直流偏磁对500 kV变压器振动特性的影响分析

特高压直流工程单极-大地回路运行时，直流电流侵入大型变压器绕组，致使变压器振动加剧。为了深入了解直流偏磁对大型变压器振动特性的影响，分析了变压器的振动机理及直流偏磁的影响机制。在白鹤滩—江苏 ± 800 kV特高压直流输电工程调试期间，对500 kV三相变压器的中性点电流、振动信号进行了实测，量化了直流偏磁程度，分析了不同直流偏磁程度下变压器振动信号时域及频谱特征。提取了波形畸变比、奇偶次谐波能量比、累计能量占比、功率谱熵等特征量来分析直流偏磁对大型变压器振动特性的影响。结果表明：直流偏磁导致波形畸变，1个工频周期内2个半周期对应的振动波形不再对称分布；随着直流偏磁程度增加，振动信号主频分量改变，50 Hz倍频谐波分量增多，其中50 Hz奇次谐波增幅要大于偶次谐波，且影响主要集中在600 Hz以内；由于铁心饱和作用，直流偏磁增大到一定程度时，磁不平衡性降低，振动信号复杂度不再增加。

Influence analysis of DC bias on vibration characteristics of 500 kV transformer

Under the monopole-ground operation mode of ultra-high voltage direct current(UHVDC) transmission project, the direct current(DC) intrudes into the winding of large power transformer, causing vibration of transformer to intensify. In order to deeply understand the influence of DC bias on the vibration characteristics of large power transformer, the vibration mechanism of transformers and the influence of DC bias are analyzed. During the system commissioning of Baihetan-Jiangsu ±800 kV UHVDC power transmission project, the neutral current and vibration signals of 500 kV three-phase transformer are measured, the DC bias degree is quantified, and the time-domain and frequency spectrum characteristics of vibration signal under different DC bias degrees are analyzed. The waveform distortion ratio, odd-even harmonic energy ratio, cumulative energy ratio and power spectrum entropy are extracted to analyze the influence of DC bias on the vibration characteristics of large power transformer. The results show that DC bias leads to waveform distortion and the vibration waveforms of two half-period waveforms within a power frequency period are no longer distributed symmetrically. With the increase of DC bias degree, the main frequency components of vibration signal change, and the 50 Hz doubling components gradually increase, among which the odd harmonic components increase more than the even harmonic components, and the influence is mainly concentrated within 600 Hz. Due to the saturation effect of the iron core, when the DC bias increases to a certain extent, the magnetic unbalance decreases and the complexity of vibration signals no longer increases.