn faults are more common in high-voltage generators using multi-turn diamond coils.
Rotor inter-turn faults are primarily detected via air-gap flux density measurement or rotor impedance testing during outages.
C is correct — Inter-turn faults represent an insulation failure between turns of the same winding, which can occur in both the stator (armature) and rotor (field) windings of an alternator.
Always remember: While differential protection is standard for phase-to-phase and phase-to-ground faults, inter-turn faults require specific schemes like split-phase or pilot-wire protection in stator windings.