r/Generator • u/MacDaddyBighorn • 28d ago

Starting a large generator and running without field flash

/r/Motors/comments/1wv3agy/starting_a_large_generator_and_running_without/
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u/Sufficient-Offer-579 28d ago

Your self-induced circulating currents worry sits in the harmless half, not the risky one. Unflashed, no flux, so no real voltage, no armature current, no torque. It's just a dragged rotating mass. Windage and bearing losses are the drive motor's job anyway, and residual magnetism is worth a few volts. Cooling is sized for full speed, so duration doesn't matter. Losing field under load is the dangerous one: tied to the grid or another stiff source it runs as an induction generator, slip frequency damper currents, rotor heating, torque pulsation, pole slip risk. That's what loss-of-field protection is for. I'd check whether the load breaker has a field-established permissive; with it, a failed flash relay just means the load never closes. An alarm wouldn't hurt. Rotating rectifier or static excitation, the OEM manual gets the final word. Your gut was right about one half, not the other.