A New External Search Coil Based Method to Detect Detailed Static Air-Gap Eccentricity Position in Nonsalient Pole Synchronous Generators

This research investigates the detection of the detailed static air-gap eccentricity position (SAGE) at both the ends of nonsalient pole synchronous generators (SG). Differently from the previous studies, the detection method proposed does not necessitate the installation of invasive sensors inside the generator and instead, it is based on two groups of symmetrically distributed search coils placed at both endsides outside the generator. The root-mean-square (rms) value comparison in electromotive forces of the search coils is then employed to assess the exact SAGE position of each end-side. Numerical 3-D finite element calculation together with an experimental campaign on a two-pole 3000 r/min CS-5 prototype SG validates the effectiveness of the proposed method. It is shown that the maximum assessment error by using the four external search coils at each end is 15.1%, while by setting more coils, the error can be significantly reduced. Since this proposed method has no need to install invasive search coils inside the generator, it is more convenient for field testing and helps improve the cost performance of the online SAGE condition monitoring.