The condition of the rotor pole insulation is difficult to assess during minor or major generator maintenance outages. Access to the poles is severely restricted without some disassembly and removal of components. Off-line tests like the pole-drop test for detection of shorted turns can also be frustratingly ineffective due to the frequently intermittent nature of the faults at speed and at standstill. These off-line tests are also time-consuming, tying up resources and personnel that during an outage could be better utilized elsewhere. Consequently, on-line measurements are preferred to off-line tests and inspections. Through research funded by EPRI and the New York Power Authority, novel new algorithms for analyzing flux signatures on salient polemotors and generators have been developed to detect rotor pole shorted turns, and incorporated into the Iris Power RFAII-S instrument.​

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• mechanical wear, e.g. caused by frequent start/stop cycling;
• distortion, breakage and cracking due to centrifugal mechanical loading and thermally inducedexpansion/contraction cycles;
• overheating due to overloading, over excitation or inadequate/diminished cooling;

• local overheating at high resistance joints and at the shorted areas of the winding;
• contamination from brake dust or other environmental factors that result in surface tracking between pole turns, or to ground;
• over-voltage induced from system events or from firing circuits in static exciters.
An insulation failure can translate into electrical connections (shorts)between turns in a pole, and eventually a fault to ground.