真型变压器局部放电超高频信号的传播特性

Propagation Characteristics of Utral High Frequency Signals in an Actual Power Transformer

超高频检测法是变压器局部放电在线监测的主要手段之一。由于变压器内部结构复杂,局部放电产生的电磁波在真型变压器内部的传播规律尚不清楚,制约了超高频局部放电检测技术的良好应用。为此,基于一台真型110 kV三相三绕组油浸式变压器,搭建了局部放电超高频信号传播特性检测平台,研究了变压器中局部放电电磁波的传播特性,得出了对应变压器多个检测点处超高频信号的幅值、累积能量、频率和传播时间的变化特性及规律。结果表明:变压器中超高频信号的幅值随着传播距离的增加而非线性地减小,衰减速率减慢;信号的累积能量与幅值的衰减规律相似,但衰减范围更大;电磁波在传播过程中,频率越高,衰减越严重,绕射能力越弱,导致天线检测到信号的主要能量集中在300~600 MHz频带内;检测位置被绕组和铁芯阻挡时,电磁波以绕射方式到达天线,信号波头衰减严重,造成首波到达时刻读取滞后,会降低超高频检测定位的准确性。论文研究可为变压器局部放电超高频检测天线频带、安装位置的选择以及检测灵敏度的提高提供参考和理论依据。

The ultra-high frequency(UHF)detection is one of the important methods for online monitoring of partial discharges in power transformers.Due to the complex internal structure of power transformers,the propagation characteristics of electromagnetic(EM)waves generated by partial discharges in power transformers are not clear,which limits the application of the UHF method to power transformers.In this paper,based on a 110 k V three-phase three-winding oil-immersed power transformer,an experimental platform of UHF detection was established and the propagation characteristics of UHF signals in the power transformer were investigated.The amplitude,cumulative energy,frequency and propagation time of UHF signals at various measuring positions were analyzed.The results show that the amplitude of UHF signals decreases nonlinearly and the attenuation rate slows down with the increasing propagation distance.The cumulative energy of UHF signals has the similar change rules and wider variation range compared with the amplitude.During the propagation process,the higher the frequency of EM waves is,the more attenuation and the weaker diffraction ability will be,thus the main energy of UHF signals will distributes in the 300~600 MHz.When the detection position is blocked by the windings and iron core,EM waves reach antennas by the diffraction.The first wave of the UHF signals is attenuated seriously,which may affect the location accuracy.The research results in this paper can provide reference and theoretical basis for the selection of UHF antenna frequency band,the installation positions of antennas and the improvement of UHF detection sensitivity.