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Air-Gap Flux Probe Technology for Detecting Rotor Winding Shorted Turns

Air-gap Flux Probe Data

The Generatortech shorted turn detection/analysis system measures flux-density changes in the stator air gap. The flux density reversals at each rotor slot are recorded at multiple loading conditions for later analysis. The flux density at each slot, being a function of the number of active turns, is compared with its opposing pole slot to determine the number of inactive or "shorted" turns.

Figure 1 shows the cross section of a 2-pole rotor and defines the stationary flux probe location. Figure 2 is a digitized waveform from a flux probe recorded during no-load conditions. The nomenclature of the rotor and the associated waveform are identified.

2-pole diagram












Figure 1: Field Nomenclature & Stationary Search Coil - 6 coils per pole


Analysis graph with field nomenclature

Figure 2. Sample analysis graph with no-load data and field nomenclature

Note that the voltage spikes are directly associated with the field slots. The flux probe (sensitive to radial flux variations) provides voltage reversals at the centerline of the slots (labeled) and the centerline of the teeth.

These voltage spike magnitudes are a function of the active turns in the slots (slot leakage flux) plus a distortion factor due to the air-gap flux density waveform.

The success of the detection system requires separating the slot leakage flux data from the distortion factors.

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