Detecting Turn Shorts in Rotor Windings: A New Test Using Magnetic Flux Monitoring

Gradual aging of the turn insulation in salient pole rotor windings can eventually lead to shorted turns. These shorted turns may create the high vibration of the rotor, and, in severe cases where there are few poles and a number of shorted turns, the probability of a motor shutdown due to high vibration increases. The most widely applied method for detecting shorted turns in the rotor is the pole-drop test. Since this test is done with the rotor not spinning, the test may not find all the shorts that can occur in service. Also, the pole-drop test is usually performed infrequently, and thus the need for rotor refurbishment is often a surprise, which can extend the turnaround duration. Research has led to a new online test that can detect the shorted turns during normal service, by measuring the magnetic flux from each rotor pole using a stator-based magnetic flux sensor. Initial results with the new technology were presented.