多组分变压器油溶解气体的傅里叶变换红外光声光谱定量检测

油中溶解气体是表征充油型变压器早期故障的重要特征量之一,其组分和含量的高精度检测在变压器运行状态评估和故障预警中拥有重要的研究意义。光声痕量气体检测技术作为一种光学检测手段,具有无损、高检测灵敏度、大动态范围和样品无需前处理等优点,有望实现多种变压器油溶解气体的在线检测。基于傅里叶变换红外光谱仪,结合高精度T型共振光声池,建立傅里叶变换红外光声光谱检测系统,选用CO2和C2H2作为气体样品,开展多种变压油中溶解气体定量检测研究。所设计的T型共振光声池主要由相互垂直的吸收腔和共振腔构成,声探测器位于共振腔顶端远离入射光路,避免了杂散光引起的噪声对光声信号的干扰。光声池的共振频率主要由共振腔决定,共振腔与入射光路垂直,其长度不受水平面的狭窄空间的影响,故可在有限的尺寸下实现低频共振,满足光谱仪样品空间需求。实验选用380μL·L^-1 CO2∶1 000μL·L^-1 C2H2∶N2的混合气体作为待测样品,应用光谱仪中的宽谱光源,选用6 cm^-1空间分辨率,采集并分析该气体样品的红外光声谱。所有气体吸收峰清晰可见,说明该方法可完成多种气体的同时检测。在常温常压条件下, 2 349 cm^-1入射光能量仅为12.6μW时, CO2气体的检测精度为4μL·L^-1,满足国家电网公司企业标准(Q/GDW 536-2010)变压器油中溶解气体在线监测装置技术规范中在线监测装置技术指标对CO2气体最低监测极限值的要求;1 360 cm^-1入射光能量为30μW时, C2H2气体在的检测精度为5μL·L^-1,达到中华人民共和国电力行业标准变压器油中溶解气体分析和判断导则(DL/T 722-2014)中对运行中220 kV及以下的变压器和电抗器设备油中溶解气体含量C2H2含量上限的限定。实验结果表明基于T增强型光声池气体检测系统结合了傅里叶红外光谱的广谱特性和光声气体检测技术的高灵敏度,可实现多种变压器油中溶解气体的高精度定量检测,有望为变压器运行状态监测和故障类型分析评估提供理论依据。

Multiple Dissolved Gas Analysis in Transformer Oil Based on Fourier Transform Infrared Photoacoustic Spectroscopy

Trace dissolved gas in transformer oil is a key feature for monitoring the transformers’ status and for estimation of early failure, therefore there is an urgent need for the development of cost-effective on line gas detection methods. As a non-destructive testing method, photoacoustic spectroscopy(PAS) technology is well-known for the advantages of high sensitivity, large dynamic range, and robustness of implementation, which has the potential for the on-line detection of trace dissolved gas detection. A T-resonator enhanced Fourier transform infrared photoacoustic spectroscopic(FTIR-PAS) system is established for the analysis of multiple trace dissolved gases in this paper. The presented T-resonator mainly consists of absorption and resonance cylinders which are perpendicular to each other. A microphone is placed on top of the resonance cylinder away from the incident light path, thus the spurious signal caused by scattered light is avoided and the noise level of the FTIR-PAS configuration is only limited by the microphone itself. The T-cell resonance frequency is determined by the dimension of the resonance cylinder, which results in a solution for the conflicting requirements of low frequency and the limited space of the FTIR compartment. The photoacoustic spectra of the mixture of 380 μL·L^-1 CO2∶1 000 μL·L^-1 C2H2∶N2 with 6 cm^-1 resolution are collected to verify the wavenumber accuracy and multiple trace gas detection ability of the FTIR-PAS technology. The fact that the four absorption bands of CO2 and C2H2 are obviously distinguishable exhibits the good performance for simultaneous multi-dissolved gases detection of the T-resonator enhanced FTIR-PAS configuration. The results show the detection sensitivity yields 4 μL·L^-1 for CO2(light intensity 12.6 μW at 2 349 cm^-1) and 5 μL·L^-1 for C2H2(30 μW at 1 360 cm^-1) under STP conditions. The minimum detection limits of both gases match the national standards for transformers. By virtue of its broadband nature and high sensitivity, the T-resonator enhanced FTIR-PAS methodology is shown to be suitable for simultaneous multiple trace dissolved gas detection in transformer oil.