Comparative Study of Neutral-Voltage-Based and Leakage-Current-Based Online Condition Monitoring Methods for Stator Insulation of Inverter-Fed Machines

In recent years, online condition monitoring methods have gained popularity for their ability to predict latent insulation failure in electrical machines. Most of the existing methods are based on leakage current measurement. While neutral-voltage-based methods were firstly introduced for transformer monitoring, recent research has explored their application to electrical machines. However, the process of selecting the most suitable method for specific condition monitoring requirements remains ambiguous. This aricle offers a comprehensive comparison of the advantages and disadvantages of these methods, grounded in a theoretical analysis of the stator winding model. Sensitivities to various insulation aging problems are also studied, considering signal-to-noise ratios (SNRs) to determine the most suitable features for monitoring different aging issues. Additionally, a novel phase-to-ground insulation aging monitoring method is introduced, which accounts for the aging position along the winding. This method is based on the common-mode impedance spectrum and offers the benefit of reducing sensor bandwidth requirements when compared to existing methods. This research contributes to the refinement of condition monitoring for electrical machines, enabling more precise and efficient early detection of insulation aging problems.