【作者】 高艳；

【导师】 刘沛； 林湘宁；

【作者基本信息】 华中科技大学 ， 电力系统及其自动化， 2009， 博士

【摘要】 材料科学与制造技术的进步拓展了高压交联聚乙烯(Cross Linked Poly Ethylene，XLPE)电缆的应用领域，促成了高压发电机(Powerformer)的发明，这是发电技术发展史上的一次显著变革。高压发电机能够直接与高压母线相连，与传统发电机相比，高压发电机有望提高系统可靠性、稳定性，提高能量转换效率，减少电厂占地面积。而高压发电机继电保护问题的解决和相关稳定性问题的深入研究将推动这种新型发电技术的进步和推广。论文针对上述问题开展研究，具体工作如下：高压发电机在系统中处于重要地位，其定子绕组单相接地故障保护需满足高灵敏度、覆盖100％定子区域的要求。论文基于高压发电机内部故障仿真模型，分析了高压发电机发生定子绕组单相接地故障时的电气特性，提出了一种基于零序能量的高压发电机定子单相接地保护新原理。该保护原理利用高压发电机机端零序电压和零序电流获得零序功率和零序能量，通过分析能量方向检测接地故障，实现对发电机区内故障和区外故障的区分。为了减小发电机的体积，高压发电机的绝缘系统在设计上采用分级绝缘方式，中性点侧的绝缘强度相对机端较弱。当其运行在非全相异常工况时，中性点将承受很高的过电压，绝缘受到严重威胁。论文在分析高压发电机非全相运行状态特点的基础上，提出了一种基于高压发电机机端零序电压和定子绕组负序电流、并借助断路器辅助触点信息进行判断的高压发电机非全相运行保护方案，并通过PSCAD/EMTDC建立系统模型，对方案进行仿真验证。高压发电机与高压母线直连，当多台高压发电机并列运行时，若其中一台发生励磁系统故障导致过电压，利用简单的过电压保护无法实现选择性动作。论文利用发电机机端电压和无功功率输出之间的关系，提出了一种改进的并列运行高压发电机过电压保护方案。该保护方案除检测过电压故障外，还通过发电机无功功率输出的变化量识别引发过电压的根源。采用补偿系数修正保护的动作时间，保证对母线过电压影响最大的发电机能最先被切除，该保护方案的应用领域并不局限于高压发电机，亦可为直接并列运行的普通发电机提供选择性过电压保护。论文研究了传统发电机高压侧电压控制(HSVC)原理，基于此对HSVC提高电力系统暂态功角稳定性的能力进行分析。由于高压发电机能够直接与高压母线相连，无需增设HSVC模块即可很方便地控制高压母线的电压。论文采用高压发电机实现高压侧电压控制，利用电力系统综合程序(PSASP)建立单机-无穷大系统及改进的EPRI-7节点系统，通过与传统发电机AVR和传统发电机HSVC励磁控制的比较，分析了高压发电机电压控制改善电力系统暂态功角稳定性的效果。论文研究了电压稳定性的基本理论、提高电力系统暂态电压稳定性的措施及高压发电机的过负荷特性。在此基础上，采用PSASP建立了EPRI-36节点系统仿真模型，通过与传统发电机AVR和HSVC励磁控制的效果比较，分析了高压发电机电压控制改善电力系统暂态电压稳定性的作用。论文最后对上述研究结果进行总结，提出进一步研究的方向。更多还原

【Abstract】 The applications of XLPE (Cross Linked Poly Ethylene) cables have been widely extended due to the developments of material science and manufacturing techniques. One of the significant events is the invention of Powerformer. This means a remarkable revolution in the developing history of generation technology. Powerformer can be connected directly to the High-Voltage (HV) busbar; therefore, compared with conventional generators, Powerformer can improve the system reliability and stability, increase the conversion efficiency and reduce the occupied area of generation plants. There is no doubt that the solution of its relay protection problems and the intensive research of its corresponding stability problems are promising to promote the advancement and the popularization of this novel generation technology. Therefore, the research topics of this dissertation focus on the above problems, and the details of it are as follows:Powerformer plays an important role in power systems, so the protection of stator single phase-to-ground fault should have high sensitivity and 100% coverage. On the basis of the internal fault simulation model of Powerformer, the electrical characteristics of it on the occurrence of a stator single phase-to-ground fault are analyzed and a zero-sequence energy based novel protection scheme for stator single phase-to-ground faults is proposed. This protection scheme requires the measurements of the zero-sequence voltage and the zero-sequence current from the terminal of Powerformer to formulate zero-sequence power and zero-sequence energy. By means of the analysis of the direction of zero-sequence energy, the internal faults and the external faults can be distinguished.In order to reduce the volume of the Powerformer, the insulation system of it is designed in a graded way, and the insulation intensity of the neutral is comparatively weaker. When the Powerformer is operating in the condition of open-phase, the neutral will endure very high voltage, which will have seriously negative impact on the insulation of the Powerformer. Based on the analysis of the characteristics of open-phase operational state, a novel open-phase protection scheme utilizing the zero-sequence voltage of the terminal and the negative-sequence current of the stator windings is proposed. A simulation model is set up using EMTDC, and intensive simulations are carried out to verify the protection scheme.Powerformer is connected to HV busbar directly. Hence, for a group of Powerformers operating in parallel, if one of them encounters excitation failure and leads to the scenario of overvoltage, all the Powerformers will be isolated without selectivity by the simple overvoltage protection only relying on the same fixed time delay. On the basis of the analysis of the relationship between the terminal voltage and the reactive power of a Powerformer, a new overvoltage protection scheme is put forward in this dissertation. In addition to the detection of overvoltage condition, this protection can also identify the source of overvoltage by virtue of the variety of reactive power. A compensated voltage factor is used to modify the operating time of the protection. In this case, the generator which has the most vital impact on the overvoltage of the busbar will be tripped firstly. Then, the protections of the sound Powerformers will drop off due to the removal of the disturbance source. The application of this protection scheme includes but is not restricted to Powerformer, which can also provide the selective overvoltage protection for conventional generators working in parallel.The principle of High side voltage control (HSVC) of conventional generators is studied in this dissertation. On the basis of that, its ability of improving transient angle stability of power systems is analyzed. Because of the direct connection to the HV busbar, the Powerformer can control the voltage of the HV busbar without adding a HSVC module. In this dissertation, the Powerformer is initially utilized to realize HSVC excitation control. A single-generator-infinite-system model and an EPRI-7 nodes system model are set up by virtue of PSASp (Power System Analysis Software Packet). Compared with the controlling effects of the conventional generator AVR and conventional generator HSVC excitation control, the ability of Powerformer voltage control of improving transient angle stability of power systems is analyzed.The fundamental theories of voltage stability, the countermeasures of improving transient voltage stability and the overload characteristic of Powerformer are studied in this dissertation. After that, an EPRI-36 nodes system is set up by virtue of PSASP. Compared with the controlling effects of conventional generator AVR and conventional generator HSVC excitation control, the ability of Powerformer voltage control of improving transient voltage stability of power systems is analyzed.Finally, conclusions are made and further work worth lucubrating is outlined.更多还原