直流偏磁对电流互感器的影响分析

发布时间：2019-04-11 13:36

【摘要】：高压直流输电等能源互联技术,是清洁能源大规模接入和远距离运送的重要技术保障。高压直流输电技术具有远距离、大容量等许多优点,随着高压直流输电技术的迅猛发展,越来越多的问题也随之而来。目前来看,交流电网中存在的直流分量问题就显得日益突出。电磁式电流互感器是电力系统中十分重要的电力设备,它直接关系着电力系统的继电保护的可靠运行和电能计量的精确性。而直流偏磁效应会给电流互感器带来严重影响,因此研究和分析直流偏磁对电流互感器的影响就具有十分重要的意义。论文首先通过直流偏磁等效模型和电流互感器T型等效模型的建立,详细分析了直流偏磁对电流互感器的影响。对于保护用电流互感器,它的作用是将系统的非正常状态或故障状态信息传送到继电保护装置,所以必须重点关注它的暂态饱和特性。通过理论分析故障后电流互感器励磁电流和磁通的关系,分析了直流偏磁和剩磁对电流互感器起始饱和时间的影响。其次,通过仿真实验进一步验证了直流偏磁对保护用电流互感器的影响。通过电流互感器基本磁化曲线的模拟,利用MATLAB中Simulink仿真组件,搭建出电流互感器的仿真模型研究其暂态饱和特性。研究表明正向的直流偏磁会加速电流互感器的饱和,而反向的直流偏磁延缓电流互感器的饱和,并且随着直流分量的加入,励磁电流波形发生畸变,偶次谐波尤其是二次谐波增加明显。再次,差动保护是变压器的主保护,而最常见的差动保护制动原理就是根据二次谐波制动。通过仿真分析出直流偏磁下,电流互感器饱和二次谐波含量增大,很容易导致继电保护装置拒动,影响电力系统安全。最后,对于计量用电流互感器,它的作用是将系统正常运行时的电流传送到测量设备,所以应该重点关注其稳态传变特性。通过理论分析推导出电流互感器误差受铁心磁导率的影响,再根据铁心磁导率和铁心电感之间的关系设计实验,测量直流偏磁下铁心磁导率的变化。通过交流、直流混合的实验方法,分析直流偏磁对计量用电流互感器造成的误差影响。实验结果证明,随着直流分量的增大,铁心磁导率减小,电流互感器误差增大,角差和比值差都明显增大。
[Abstract]:Energy interconnection technology such as HVDC transmission is an important technical guarantee for large-scale access and long-distance transportation of clean energy. HVDC technology has many advantages, such as long distance, large capacity and so on. With the rapid development of HVDC technology, more and more problems follow. At present, the problem of DC component in AC power grid is becoming more and more prominent. Electromagnetic current transformer is a very important power equipment in power system. It is directly related to the reliable operation of relay protection in power system and the accuracy of electric energy measurement. The DC bias effect will bring serious influence to the current transformer, so it is of great significance to study and analyze the effect of DC bias on the current transformer. Firstly, the influence of DC bias on current transformer is analyzed in detail through the establishment of DC bias equivalent model and T-type equivalent model of current transformer. For the protection current transformer, its function is to transmit the abnormal state or fault state information of the system to the relay protection device, so we must pay more attention to its transient saturation characteristics. The relationship between excitation current and flux of current transformer after fault is analyzed theoretically, and the influence of DC bias and remanence on the initial saturation time of current transformer is analyzed. Secondly, the influence of DC bias magnetic field on protection current transformer is verified by simulation experiment. By simulating the basic magnetization curve of the current transformer and using the Simulink simulation module in MATLAB, the simulation model of the current transformer is built to study the transient saturation characteristics of the current transformer. It is shown that the forward DC bias can accelerate the saturation of the current transformer, while the reverse DC bias will delay the saturation of the current transformer, and the excitation current waveform will be distorted with the addition of the DC component. The even-order harmonics, especially the second-order harmonics, increase obviously. Thirdly, differential protection is the main protection of transformer, and the most common braking principle of differential protection is based on second harmonic braking. Through simulation, it is found that the saturation second harmonic content of current transformer increases under DC bias, which can easily lead to the failure of relay protection device and affect the safety of power system. Finally, for the metering current transformer, its function is to transmit the current of the system under normal operation to the measuring equipment, so we should pay more attention to its steady-state transfer characteristics. Through theoretical analysis, it is deduced that the error of current transformer is affected by the permeability of core, and then the experiment is designed according to the relationship between core permeability and core inductance, and the change of permeability of core under DC bias is measured. The error effect of DC bias on measuring current transformer is analyzed by means of alternating current and direct current mixing experiment. The experimental results show that with the increase of DC component, the permeability of core decreases, the error of current transformer increases, the angle difference and ratio difference increase obviously.
【学位授予单位】：兰州理工大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TM452

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