Transformer Winding Vibration Enveloping for Empirical Mode Decomposition Based on Non-uniform B-Spline Fitting

A new method of envelope fitting for empirical mode decomposing data based on non-uniform B-spline curve is developed. Empirical mode decomposition obtained local characteristic of data, which provided high-resolution time-frequency characteristics for non-stationary signal. This new method of envelope fitting was provided for overshoots and undershoots of polynomial spline. B-spline interpolation curves were obtained to use the knots of B-spline, control vertexes and control polygon determined by the extrema. Envelope fitting based on non-uniform B-spline curve handles the incomplete envelope effects of empirical mode decomposition. The decomposing results of transformer winding vibration show that intrinsic mode functions derived by B-spline fitting alleviate large swings. Left by themselves, the end swings can eventually propagate inward and corrupt the whole data span. It is demonstrated by actual analysis that the new envelope fitting method is one effective way for signal processing.