摘要
在电力系统中,各种谐波源产生的谐波影响着整个电力系统的电气环境,对电气设备的危害是严重的。随着电力电子等设备的迅速发展,谐波问题也越来越受到人们的重视。变压器是传统的谐波源之一,在正常情况下,其产生的谐波不大,但当变压器工作在一些特殊运行方式,如在夜间负荷低谷时段,电网运行电压偏高的情况下,变压器铁芯饱和程度增加,其产生的谐波电流急剧增大,由此反映的就是电网在负荷低谷时段谐波电压过高的现象,在小电网中尤为明显,已经大大超过了我国的谐波标准。因此,对小电网负荷低谷时段谐波电压过高问题的研究具有十分重要的意义。
本文对多个变电所实测数据进行了统计分析,总结了电网在负荷低谷时段谐波电压的一些特征。采用专业的电磁暂态仿真软件EMTDC研究影响变压器谐波电流的因素,其变压器模型采用基于磁路模型原理的UMEC变压器模型,该模型具有较高的仿真精度,并利用MATLAB软件对仿真数据进行了处理分析,与实测数据进行了对比分析。
通过大量分析与仿真得出以下主要结论:变压器谐波电流的大小主要与变压器铁芯的饱和程度有关,影响变压器铁芯饱和程度主要是电压大小和变压器选取额定磁密的大小,变压器铁芯随电压升高饱和程度增加,选取额定磁密大的变压器则加剧饱和程度的增加;因为输电距离长和电源短路容量小,小电网在轻载或空载时会使电网末端电压的升高的幅度较大,而且电网在负荷低谷时段经常会有未切除的电容器组,使电网的谐波阻抗呈容性,可能会出现谐波放大的现象。
In power system, the harmonic which is produced by various kinds of harmonic sources is influencing the electric environment of the whole power system, the danger resulted from this to the electric equipments is serious. With the rapid development of equipment such as the electric electron, the question of harmonic is paid more and more attention to by people. The transformer is one of the traditional harmonic sources, in normal cases, the harmonic it produced is not large, but when the transformer is working in some special operation ways, for example, in the valley period of load during the night, under the voltage of power networks operating on higher situation, the iron core saturation degree of the transformer increases, the harmonic of excitation current it produced increases sharply, therefore, the phenomenon it reflected was that the harmonic voltage of valley period of load in power networks is too high, it is particularly obvious in the small power networks, which have already exceeded the harmonic standard of our country greatly. So, it is much meaningful to research the problem that harmonic voltage is too large on valley period of load in the small power networks.
This paper carried on statistical analysis to the data of measurement on a lot of substations, has summarized some characteristics of the harmonic voltage on power networks valley period of load. Taking the specialized electromagnetism transient software EMTDC to study the factors influencing the harmonic current of transformer, and the transformer model adopts UMEC transformer model based on magnetic circuit model principle, for this model has higher precision, this paper also utilizes MATLAB software to deal with analyzing to the emulation data, which was compared and analyzed with the data of measurement.
Through a certain amount of between analysis and emulation the paper can get some main conclusions. Harmonic current of transformer mainly relates to saturation degree of the iron core of the transformer, which influences saturation degree of iron core main include the size of the voltage and affects transformer choosing the size of rating magnetic flux density, transformer iron core saturation degree rises while voltage increases, the larger rating magnetic density transformer aggravates the increasing saturation degree; Because of long distance transmission line and little capacity of short circuit, small power networks will make the voltage in the end of power networks rise heavily when on unload or light load, and often there are capacitance banks not removal, which makes the harmonic impedance of the power networks present the capability, may lead to the harmonic amplification phenomenon.
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