In a megger test on a hermetic motor in deep vacuum, which outcome is expected if performed?

In a megger test on a hermetic motor in deep vacuum, which outcome is expected if performed?

• A. The insulation would be damaged by arcing
• B. The insulation would be cooled
• C. The dielectric strength would be greatly reduced
• D. The motor would spin normally

Answer: (C)

The main idea is: a megger test checks how much voltage the insulation can withstand before breaking down. Dielectric strength is that withstand capability. In deep vacuum, there is almost no gas around the insulation, so breakdown pathways shift from gas breakdown to the solid insulation itself and along its surfaces. Any voids, contaminants, or outgassed products inside the insulation can form localized discharge paths under high voltage, making breakdown occur at a lower voltage than it would in normal conditions. That’s why the dielectric strength is greatly reduced in this vacuum environment. The other options don’t describe what the megger voltage test enforces or what vacuum does to insulation behavior.

The main idea is: a megger test checks how much voltage the insulation can withstand before breaking down. Dielectric strength is that withstand capability. In deep vacuum, there is almost no gas around the insulation, so breakdown pathways shift from gas breakdown to the solid insulation itself and along its surfaces. Any voids, contaminants, or outgassed products inside the insulation can form localized discharge paths under high voltage, making breakdown occur at a lower voltage than it would in normal conditions. That’s why the dielectric strength is greatly reduced in this vacuum environment. The other options don’t describe what the megger voltage test enforces or what vacuum does to insulation behavior.