Which instrument is used to check insulation resistance in armatures and fields?

Which instrument is used to check insulation resistance in armatures and fields?

• A. Megger
• B. Ammeter
• C. Voltmeter
• D. Ohmmeter

Answer: (A)

Insulation resistance testing is about checking how well the windings are insulated from each other and from the machine frame. A megohmmeter, or megger, is the right tool because it applies a high DC voltage to the winding and measures the tiny leakage current that flows through the insulation. The result is an insulation resistance value in megohms. A high resistance means the insulation is sound; a low value points to moisture, dirt, damaged insulation, or other leakage paths that could cause faults once the machine is energized. Armatures and fields are wound parts that must be isolated from the core and from each other. Verifying their insulation helps prevent short circuits or ground faults when the machine starts and runs. Other instruments don’t serve this purpose. An ammeter reads current and won’t tell you about insulation quality. A voltmeter measures voltage but not the resistance of insulation. An ohmmeter checks low resistance to test continuity, not the high resistance of insulation, and it isn’t suited for detecting leakage paths through insulation.

Insulation resistance testing is about checking how well the windings are insulated from each other and from the machine frame. A megohmmeter, or megger, is the right tool because it applies a high DC voltage to the winding and measures the tiny leakage current that flows through the insulation. The result is an insulation resistance value in megohms. A high resistance means the insulation is sound; a low value points to moisture, dirt, damaged insulation, or other leakage paths that could cause faults once the machine is energized.

Armatures and fields are wound parts that must be isolated from the core and from each other. Verifying their insulation helps prevent short circuits or ground faults when the machine starts and runs.

Other instruments don’t serve this purpose. An ammeter reads current and won’t tell you about insulation quality. A voltmeter measures voltage but not the resistance of insulation. An ohmmeter checks low resistance to test continuity, not the high resistance of insulation, and it isn’t suited for detecting leakage paths through insulation.