【作者】 吴昊；

【导师】 姚建刚；

【作者基本信息】 湖南大学 ， 电气工程， 2012， 硕士

【摘要】 35kV中性点不接地系统中，广泛采用电磁式电压互感器（PT），在系统断路器操作或者发生故障引起一系列电磁暂态过程中，PT由正常工作状态进入饱和状态，当PT的电感参数与系统中的电容参数相匹配时，就会发生铁磁谐振，铁磁谐振过电压严重影响了整个系统的安全稳定运行。目前虽有多种抑制铁磁谐振的措施，但是由于不同系统具有不同的接线方式和运行方式，以及铁磁谐振现象的复杂性和随机性，使得各种抑制措施都有一定的局限性和适用范围，不能通用，也不能从根本上消除谐振。因此，必须针对具体的变电站系统进行铁磁谐振深入研究，通过对多种消谐措施的有效性和适应性分析比较，得出消谐措施抑制谐振过电压、过电流的规律，为实际工程中消谐措施的选择提供参考依据。本文首先通过试验得到35kV系统常用的PT的空载伏安特性曲线，采用逐点递推法将伏安特性曲线转化为磁链电流特性曲线，其次依据某典型35kV中性点不接地系统实际接线图，运用电磁暂态仿真计算软件（ATP-EMTP）建立系统仿真计算模型，在分析铁磁谐振产生机理的基础上，综合考虑多种铁磁谐振影响因素如系统运行方式、外界激发方式、单相接地故障点接地电阻值、单相接地故障消失时刻等，并进行计算与分析，研究得出其对铁磁谐振影响的规律。最后，本文对常用的消谐方法在该仿真系统中的适应性进行了定量分析比较。仿真计算结果表明：单相接地故障消失是配电网中最容易激发分频铁磁谐振的一种激发方式，现有的几种消谐措施都能够在一定程度上消除或者减弱谐振，但是都存在一定的优缺点和适用局限性。PT高压侧中性点经非线性电阻消谐器接地能够有效地抑制铁磁谐振，实际使用过程中应当注意非线性电阻的热容量要满足要求，以及开口三角的接地信号装置的可靠发信不受影响；采用4PT法抑制谐振时，会在闭口三角绕组产生较大的环流，进而烧坏PT；PT开口三角接入阻尼电阻抑制单相接地故障激发的谐振时，应尽量使电阻在单相接地故障消失后瞬间接入，同时选择合理的阻尼电阻值。针对本文所研究的接线方式和运行方式的系统，为了同时达到抑制由于单相接地故障消失而激发的频率较低的分频谐振过电压和PT高压侧过电流的目的，可以依次选用系统中性点经消弧线圈接地、PT中性点经非线性电阻消谐器接地、4PT法这三种方法，其中PT的开口三角形绕组接入阻尼电阻这种方法不能有效的抑制分频谐振所产生的流过PT高压侧绕组的过电流，而系统中性点经消弧线圈接地这种方法抑制过电流的效果最好。更多还原

【Abstract】 Potential transformers has been widely used in35kV neutral ungrounded system.PT can work in saturation state when the circuit breaker operating or the systemfaulting. If the inductance parameter of PT and the capacitance(such as the distributecapacitance of the network) parameter matched, the ferroresonance will be excited.The safe operation of the distribution network has been seriously threatened by theferroresonance. Although there are also several measures which have often been usedto avoid ferroresonance at the present time. The ferroresonance can’t be eliminatedcompletely because of the complexity and randomicity caused by different parameterand operation modes of different system, which make those suppressive measureshave some limitations. So it is necessary to do an further study on ferroresonancewhich aims at neutral ungrounded system. Through analysis and comparison onvalidity of diversiform measures that are Often used to eliminate ferroresonance, itcan summarize the law of suppression of overvoltage and overcurrent caused byferroresonance by measures used to eliminate ferroresonance, which providemeaningful evidence for choosing suitable measures to eliminate ferroresonace inpractical projects.In this thesis, the no-load voltage-current characteristic of three35kV PTs havebeen tested at first. Then the Progressive Deduction Method have been used to turnvoltage-current characteristic curve into magnetic flow-current charateristic curve. Asimulation model has been built based on a typical35kV neutral ungrounded systemprimary sides devices map by using Electromagnetic Transient Program(ATP-EMTP).Many influencing factors that affect ferroresonance have been summarized on thebasis of theory of Ferroresonance. Calculation and analysis have also been done toanalyze the impact of these factors. For example, operation modes of system, modesof outside excitation, grounding resistance at single-phase ground fault point, and soon. After that, calculation and analysis have also been done to summarize the law ofthe impact of those factors on ferroresonance. In order to conclude the law offerroresonance suppression by measures used to eliminate ferroresonance, theinstance of ferroresonance suppression by measures used to eliminate ferroresonancehave been quantitatively analysed and compared in this thesis. The simulation results show that most of the ferroresonance caused by saturationof PT in distribution network happen affter the disappearance of single-phase groundfault. The disappearance of single-phase ground fault can easily excite subharmonicferroresonance. Diversiform measures used to eliminate ferroresonance now caneliminate or suppress ferroresonance in a certain extent, but all of them have certainmerit, demerit and applicable scope. Connecting a nonlinear resistance eliminatorbetween the neutral point and high voltage side of PT and ground is a effectivemeasure to eliminate or suppress ferroresonance, the heat capacity of nonlinearresistance resonance eliminator and the corrtect action of the protection groundingsignal device should meet the requirement when this measure is used to suppressferroresonance that is especially caused by single-phase ground fault. A biggishovercurrent in closed delta winding may be engendered when4PT is used to suppressferroresonance. When connecting damping resistance to the broken delta winding ofhost PT is used to suppress ferroresonance caused by the disappearance ofsingle-phase ground fault, the resistance should be connected as soon as thesingle-phase ground fault disappears. To the primary sides devices map and operationmodel for the study system of this paper, These methods including connectingPetersen coil to the neutral point of system, connecting nonlinear resistance resonanceeliminator between the neutral point on high voltage side of PT and ground and4PTcan be choosed in turn to restrain the overcurrent and the overvoltage of the PTcaused by lower frequency subharmonic ferroresonance, the effect of connectingPetersen coil to the neutral point of network is the best. Connecting resistance orresonance device to the broken delta winding of host PT can’t effectively restrain theovercurrent of the PT caused by lower frequency subharmonic ferroresonance.更多还原