The correct answer is D. All of the above.
Insulation resistance test is a non-destructive test used to measure the insulation resistance of a motor. It is used to determine the condition of the insulation and to identify any potential problems.
The test is conducted by applying a high voltage (usually 500 volts) between the windings and the frame of the motor. The resistance is then measured using an ohmmeter.
A high insulation resistance indicates that the insulation is in good condition. A low insulation resistance indicates that the insulation is damaged and may need to be replaced.
The insulation resistance test can be used to measure the following resistances:
- Phase to phase winding resistance: This is the resistance between the two windings of a three-phase motor.
- Stator winding to earthed frame: This is the resistance between the stator winding and the frame of the motor.
- Rotor winding to earthed shaft: This is the resistance between the rotor winding and the shaft of the motor.
The insulation resistance test is an important part of motor maintenance. It can help to prevent motor failures and to ensure the safety of personnel.