What is the most suitable device for testing conductor insulation at voltages near the operating voltage?

The most suitable device for testing conductor insulation at voltages near the operating voltage is a megohmmeter. This instrument is specifically designed to apply high voltage levels to insulation materials in order to assess their integrity and insulation resistance properties. It typically operates at voltages significantly higher than the standard operating voltage of the equipment being tested, which can provide valuable information about how the insulation will perform under normal operating conditions.

When a megohmmeter is used, it generates a test voltage that helps identify any weaknesses or breakdowns in the insulation that may not be detectable at lower voltage levels. This capability is crucial for ensuring that the insulation can withstand the stresses it will encounter during normal operation.

Other devices listed, such as a low-resistance ohmmeter, insulation ohmmeter, and multimeter, serve different purposes. While low-resistance ohmmeters measure resistance at low voltages, insulation ohmeters are primarily designed for insulation testing, and multimeters are versatile but do not apply elevated test voltages necessary for a thorough insulation assessment. Therefore, the megohmmeter stands out as the most appropriate choice for this specific type of testing.