Air Gap (Rotor) Flux Test

Flux monitoring via permanently mounted air gap flux probes is a proven technology in synchronous machines to determine if turn-to-turn shorts have occurred in the rotor winding. Flux measurements are the most powerful means of monitoring the condition of rotor windings on-line and can provide information on the integrity of the rotor winding inter-turn insulation. This information is critical in planning maintenance, explaining abnormal vibrations, and verifying new and rewound rotor integrity.

To maximize the sensitivity to shorted turns in all rotor slots, the signals from the flux probe needs to be measured under different load conditions ranging from no load to full load. At a zero crossing of the total flux (which is a function of the real and reactive load of the machine), the sensitivity to the leakage flux is highest. Thus, flux readings are taken at various load points depending on the number of slot pairs in a pole pair. With the waveforms digitally recorded at each load step, flux monitor can determine the number of shorted turns in each slot, as well as identify the slots with the shorts.

Flux measurements are done utilizing portable instrumentation to digitize the signals and specialized software or expert interpretation via a permanently connected flux probe.

Application includes: Generator Rotors