Effect of Modulation Error on All Optical Fiber Current Transformers

For actively modulated In-line Sagnac interferential all optic fiber current transformers (AOFCTs), the accuracies are directly affected by the amplitude of the modulation signal. In order to deeply undertand the function of the modulator, a theoretical model of modulation effect to AOFCTs is built up in this paper. The effect of the amplitude of the modulation signal to the output intensity of AOFCTs is theoretically formulated and numerical calculated. The results show that the modulation voltage variation could affect the output accuracies significantly. This might be some references on the investigation for practical applications of AOFCTs.

Design and applicability analysis of independent double acquisition circuit of all-fiber optical current transformer

The advantages of the all-fiber optical current transformer include but are not limited to being small in size,having no magnetic saturation,exhibiting high measurement accuracy,and boasting strong electromagnetic interference resistance.However,the high cost of the all-fiber optical transformer limits its promotion and application in engineering.This paper proposes a design scheme of an independent double acquisition loop for the all-fiber optical current transformer based on the single optical path.Firstly,based on the closed-loop control mode and open-loop control mode,the twochannel sampling signal demand for relay protection,and the independent dual-acquisition loop design scheme of the all-fiber optical current transformer are proposed.Secondly,the reliability and economic feasibility of the scheme are demonstrated by an analysis of system failure and cost.The results show that the scheme can actualize the acquisition function of two independent all-fiber optical current transformer products on a single all-fiber current transformer in an integrated manner,which greatly reduces the cost of the all-fiber optical current transformer in engineering applications.

Optically Driven Current Transformer with Optical Fiber Data Link

An optical fiber transmitting photoelectric coupling current transformer has been developed. In the environment of high voltage and electromagnetic fields, this device is characterized by high insulation, high reliability, small mass and high anti-interference. The structure design and operating principle of the system are introduced, measurement errors are analyzed and experimental results are given.

Optical fiber-based power and data delivery system for high voltage electronic current transformer

This paper describes a prototype power delivery system developed for high voltage electronic current transformer （ECT） that uses laser light to transfer power to and communicates with the primary converter. The design is based on optical-to-electrical power converters, solid-state diode lasers and optical fibers. Command signals are transmitted via the same up-fiber used to send power from secondary power supply to primary converter. The upward data transmission is completed during the brief interruption of power delivery without affecting steady power-supply. A simple comparator added to the primary converter can take the command data. Experimental results show that the fibers can provide reliable up-link for data transmission at 200 kb/s from the secondary to the primary converter. Based on the delivery system, the secondary converter can control three auxiliary channels to provide additional information. These monitoring channels are used in a time-multiplexing mode to provide information about the operation temperature, voltage and current at the remote unit for monitoring the ECT. This preventive maintenance or built-in test can increase reliability by giving early warning for necessary maintenance request.

Optical Design of OCT with Gapped Magnetic Ring

The mathematics and physics model of OCT (Optical Current Transformer) with a gapped magnetic ring is briefly discussed in the paper. And some proposals of how to select the magnetic materials and crystals and reduce the stress birefringence of the crystal are also put forward in the paper. Based on the above, an OCT with 1000 A rated current is designed by using the ANSOFT Maxwell tools.

AFOCT系统中敏感光纤器件的老化对系统测量准确性的影响

研究了全光纤电流互感器(AFOCT)系统中敏感光纤器件老化对系统测量准确性的影响。首先,基于法拉第磁光效应,采用琼斯矩阵建立AFOCT系统的传输模型;结合存在双折射的传感光纤的琼斯矩阵,给出系统的注入电流测量值的表达式。进一步,搭建了光学测试系统,实验表征传感光纤的双折射率;基于测试结果,对传感光纤的琼斯矩阵以及系统传输模型进行校准,以降低AFOCT系统注入电流的测量误差。最后,对传感光纤开展了相当于实际运行3个月的加速老化试验,并测试获得老化后传感光纤的双折射率。采用校准后的AFOCT系统传输模型,分析了老化后双折射率的变化对系统注入电流测量值的影响。实验结果表明,在传感光纤老化3个月之后,系统就已经产生了0.2955%的相对误差。

小波变换对OCT图像的降噪处理

通过分析光学相干层析成像系统中的噪音源以及不同噪音对成像质量的影响,利用小波变换的方法,结合软阈值滤波对图像去噪,消除噪音对图像的干扰,处理后图像变得清晰了,图像质量得以改善,表明该方法能达到减小图像噪音的目的·

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.

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.

基于序贯卡尔曼滤波的OCT信号处理方法研究

使用光学电流互感器(Optical Current Transducer,OCT)测量小电流时,测量得到的内部噪声信号往往大于光电信号,测得的读数不能正确反映电流的真实值。有效滤除噪声,提高信噪比是OCT信号处理的关键所在。介绍了基于法拉第磁光效应的光学电流互感器的基本原理和信噪特性,在被测电流为交直流混合信号的情况下,建立合适的滤波状态空间模型,采用序贯卡尔曼滤波的方法在Lab VIEW上进行仿真。结果表明序贯卡尔曼滤波算法能够对测量电流实时进行信噪分离,同时准确分离出交流和直流分量,提高了输出信噪比和测量精度。

基于一种新小波变换的OCT图像去噪方法

散斑在OCT图像中既是信息载体,也是一种严重的噪声。针对OCT图像的这一特点,提出一种基于小波变换和维纳滤波相结合的OCT图像去噪方法。通过对OCT图像进行小波分解,得到四个不同频带的子图像,保持低频部分不变,对另外三个高频细节图像进行维纳滤波,将低频子图像和三个滤波后的高频细节子图像进行小波反变换,得到去噪后的图像。实验结果表明小波变换和维纳滤波相结合的方法对OCT图像有比较理想的去噪效果。

双折射效应和去直流检测法的MOCT模型研究

基于双折射效应和去直流检测法,建立一种磁光式电流互感器(magneto-optic current transformer,MOCT)模型.该模型在一次侧电流检测部分,采用Jones矩阵建模,综合考虑Faraday效应和磁线振双折射效应;在二次侧转换器部分,建立去直流双光路检测法分析光强度信息.数值仿真和实验验证了MOCT模型的正确性.该模型考虑了磁光式电流互感器的光学检测特性,可为MOCT应用提供理论支持.

