Field experience with the split-phase current signature analysis (SPCSA): Eccentricity assessment for a stand-alone alternator in time-varying and unbalanced load conditions

This paper describes some tests carried out on board an Italian Navy´s ship for validation of a novel technique for on-line monitoring of shaft misalignments in working synchronous generators. The technique is based on the split-phase current signature analysis principle. Rotor eccentricities impact on the split-phase currents of stator windings with parallel connections, producing asymmetry in both amplitudes and phases. Symmetrical components can be applied to carry out a straightforward diagnosis starting from the measurement of those currents. This paper also describes the practical measurements, in presence of unbalanced and step-changing loads. Loads on board ships are usually unbalanced and may change suddenly. However, it is shown that the load-related unbalance can be separated from the eccentricity-related unbalance in the split-phase currents. The paper shows the basics of the split-phase current signature analysis, the practical installation of current transformers in the test generator, the instrumentation set-up, and the results of measurements with various loads, besides some check simulations carried out by using winding functions.