【作者】 毕大强；

【导师】 王祥珩；

【作者基本信息】 清华大学 ， 电气工程， 2003， 博士

【摘要】 定子绕组单相接地故障是发电机最常见的一种故障，而且往往是更为严重的绕组内部短路故障发生的先兆，定子绕组单相接地保护的可靠与灵敏动作可以大大降低内部短路故障的发生几率，减少故障造成的损失。定子绕组单相接地保护是大型发电机继电保护系统中十分重要的一项内容，而现有保护方案难以满足目前大型水轮发电机（如三峡电站机组等）不断提高的定子绕组单相接地保护灵敏度要求。为了详细分析大型水轮发电机定子绕组单相接地故障特点，校验和开发相应的保护方案，本文建立了以交流电机多回路分析方法为基础、考虑定子绕组对地电容、采用实际绕组结构的发电机定子绕组单相接地故障仿真模型。通过修改故障电导矩阵，实现单相接地故障和其它类型故障的仿真分析。针对目前大型水轮发电机定子绕组单相接地保护灵敏度偏低的问题，通过分析单相接地故障后机端和中性点零序电压的变化特点，提出了一种基于机端和中性点三次谐波电压故障分量和两种基于机端和中性点零序电压故障分量的高灵敏度、高可靠性保护方案，并实现定子绕组的100%保护。分析噪声对现有基于小波变换模极大值的定子单相接地保护的影响，提出了灵敏度高、抗干扰的基于小波变换多尺度滤波的能量法保护方案。将所建数学模型推广到多台发电机扩大单元接线方式，分析此种接线方式下单相接地故障引起的暂态零序电压和电流变化特点，提出了基于小波变换的选择性单相接地保护方案。为准确计算接地故障的过渡电阻值，分析了中性点接地装置参数对外加电源型定子单相接地保护中导纳判据的影响。分析了发电机中性点经消弧线圈接地时，其参数的选取及对基波零序电压保护的影响。在多台动模机组上做了大量相关试验，验证了本文所提出数学模型的正确性和有效性以及保护方案的灵敏度与可靠性。更多还原

【Abstract】 The ground faults in the generator stator are by far common faults to which generators are subjected. Internal short-circuit faults, which may immediately damage generator, are always preceded by the ground faults. The possibility of internal fault and damages caused by it can be decreased largely if the stator ground fault protection reliably and sensitively operates. Therefore, the stator ground fault protection plays an important role in the protection system of generator. At present, the large-sized hydro-generators, such as the generators in Three Gorges Power Station, require that the stator ground protection must be with very high sensitivity, so that it is beyond the capacity of available protection schemes.In order to analyze the characteristics of stator ground fault and develop its protection schemes, a mathematical model for large-sized hydro-generators is established based on the multi-loop theory of AC machines and considering the capacitance to ground and actual construction of the stator windings. Modifying the fault-conductance matrix can simulate the ground faults and other kinds of fault in the stator windings.To resolve the situation that the sensitivity of present ground fault protection schemes is low for the large-sized hydro-generators, a kind of protection scheme based on the fault component of third-harmonic voltage and two kinds of protection scheme based on the fault component of zero-sequence voltage at the terminals and neutral are developed, and they can obtain higher sensitivity and reliability and provide 100% protection for the stator windings.The influence of noise on the stator ground fault protection based on the local modulus maximum of wavelet transform is analyzed. To overcome the adverse effect of noise, a new kind of spectral energy protection scheme with high sensitivity and anti-interference is put forward in the thesis by using the multi-scale filter of wavelet transform. Further, extending the simulation model to<WP=7>the large unit-connected generators, a selective protection scheme is presented by analyzing the characteristics of the variation of zero-sequence transient voltage and current caused by ground faults at different locations.To accurately calculate the value of grounding transient resistance, the thesis compares and analyzes the effect of the equivalent parameters of grounding equipment at the neutral on the admittance criterion of injecting sub-harmonic voltage. In addition, choosing the different value of inductance and resistance of Petersen-coil at the neutral may influence the operation performance of the zero-sequence fundamental frequency voltage protection.A large number of experiments on different generators verify that the mathematical model is correct and effective, and that the protection schemes are sensitive and reliable.更多还原