Final answer:
To test motor winding insulation resistance, a Megohmmeter or Insulation Resistance Tester, which is a specialized ohmmeter operating on Ohm's law, is used. It ensures motor reliability and safety by identifying deteriorated insulation that might lead to failure.
Step-by-step explanation:
The test instrument used to test motor winding insulation resistance is an ohmmeter. An ohmmeter operates based on Ohm's law which states that resistance is equal to voltage divided by current (R = V/I). For measuring the insulation resistance of motor windings, which can be quite high, a specific type of ohmmeter known as a Megohmmeter or Insulation Resistance Tester is commonly used.
This device is designed to apply a high voltage (typically between 500 V to several kilovolts) across the insulation and measure the current that leaks through it. Considering the significance of the test, it's crucial since the insulation resistance affects the motor's performance and safety.
A low resistance value can indicate deteriorated insulation, which could lead to motor failure or hazardous operating conditions due to the risk of short circuits or electrical shocks. Therefore, regular insulation resistance testing is an essential maintenance practice to ensure motor reliability and longevity.