What is the test duration for insulation-resistance tests on AC induction machines larger than 200 horsepower (150 kilowatts) during electrical tests?

The standard test duration for insulation-resistance tests on AC induction machines larger than 200 horsepower (150 kilowatts) is indeed 10 minutes. This duration is established to ensure that the insulation system is adequately evaluated under steady-state conditions, allowing time for any moisture or other contaminants within the insulation to dissipate, and giving a more accurate reflection of the insulation's effectiveness.

During this 10-minute testing interval, the insulation resistance is measured using a megohmmeter, which applies a specific voltage (often 500V or 1000V depending on the application) to assess the integrity of the insulation. The results obtained during this duration help identify any potential insulation failures or degradation that could lead to electrical faults or safety hazards.

Other durations mentioned may not provide sufficient time for reliable readings or are typically reserved for different equipment sizes or specific testing standards. Consequently, 10 minutes is established as a sufficient duration for assessing larger AC induction machines in a thorough and standardized manner.