DC Bias Diagnosis of Power Transformer with Soundprint Features

DC bias is a common safety threat of AC power transformers. In order to diagnose DC bias problem of power transformer, an acoustic method based on soundprint features are proposed in this paper. The generation mechanism of DC bias is introduced. The noise signals are tested before and after DC bias of the power transformer. After spectral comparison of the signals, four soundprint features are extracted. The noise of more than 150 power transformers is measured onsite. The distribution characteristics of these soundprint features are statistically analyzed and the corresponding threshold values are determined. Based on the soundprint features and the threshold values, the DC bias state of the transformer can be recognized. With the proposed methodology, the operation state of a 500kV autotransformer is diagnosed. The application result shows that DC bias state of power transformer can be accurately detected. The method can be used as reference for the DC bias detection of power transformer.