​The condition of the rotor pole insulation is difficult to assess during minor or major 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 bebetter utilized elsewhere. Consequently, continuous on-line measurements are preferred tooff-line tests and inspections.

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The Iris Power FluxTracII-S instrument is a continuous on-line rotor flux monitor for rotor winding shorted turn detection in salient pole machines such as hydro generators, motor- generators in reversible pump- turbines, and salient pole motors. It was developed in cooperation​ with the US Electric Power Research Institute, the New York Power Authority, and the US Bureau of Reclamation.

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Flux monitoring relies on measurements of the local magnetic field emanated from each rotor pole. Factors affecting the magnetic field from each pole include:

• Air-gap size change

• Rotor out-of-round or off-centre ​

• Stator migration
• Loose pole – key migration

• Stator migration​

• Natural variations of pole’s physical position
• Shorted turns on a pole