基于暂态拟合制动特性的发电机差动保护算法

从电流互感器饱和励磁电流和发电机差动保护工作点随时间变化特点分析入手,提出了一种基于暂态拟合制动特性原理的差动保护算法。算法通过拟合电流互感器饱和时差动不平衡电流随时间变化规律得到制动曲线斜率K随时间变化曲线,给出了初始K值曲线表达式及初始K值曲线的调整方法。该制动特性既反映了电流互感器饱和暂态过程引起的差动不平衡电流随时间变化的规律,又兼顾电流互感器正常传变时的稳态误差,使得保护动作门槛值在区外故障电流互感器饱和暂态过程中能够包络差动不平衡电流,增加了保护的可靠性。同时电流互感器正常线性传变时间段K值曲线的值可低于传统比率制动差动保护制动曲线斜率值,保护更加灵敏。理论分析和仿真结果表明,算法比传统比率制动差动保护有更好的区外故障抗电流互感器饱和能力和区内故障的灵敏性。

Transient Fitting Restraint Characteristic Based Generator Differential Protection Scheme

With an analysis of the change of excitation current for a current transformer with time and the change of operating characteristic for generator percentage differential protection with time when there is an external fault with current transformer saturation, this paper proposes a generator differential algorithm based on transient fitting restraint characteristic. The algorithm fits the slope K of restraint curve with the change of transient unbalanced current with time during current transformer saturation. The initial expression of slope K curve and its adjustment method are proposed. The proposed transient fitting restraint characteristic reflects both the transient unbalanced current characteristic with time during current transformer saturation period and the stable current transformer error characteristic enabling the operating threshold to envelop the unbalanced current to increase protection reliability. Meanwhile the restraint characteristic only needs to consider current transformer stable error when current transformer is working in linear condition and the slope K can be set lower than traditional percentage differential protection which makes this algorithm more sensitive than the traditional one. Theoretical analysis and simulation results based on MATLAB indicate that the algorithm proposed has better reliability during external faults with current transformer saturation and higher sensitivity during internal faults than traditional percentage differential protection. This work is supported by National Natural Science Foundation of China (No. 50977012, No. 51377022) and Graduate Research and Innovation Project of Jiangsu Province (No. KYLX_0122).