If insulation resistance trends downward over time in a generator, what is the recommended action?

• A. Ignore the trend and continue operation until a fault occurs.
• B. Increase operating temperature to dry out moisture.
• C. Investigate and repair or re-insulate winding and improve environmental protection and humidity control.
• D. Replace the generator windings with new ones.

Answer: (C)

A falling insulation resistance over time means the winding’s insulation is losing its ability to resist leakage, which typically points to moisture ingress, contamination, aging, or damage. The proper response is to investigate the winding for moisture or contamination, repair or re-insulate the winding as needed, and improve environmental protection and humidity control to stop further degradation. This approach addresses the root cause (deteriorating insulation) and reduces the risk of a progressive fault or a catastrophic failure. After repairs, recheck the insulation resistance and continue monitoring to ensure the trend stabilizes.

Ignoring the trend allows a developing fault to worsen and can lead to an unexpected failure. Merely increasing the operating temperature to dry out moisture may provide a temporary effect but doesn’t fix moisture sources or damaged insulation and can hasten aging. Replacing the windings is a last resort if the insulation is beyond repair; more often, repairing or re-insulating and improving the environment is sufficient.