【作者】 夏云峰；

【导师】 曾祥君；

【作者基本信息】 长沙理工大学 ， 电力系统及其自动化， 2008， 硕士

【摘要】 小水电和风力发电是重要的分布式发电(Distributed Generation,DG)技术,近年来发展迅速。配电网接入DG后,其结构和故障后的故障电流及电压分布发生改变。小水电一般采用多台发电机并列运行;定子绕组单相接地故障是发电机最常见的故障类型,现有保护方法难以有选择性地检测故障点位置,判断故障发电机。风电场一般处于比较薄弱的电网末端,有功出力随风速随机变化,输电电缆和输变电设备消耗的无功功率也随之变化,影响风电场和互联电网的无功潮流和电压稳定。论文研究了分布式发电系统接地保护与无功补偿技术。针对配电网接入DG后的单相接地保护问题,通过分析接入DG的配电网各相电流故障分量特征,提出了基于对地计算电阻的单相接地保护方法,由故障相电压和相间差电流故障分量计算接地故障电阻。EMTP仿真分析结果表明该保护方法不受中性点接地方式和DG容量及接入位置的影响,具有较高的保护精度,灵敏度和鲁棒性。针对并列运行发电机定子单相接地保护问题,利用对地泄漏电流的基波和三次谐波故障分量相间差检测故障点,判断故障发电机,实现100%定子接地保护。EMTP仿真分析表明该保护方法适用于各种中性点接地方式且不受发电机运行工况影响,具有灵敏度高和鲁棒性强等优点。针对风电场无功-电压稳定问题,建立风电场多目标无功优化补偿模型,提出适用风电场内部电网的潮流计算方法,利用模态电压法确定风电场无功补偿点,运用改进遗传算法求解无功优化补偿模型,确定各补偿点最优补偿容量。理论分析和MATLAB仿真计算表明无功优化补偿模型及其求解模式的合理性和正确性。该无功补偿技术在合理的投资范围内降低了风电场网损,提高了风电场电压稳定水平。更多还原

【Abstract】 Small hydroelectric power plant and wind farm are typical forms of Distributed Generation (DG), have developed rapidly in the recent years. With the increasing penetration of DG, the topology configuration of distributed networks (DN) is changed, as well as the distribution of fault current and voltage. More than one generator directly connects to a common bus in a small hydroelectric power plant, which is defined as a multi-generator-system (MGS). Hydroelectric generators are often subjected to grounding faults in their stators. It is difficult to detect the fault location and the fault generator in the MGS by traditional stator grounding protection schemes. Wind farms generally lie in the terminal of power grid. The active power output of wind turbine generators varies along with the wind whose speed changes randomly. The reactive power absorbed by power equipments and cables is also varied, So that the reactive power flow and voltage stability of the DG system will be influenced.The schemes of grounding protection and reactive compensation for DG are studied in this thesis. In order to improve the grounding protection of DN with DG, a novel grounding resistance based single-phase grounding protection scheme is proposed. The grounding resistance is calculated by the faulted phase voltage and the fault component of phase currents difference. EMTP simulation results show that the protection scheme can detect the faulted feeder with high precision, and without influenced by neutral point grounding methods, the capacity and location of DG. In order to detect the generator with stator winding single-phase grounding fault in MGS, two protection schemes with the fundamental and the third harmonic fault components of the stator winding leakage current are proposed respectively. EMTP simulation results show that the protection scheme can detect the generator with grounding faults in the total (100%) stator winding and the condition of all kinds neutral grounding methods with high sensitivity and selectivity. In order to improve the reactive power-voltage stability of wind farms, a multi-objective optimal reactive power compensation model and a power flow calculation method are proposed. Modal voltage analysis is used to determine the candidate installation locations of the reactive compensation devices, and the improved genetic algorithm (GA) is applied to solve the reactive power compensation model and cuaculate the best compensation capacity. MATLAB simulation results show that the proposed scheme is with rationality and validity. The reactive power compensation techniques reduce power loss and improve voltage stability with rational investment.更多还原