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The megger is a portable instrument used to measure insulation resistance. The megger consists of a DC generator and a direct reading ohm meter.
The megger measures the insulation resistance between the body of a machine and the armature winding. By applying the operating voltage between the body of machine and the armature winding one can check the insulation resistance. If the reading of the megger is less than 1 Mohm it indicates that there is some fault.
The megger checks the the possible following faults:
1. Burning of armature winding.
2. Sorting between the body of machine and one of the phases.
3. It also checks the dielectric strength of insulation.