What is the purpose of '100% Stator Earth Fault Protection' in an alternator?

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RRB JE EE 22 Apr 2025 Shift 1 CBT 2 Official Paper

To monitor the voltage regulation of the alternator
To detect and protect against earth faults occurring anywhere in the stator winding
To detect and protect against phase-to-phase faults in the stator winding
To protect the rotor winding from overheating

Answer 1

Stator Earth Fault Protection

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Stator earth fault protection in alternators involves preventing damage to the stator windings when an insulation failure causes a ground fault. This is typically achieved by limiting the ground fault current and detecting and tripping the circuit during a fault.
Stator windings can fail due to insulation breakdown, leading to a short circuit between a winding and the machine's frame (ground).
Stator earth fault protection in generators limits ground fault current to minimize damage to the stator core and windings.
It's achieved by grounding the generator's neutral point with a limited impedance (e.g., a resistor) and using protective relays to detect and respond to earth faults.
Different methods, like 20Hz injection or third harmonic monitoring, are employed to detect and protect various percentages of the stator winding.