Online Diagnosis of Non-Roundness Fault in Rotor Magnetic Pole of a Hydro-Generator

Hydro-generators are characterized by a large diameter, with the rotor magnetic poles installed independently. However, rotor magnetic pole non-roundness (RMPNR) may emerge due to assembly errors or operation factors, leading to tension imbalances, causing unit instability and low-frequency vibrations in both the stator and rotor. The present study examines the fundamental characteristics of RMPNR, starting from air gap magnetic induction and magnetic flux density. By utilizing piercing screws fastened to the stator core as detection coils, the mathematical expression of the induced electromotive force of these coils is derived. It is expected that under the condition of RMPNR, fractional harmonics will emerge in the induced electromotive force of the detection coils, with coils of different pitches exhibiting varying abilities in detecting these harmonics. Ultimately, the efficacy of the detection coils in identifying RMPNR in hydro-generators is demonstrated through finite element simulations and simulated fault experiments. This research introduces a novel technical approach for the online monitoring of RMPNR in hydro-generators, enabling efficient utilization of unit structural components and offering reliable data support for the selection of detection coil pitches.