Diagnosis of DC Bias in Power Transformers Using Vibration Feature Extraction and a Pattern Recognition Method

Xiaowen Wu,Nianguang Zhou,Sheng Hu,Ling Lu,Hao Cao,Zhiqiang He,Ling Li

doi:10.3390/en11071775

Xiaowen Wu, Nianguang Zhou + Show 5 more

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https://doi.org/10.3390/en11071775

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Abstract

DC bias is a great threat to the safe operation of power transformers. This paper deals with a new vibration-based technique to diagnose DC bias in power transformers. With this technique, the DC bias status of power transformers can be automatically recognized. The vibration variation process of a 500 kV autotransformer is tested under the influence of DC bias in the monopole trail operation stage of a ±800 kV HVDC transmission system. Comparison of transformer vibration under normal and DC-biased conditions is conducted. Three features are proposed and are validated by sensitivity analysis. The principal component analysis method is employed for feature de-correlation and dimensionality reduction. The least square support vector machine algorithm is used and verified successful in DC bias recognition. A remote on-line monitoring device based on the proposed algorithm is designed and applied in field DC bias diagnosis of power transformers. The suggested diagnostic algorithm and monitoring device could be useful in targeted DC bias control and improving the safe operation level of power transformers.

Highlights

It is widely recognized that failures in power transformers usually lead to long outage times and great repair costs
The calculated 126 sets of principal features are used to train the classifier of LS-support vector machine (SVM) with a toolbox called least square SVM (LS-SVM) lab [34]
Vibration feature selection is a critical issue in the DC bias diagnosis process

Summary

Introduction

It is widely recognized that failures in power transformers usually lead to long outage times and great repair costs. Substantial efforts have been devoted to diagnosing anomalous operation conditions in power transformers after they have been put into service [1,2,3,4,5,6,7]. Many high voltage direct current (HVDC) power transmission projects have been constructed in China. When the HVDC transmission system operates in monopole Earth return mode, direct current will flow through the AC power transformer with grounded neutral, which causes DC bias problem [8]. Since transformer noise and vibration are mainly caused by magnetostriction force in the cores and electromagnetic force in the windings, distorted magnetizing currents will induce numerous high-order harmonic frequency components in the vibration forces

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