Faraday镜预转角对FMOCT输出光偏振态的影响

通过计算机仿真，运用琼斯矩阵理论分析了Faraday镜预转角对法拉第镜式光学电流互感器输出光偏振态的影响.实验测量了Faraday镜实际预转角的大小，测量了外磁场的改变对Faraday镜预转角的影响.外磁场的存在和变化使Faraday镜预转角偏离初始值，并使系统输出光由理想状态下的线偏振光退化成椭圆偏振光，并引起法拉第镜式光学电流互感器工作灵敏度和稳定性的下降.提出了用电磁屏蔽解决外界磁场影响的方法.     

Measurement of currents and floating potential in multilayer sensor due to oil-flow electrification

This paper presents floating potential and current measurements due to oil-flow electrification inside a multilayer sensor incorporated in a closed loop filled with fresh transformer oil. All leakage currents at the sensor inlet and outlet, the capacitive current and the streaming current are measured. The waveforms of these currents, floating potential as well as the oil temperature at the sensor inlet are simultaneously recorded for laminar flow and at controlled operating conditions. The measured floating potentials are compared with the calculated ones under different oil-flow velocities and good agreement has been found.     

保偏反射膜温度特性对BGOCT灵敏度影响的理论研究

采用琼斯矩阵方法对保偏膜反射相移温度特性对块状光学电流互感器（BGOCT）灵敏度的影响作了理论研究,结果表明,当温度从5.3℃变化到39℃时,表征系统灵敏度的归一化尺度因子会在一定范围内变化.表明镀制于光学玻璃电流传感头上的保偏膜反射相移温度特性影响光学电流传感器的稳定性.因此,在实际系统设计中对光学玻璃电流传感头应采取必要的温度控制或补偿措施.     

变压器典型工作环境对声功率测量结果的影响

变压器两侧常建有高大的防火墙,其从声学角度可视为刚性反射壁面,会改变变压器的辐射声场,进而影响变压器声功率测量结果。本文利用有限元、边界元等数值计算方法建立了变压器声辐射的仿真模型用以分析反射壁面对变压器声功率测量结果的影响,并通过实际测量验证了仿真计算所得结论。结果表明,反射壁面对变压器声功率测量结果的影响程度随反射壁面到变压器箱体距离增加而减弱,且当反射壁面距变压器箱体5 m以上时,其对变压器声功率基频及各谐波成份测量结果的影响均在2 dB以内。另外反射壁面对变压器噪声高频成份声功率测量结果的影响较大,而对100 Hz、200 Hz等低频成份测量结果影响较小,基本低于3 dB。     

Kinetics and mechanisms of the low-temperature degradation of cellulose

A critical review is given of the degradation of cellulose in the low-temperature region (below about 300°C) of power transformer operation. The large number of kinetic studies, under a variety of environmental conditions from Kraft paper in insulating oil, to cotton and paper in oxygen, are considered in terms of a first-order polymer chain scission model. In many cases, the data are replotted to suit the model. A common activation energy of 111±6 kjmol^–1 is calculated and it is shown that the pre-exponential factor, rather than the activation energy, is sensitive to the oxidizing nature of the environment and the susceptibility to degradation of the material. The chemical mechanisms of degradation are reviewed, and conclusions and recommendations are made regarding chemical condition monitoring and life prediction of electrical insulation.     

A solid-state NMR study of cellulose degradation

A series of laboratory-aged transformer insulating papers were investigated using solid-state NMR spectroscopy. Carbon-13 CPMAS, and proton MAS experiments were carried out along with static proton relaxation (T₁, and T₁) and free induction decay (FID) measurements. Some proton CRAMPS and proton-carbon-13 correlation (WISE) experiments were also undertaken. A change in the proton T₁ and FID with ageing was detected. No detectable change was found in the proton T₁. Some amorphous cellulose was detected in the carbon-13 spectrum. There was, however, no evidence for a substantial change in the nature of the cellulose with ageing. The carbon-13 spectra from some aged samples showed signals not present in the spectrum from an unaged sample. This was taken to be evidence of chemical degradation. Proton MAS and the WISE exeriment gave some information about the nature of the water in the sample.     

互易性光学量对FMOCT输出光偏振态的联合影响

提出了用于大电流测量的法拉第镜式光学电流互感器方案.采用琼斯矩阵分析了互易性光学量联合作用对法拉第镜式光学电流互感器输出光偏振态的影响,做了计算机仿真验证；利用椭率概念定量分析了输出偏振光的椭圆退化问题,计算了输出光椭率与互易性光学量的关系；在输出光的椭圆退化问题上与单层保偏膜式光学电流互感器方案进行了对比.结果表明,在互易性光学量联合作用的条件下,法拉第镜式光学电流互感器的输出光仍保持线偏振状态,这将改善由温度引起的互易性光学量变化对系统工作稳定性的影响.     

Faraday mirror-typed optical current transformers and its theoretical analysis

A Faraday mirror-typed optical current transformer (OCT) design with turn-back optical paths is proposed to overcome the harmful effects of the linear birefringence inside bulk glass current sensing head, which can double the sensitivity and improve the state of polarization of the system output. The theoretical analysis of the working principle, the simulation of the polarization state of the output light beam and the comparison between it and the OCT with polarization preserving total reflection (PPTR) layers are presented. The results show that this design has a good suppressing effect on the degeneration of the polarization state of the output light, which has certain reference significance on the performance improvement of the present bulk glass OCT, and the development of practical OCTs.     

三波片偏振态变换器误差分析

在相干光通信和高速光纤通信等领域,要求偏振变换器具有高的偏振变换精度。对由两个可独立旋转的λ／4波片和一个可独立旋转的λ／2皮片组成的三波片偏振变换器的偏振变换误差进行了详细的分析。利用二维几何方法推导出了由波片方位角误差造成的偏振变换误差模型,并进行了数值计算。研究结果表明,三波片不同的组合方式对偏振态的变换精度有影响。其中,λ／4 λ／2 λ／4组合具有最高的偏振变换精度,λ／2 λ／4 λ／4次之,λ／4 λ／4 λ／2的最差;经三种偏振变换器变换后偏振态的方位角的变换误差较大,变换后偏振态的椭率角的误差很小;三种偏振变换器都可以实现较高精度的任意偏振态变换。     

多路窄脉冲功率线路合成

介绍了传输线变压器的结构特点,对其进行了理论分析和实验研究。采用传输线变压器结构将每路幅度约为4.5 kV/50Ω的4路脉冲合成了幅度约8.8 kV/50Ω的脉冲,通过实验证实了采用多根传输线串并联方式构成的传输线变压器装置可以将多路窄脉冲进行线路功率合成。应用此类结构设计了一种紧凑的高压窄脉冲发生器,将36路8 kV/50Ω的脉冲合成了约46 kV/50Ω的脉冲。采用传输线变压器合成器,应确保各路输入脉冲的前沿抖动足够小和高精度同步。