耦合线路电气特性分析与软件开发

发布时间：2018-07-13 14:04

【摘要】：输电线路在电网中的地位不言而喻,土地资源的日益紧张给输电线路建设带来了新的变化：一是电力电缆的大规模应用,二是架空线共用走廊越来越常见。这两个场景会分别带来多导体线路耦合问题。电力电缆运行过程中,由于电磁耦合,电缆线芯会在护套上感应出电流,进而引起护套损耗。而交直流线路共用走廊则使得交流线路在直流线路中感应出基波电流并对直流换流器带来不利影响。在耦合线路研究领域前人已经做了大量的工作并取得了许多成果,但是仍然存在着一些问题需要深入研究和解决。当前该领域的研究存在以下不足：(1)护套损耗计算方法不够理想；(2)对护套连接阻抗器降损策略的特性研究不够深入；(3)直流侧基频电流对MMC换流器影响的研究不足；(4)交直流耦合对LCC-MMC系统影响的研究尚属空白。针对上述几个问题,本文对耦合线路的建模和分析方法进行研究,主要内容如下：(1)研究快速精确的电缆护套损耗计算算法。在非解耦模型的基础上,通过递推公式使节点电压方程降阶。在不损失计算精度的前提下(误差0.1%),使电缆护套损耗计算速度提升80%以上。该算法适用于目前电缆工程中出存在的诸多护套连接方式。基于本算法,开发Windows下运行的护套分析软件。可以输出指定电缆结构和运行状态下的护套电流电压分布和护套损耗。(2)研究电缆结构对护套损耗的影响。在得到快速精确的护套损耗计算算法后,本文对护套降损策略进行了全面研究。从不同电缆护套连接方式入手,比较了单端接地、双端接地、交叉互联电缆的护套损耗。此外还研究了交叉互联电缆在交叉互联数不同和分段长度不均匀时的护套损耗。(3)系统性地研究了串联阻抗的降损策略。研究串联阻抗的相角和幅值对降损效果的影响。本文研究发现当串联阻抗的阻抗角为90°时(即串联纯电感)降损效果最好,同时护套上的电压也达到最小。针对研究算例,本文推荐了交叉互联数不同时的串联阻抗幅值。(4)研究直流侧基频电流对MMC换流器的影响。在时域中推导了给定直流侧基频分量下交流侧出现的直流偏置公式。公式的计算结果与PSCAD的仿真结果高度一致。从公式中可以看出,MMC交流侧的直流偏置量小于同等条件下LCC交流侧的直流偏置量。(5)研究交直流耦合效应对LCC-MMC系统的影响。研究了耦合效应与交直流线路杆塔架设间距、并行架设长度、交流线路零序分量和交流线路故障状态之间的关系。交流输电线上的零序分量会明显增大耦合效应。在考虑零序分量的前提下,本文给出了交直流线路杆塔间距和并行长度之间应该满足的关系,为实际工程建设提供指导意见。
[Abstract]:The status of transmission lines in the power grid is self-evident, and the increasing shortage of land resources has brought new changes to the construction of transmission lines: first, the large-scale application of power cables, and second, the common corridor of overhead lines is becoming more and more common. These two scenarios will lead to the coupling problem of multi-conductor circuits respectively. During the operation of power cable, the cable core will induce current on the sheath because of electromagnetic coupling, which will cause sheath loss. The AC / DC common corridor induces the fundamental current in the DC line and has a negative effect on the DC converter. A great deal of work has been done and many achievements have been made in the field of coupling circuit research, but there are still some problems that need to be deeply studied and solved. The current research in this field has the following shortcomings: (1) the calculation method of sheath loss is not ideal; (2) the research on the characteristics of the loss reduction strategy of the sheathed impedance device is not deep enough; (3) the effect of DC side fundamental frequency current on the MMC converter is insufficient. (4) the effect of AC / DC coupling on LCC-MMC system is still blank. Aiming at the above problems, the modeling and analysis methods of coupling lines are studied in this paper. The main contents are as follows: (1) A fast and accurate calculation algorithm for cable sheath loss is studied. Based on the non-decoupling model, the nodal voltage equation is reduced by recursive formula. The calculation speed of cable sheath loss is increased by more than 80% without loss of calculation accuracy (0.1% error). This algorithm is suitable for many sheathed connection modes existing in cable engineering. Based on this algorithm, the software of sheath analysis running under Windows is developed. The sheathed current and voltage distribution and sheath loss can be outputted under the specified cable structure and operating state. (2) the influence of cable structure on sheath loss is studied. After the fast and accurate calculation algorithm of sheath loss is obtained, the strategy of sheath loss reduction is studied in this paper. Starting with different cable sheath connection modes, the sheathing losses of single terminal ground, double terminal ground and cross connected cable are compared. In addition, the sheathing loss of cross-connected cables with different interconnect numbers and uneven sectional length is studied. (3) the loss reduction strategy of series impedance is studied systematically. The effect of phase angle and amplitude of series impedance on the loss reduction effect is studied. In this paper, it is found that when the impedance angle of series impedance is 90 掳(that is series pure inductor), the loss reduction effect is the best, and the voltage on the sheath is also minimum. In this paper, the series impedance amplitudes with different cross interconnections are recommended for example. (4) the effect of DC base frequency current on MMC converter is studied. In the time domain, the DC bias formula for the AC side with a given fundamental frequency component of the DC side is derived. The calculation results of the formula are in good agreement with the simulation results of PSCAD. It can be seen from the formula that the DC bias of MMC AC side is smaller than that of LCC AC side under the same conditions. (5) the effect of AC / DC coupling effect on LCC-MMC system is studied. The relationship between the coupling effect and the distance between AC / DC line tower erection, the parallel erection length, the zero sequence component of AC line and the fault state of AC line is studied. The zero sequence component on AC transmission lines will increase the coupling effect obviously. On the premise of considering the zero-sequence component, the relationship between the distance between the poles and towers and the parallel length of the AC / DC transmission lines is given in this paper, which provides guidance for the practical engineering construction.
【学位授予单位】：浙江大学
【学位级别】：硕士
【学位授予年份】：2016
【分类号】：TM75

【相似文献】