两个光学参量色散对光学玻璃OCT灵敏度的影响

以琼斯矩阵为数学工具,利用理论分析和计算机仿真的方法研究了单层保偏反射膜反射相移的色散特性和光学玻璃的Verdet常数色散特性以及它们对光学玻璃电流互感器灵敏度的综合影响。结果表明:这种影响可使互感器输出波动超出国家技术标准的要求。因此,应对光源采取恒温控制,并对光源驱动电流恒流控制或对系统输出结果采取补偿措施。

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.

反射相移对法拉第镜式OCT影响的理论研究

为了减小块状玻璃电流传感头中线性双折射与反射相移等互易效应产生的有害影响,提出了一种利用法拉第反射镜构成的具有折返传感光路的光学电流互感器方案.采用矩阵理论分析了该方案的光学工作过程,在不计线性双折射的条件下,当反射相移单独存在时,用仿真方法研究了反射相移对法拉第镜式光学电流互感器输出光偏振态的影响,并与单层保偏膜式方案进行了对比.结果表明,法拉第镜式光学电流互感器方案可以解决由反射相移引起的系统输出光偏振态椭圆退化问题,提高了光学电流互感器的灵敏度和温度稳定性.这对于改进现有块状玻璃电流互感器的性能、开发实用型光学电流互感器具有一定的参考意义.

减小无源OCT中初始双折射影响的方法

针对无源光学电流互感器的线性双折射问题,用琼斯矩阵分析了双折射对系统输出的影响。分析了输出光退化成圆偏振情况下光学电流互感器仍能传感电流的现象,以及输出光保持线偏振条件下系统输出电压仍受线性双折射影响的现象。分析了入射光偏转角、入射光相移与初始线性双折射对光学电流互感器输出的联合影响。结果表明,当初始双折射存在的情况下,随着入射光相移的变化,系统输出相对偏差存在极小值,且极小值对应的入射光相移随着初始双折射值而单调递增。由此提出增加入射光相移来减小初始线性双折射对系统输出影响的方法。用计算机仿真了理论计算结果,实验验证了这种方法的可行性。对改进无源光学电流互感器的性能、开发实用光学电流互感器具有参考意义。

基于OCT的输电线路故障暂态电流保护

光学电流互感器(OCT)解决了继电保护中传统电磁式电流互感器的饱和以及暂态精度低等问题。分析了输电线路故障高频暂态分量产生的原因,并根据光学电流互感器能够正确传变暂态分量的特点,分析了基于故障分量的单端暂态电流保护的原理。

基于斯托克斯向量的MOCT故障识别模型的研究

针对传统电磁电流互感器故障时因磁饱和造成继保误动或拒动现象,提出了一种磁光电流互感器(MOCT)快速识别故障发生及类型的方法。该方法以通过石榴石型MOCT的偏振光的三个斯托克斯分量作为特征量,建立支持向量机识别模型,模型核参数及惩罚参数由粒子群寻优选取。此建模方法仅与斯托克斯分量及故障电流等级有关,与线性双折射及环境变量无关,避免了温度等外界因素对识别的干扰。实验结果表明,识别模型受温度影响小,当训练完成的识别模型工作于不同的温度条件下时,识别误差保持在2%以内。运行中的MOCT可以依靠斯托克斯分量及该模型准确识别故障电流等级,迅速判别出故障类型,精度较其他识别方法更高。

改进的多尺度域变步长自适应算法在FOCT中的应用研究

为了更有效的提高光纤电流互感器FOCT(Fiber-Optical Current Transformer)的信噪比,在分析FOCT输出信号特性的基础上,结合变步长自适应算法和小波变换理论,提出一种针对处理FOCT输出信号的改进多尺度域变步长自适应滤波算法,并设计了一种基于Active X技术的变步长自适应滤波系统,通过该系统将改进算法与现有的变步长自适应算法进行了对比,结果表明此算法的收敛速度和稳态精度都得到了很大的改善。然后将此算法在FOCT中进行了应用测试,测试结果反映了该算法能有效提高FOCT的检测信噪比和抗噪声干扰能力。

Novel Fiber Optic Current Transformer With New Phase Modulation Method

Based on the transverse electro-optic effect of lithium niobate crystal,combined with polarizers and Faraday rotator,this paper presents a collinear closed-loop fiber optic current transformer with spatial non-reciprocity modulation method,and the feasibility of the scheme is verified by both the theoretical and experimental evidences.The detection scheme avoids the limitation of the transition time of the sensing fiber coil on the phase modulation frequency,improves the sensitivity and stability of the system,and reduces the volume and cost of fiber optic current transformer.The sawtooth wave modulation scheme is adopted to realize phase bias modulation and feedback modulation through phase shift of sawtooth wave to achieve closed-loop detection effect,which enhances the signal to noise ratio and simplifies demodulation mode.The experimental results show that the current ratio errors measured at room temperature range from 1%to 120%of rated current meet the requirements of national standard GB/T 20840.8-2007 and reach the accuracy level of 0.2S.The temperature stability of the current transformer is also tested,and the ratio error measured at the rated current does not exceed±0.2%in the range of-30℃to 50℃.