基金项目:
国家自然科学基金(51607066);
河北省自然科学基金(E2020502010);
中央高校基本科研业务费专项资金(2019MS090);
Project supported by National Natural Science Foundation of China(51607066), Natural Science Foundation of Hebei Province(E2020502010), Fundamental Research Funds for the Central Universities(2019MS090);
摘要
为了提高基于布里渊散射的分布式光纤传感的输电线路温度和应变测量的实时性,为基于分布式光纤传感的电气设备振动测量奠定基础,将斜坡法引入输电线路温度和应变测量中来。介绍了布里渊谱模型,基于谱拟合、单斜坡和双斜坡的布里渊频移计算方法,基于实测裸光纤、光纤复合架空地线和光电复合海底电缆中复合光纤的布里渊谱,系统比较了谱拟合法、单斜坡法和双斜坡法的性能。基于数值产生以及实测的光纤沿线布里渊谱研究了工作点以及信噪比对双斜坡法算得布里渊频移误差的影响规律。结果表明:双斜坡法左右2个最佳工作点为光纤沿线布里渊频移的均值加减半个线宽;随信噪比增加布里渊频移误差成指数规律下降;在高信噪比(≥30 dB)和光纤沿线布里渊频移波动程度不大(明显小于1个线宽)时斜坡法可以有接近谱拟合法的准确性;双斜坡法的准确性高于单斜坡法。较之谱拟合法,单斜坡法和双斜坡法可以显著降低谱测量时间,传感距离较短时有望实现对振动的测量且没有相位敏感光时域反射技术(phase-sensitive optical time domain reflectometer, φ-OTDR)测量结果存在不确定性的问题。
关键词 :布里渊散射;
分布式光纤传感;
输电线路;
温度;
应变;
快速测量;
双斜坡法;
DOI:10.13336/j.1003-6520.hve.20200792
ABSTRACT
To improve real-time performance of temperature and strain measurement for transmission lines by use of Brillouin-scattering-based distributed optical fiber sensor, and to lay the foundation for vibration measurement based on distributed optical fiber sensing, the slope-assisted techniques are used to measure the temperature and strain of transmission lines. The Brillouin spectrum model is introduced. Based on the measured Brillouin spectra along bare optical fibers, optical fiber composite overhead ground wires (OPGW), and optical fiber composite submarine power cables, the performances of the spectrum fitting method, slope-assisted technique, and double slope-assisted technique are systematically compared. Based on the numerically generated and measured Brillouin spectra along optical fibers, the influences of working point and signal-to-noise ratio (SNR) on the BFS error estimated by the double slope-assisted technique is investigated. The results reveal that the optimal left and right working points of the double slope-assisted technique are vB0±ΔvB/2, where vB0 and ΔvB respectively are the mean BFS along the optical fiber and the linewidth. BFS error exponentially decreases with SNR. If SNR is high (≥30 dB) and BFS variation along optical fiber is low (significantly less than ΔvB), the slope-assisted techniques have similar accuracy with the spectrum fitting method. The measurement time of the slope-assisted techniques is much shorter than that of the spectrum fitting method. The accuracy of the double slope-assisted technique is higher than that of the slope-assisted technique. The vibration measurement for a short fiber under test can be conducted by the slope-assisted techniques and it can avoid the problem of measurement uncertainty of the φ-OTDR (phase-sensitive optical time domain reflectometer).
图4
裸光纤高信噪比的布里渊谱及拟合结果(叠加平均次数为218,入射光脉宽为200 ns)
Fig.4
Measured spectrum with high SNR for bare fiber and corresponding fitted curve(average time is 218, incident light pulse width is 200 ns)
图10
双斜坡法布里渊频移误差与γ+和γ-的关系(仿真谱)
Fig.10
Change of error in Brillouin frequency shift estimated by double slope-assisted technique with γ+ and γ-(numerically generated spectra)
图11
双斜坡法布里渊频移误差与γ+和γ-的关系(实测谱)
Fig.11
Change of error in Brillouin frequency shift estimated by double slope-assisted technique with γ+ and γ-(measured spectra)
图12
光纤沿线的布里渊频移(仿真)
Fig.12
Brillouin frequency shift along the optical fiber(simulation)
图13
双斜坡法误差与信噪比的关系(仿真谱)
Fig.13
Change of error in Brillouin frequency shift estimated by double slope-assisted technique with SNR(numerically generated spectra)
图14
双斜坡法误差与信噪比的关系(实测谱)
Fig.14
Change of error in Brillouin frequency shift estimated by double slope-assisted technique with SNR(measured spectra)
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