变压器局部放电超高频信号的外部检测

电力变压器局部放电超高频检测法中一般将传感器安装于箱体内部,这对已投入运行的变压器来说是有潜在危害的。为此,先分析了变压器箱体对局部放电超高频电磁波传播的影响,探讨了接收天线外部检测超高频信号的可行性,再实验研究了局放超高频电磁波的外传播特性。结果表明,超高频电磁波可以透过变压器箱体夹缝衍射出来,外部检测到的超高频信号强度随着变压器箱体缝宽增大而增大;变压器套管附近安装接收天线也能检测到超高频信号。

UHF Signal External Detection of Partial Discharge in Transformers

Partial discharge(PD) is a symptom of the insulation deterioration in transformers.Detecting PD,therefore,is an important strategy to monitor the condition of the insulation system of transformers.Several techniques are applied to this field including acoustic,electrical and chemical methods.Ultra High Frequency(UHF) technique which is developed in recent years is one of the electrical methods.Through detecting UHF E-M waves emitted from PD sources,PDs could be detected in transformers.UHF detection technique has some advantages that the measuring frequency is high,much interference such as corona can be rejected,the SNR(signal noise rate) is high and the sensitivity and the reliability are both good.Usually,UHF sensors are installed in the transformer tank.However,there will be potential peril for transformers in service.The effect of transformer tank on UHF wave propagation is analyzed in this paper.The feasibility of using external UHF sensor for detecting partial discharge activities is discussed,and then outside propagation characteristic of UHF E-M wave is experimentally studied.The results show that UHF signals could leak outside the transformer through the cracks after multiple refraction and reflection in the transformer tank.An antenna outside the tank could receive the signals.The size of the crack will influence the strength of the received signal,the bigger the crack is,the bigger the strength will be.Meanwhile,the research results show that UHF signal can be received around the bushing.