【作者】 陈金玲；

【导师】 李红斌；

【作者基本信息】 华中科技大学 ， 电力系统及其自动化， 2007， 博士

【摘要】 光学电流互感器(OCT)具有绝缘性能好、频带范围宽、动态范围大、体积小、重量轻等优点,被认为是传统电磁式电流互感器(CT)的理想替代品。OCT经历了几十年的发展,仍未能在电力系统中得到大面积的推广应用,其主要原因是OCT的性能容易受环境因素如温度、振动等的影响,在长期运行过程中往往表现出相对时间的长期漂移。本文针对OCT易受环境因素影响的特点,提出了一种新型的基于比较测量法的光学电流互感器(以下简称比较式OCT)。比较式OCT在原有OCT的基础上引入了一个参考磁场,通过将被测电流磁场与参考磁场进行比较,得到与环境温度无关,仅与被测电流磁场的大小有关的最终测量结果。这种方法对传感头内部的线性双折射和传感材料的Verdet常数同时进行了补偿,具有从前的OCT补偿方法所不具备的优点。本文首先论述了比较式OCT的传感机理,对比较式OCT实现有效补偿的过程进行了理论论证。在此基础上,设计了比较式OCT的传感头结构。设计时着重考虑了光路设计和磁路设计两方面,确定了以条状玻璃构成、空间上相互垂直、两传感臂相互独立的光路结构,以及测量磁场与参考磁场相互正交,参考臂有效路径上的平均磁场尽可能大的磁路结构。同时为了克服条状传感头对位置的敏感性,设计了传感头固定装置。然后研究了比较式OCT的解调过程中需要解决的两个关键问题——直流磁场的精确解调和交流微弱信号的精确检测。针对参考直流磁场的精确解调,设计了双输入双输出的解调方法。该方法无论是对交流磁场还是对直流磁场都可以实现精确解调,还可以消除光路、电路的不一致以及光源波动带来的测量误差,是对从前解调方法存在的缺陷的改善。针对交流微弱信号的检测,摒弃了以前模拟解调的方法,设计了基于高精度数据采集卡和LabVIEW平台的全数字化解调系统,大大提高了比较式OCT整体的准确度和稳定性。接着,对比较式OCT的性能进行了理论分析和计算。比较式OCT可以看作是直流测量系统和交流测量系统的集成,这两个系统都经历了传感、光电转换、信号采集和解调计算四个主要过程。对主要过程中各个非理想因素对交流系统和直流系统的影响分别进行了分析和计算,得到传感头起偏器和检偏器之间的夹角偏离45°是比较式OCT的主要系统误差之一的结论,并针对该系统误差提出了改进措施。最后对比较式OCT进行了较系统的试验研究。试验研究包括了设计试验和比较试验两大部分。设计试验为传感头结构的合理设计提供了帮助,具体包括磁路设计试验和参考磁场受交流磁场影响试验。比较试验通过灵敏度比较、误差比较、抗干扰性能比较、温度性能比较及抗光源波动影响比较等一系列较系统的试验,对普通块状OCT和比较式OCT各方面性能进行了比较,一方面证实了比较式OCT结构设计的合理性,双输入双输出解调方法的优越性,另一方面也证实了基于比较测量法这种补偿手段的有效性,它使OCT抗环境因素干扰的能力特别是温度特性得到了很大的改善。更多还原

【Abstract】 Optical current transformer (OCT) is regarded as a perfect substitute for traditional current transformer because of its inherent advantages such as high electrical insulation, broad frequency band, large dynamic range, small volume, light weight and so on. However, OCT is not popularized in electrical power system yet after several decades’development. The main reason is that OCT is sensitive to external environment factors such as temperature, vibration et al. A gradual sensitivity drift happens in its long-term outdoor running.A novel OCT based on comparative measurement is proposed to compensate the sensitivity drift of ordinary OCT. The OCT based on comparative measurement introduces a permanent magnetic field as the reference, an eventual result can be obtained which is irrelevant to environment factors but only proportional to the magnetic field intensity caused by the primary current. The comparative OCT compensates both the linear birefringence that exists in the sensor head and variety of Verdet constant of sensing material. In a word, the comparative OCT has more advantages than other OCT compensation schemes.The sensing principle of comparative OCT is expounded firstly. And based on the principle, the structure of comparative OCT’s sensor head is designed. The light path design and the magnetic path design are the two most important hands. The eventual light path is structured by two independent, perpendicular strips of glass. And the magnetic path design make that the measured current magnetic field is vertical to the reference magnetic field, also the average magnetic intensity is as much as possible. At the same time, a pair of tongs is designed to fix the relative position between the primary conductor and the sensor head, thus the measuring result of the OCT made up of strips of glass is repeatable.Then, two key problems in signal demodulating are pointed out. One is the right demodulating of reference DC magnetic field. The other is the accurate detecting of weak modulated signal. A dual-input and dual-output demodulating scheme is applied to solve the former problem. This demodulating scheme makes up for the shortages of former schemes. It can demodulate both AC magnetic field and DC magnetic field accurately, and can eliminate the error caused by the unbalance of light path or circuit and the fluctuation of light intensity. In order to detect the weak modulated signal accurately, former analog demodulating system is replaced by an all-digital demodulating system, which is in fact a virtual instrument based on a high accurate data acquisition card and LabVIEW graphic language. The all-digital demodulating system benefits the accuracy and stability of the comparative OCT greatly.The comparative OCT is the integration of a DC system and an AC system. Both of them include four main parts: sensing, O/E transversion, sampling and demodulating. Every possible error source in these parts is respectively analyzed in each system. The conclusion that, the departure from 45°of included angle between the polarizer and the analyzer is one of the main system errors of the comparative OCT, is obtained. Some measures are taken for decreasing the error.At last, a series of tests including design tests and comparing tests are carried out. The design tests tend to provide helps for the sensor head structure design. The comparing tests including sensitivity, error and temperature comparing verify the superiority of the dual-input and dual-output demodulating scheme and the effectiveness of the compensation method based on comparative measurement. The performance relative to environment factors of the comparative OCT is much better than the ordinary one.更多还原