一种微机型反时限过激磁保护的实现方法

Microcomputer-based inverse time-lag over-excitation protection

采用三相线电压的采样值计算过激磁电压的有效值,仿真结果表明该算法与系统频率无关,计算精度高。采用傅里叶变换计算出被测电压的实部或虚部值,并作为线性插值法的输入值,查找与实部或虚部值相邻的2次过零点的时间差,计算系统的周期和频率。仿真结果表明该算法不受谐波和直流分量影响,计算精度高。借助有效值的概念和抛物线插值方法实现反时限过激磁保护功能,该方法能较好地拟合发电机、变压器过激磁的曲线,满足工程设计要求。

The RMS value of excitation-voltage is figured out with sampling values of three-phase line voltages and simulative results show that it has high precision,being independent of system frequency. The real part or imaginary part of the voltage measurement calculated with Fourier transform is used as the input of the linear interpolation method and two zero-crossing points adjacent to it are used to calculate system frequency and period. Simulative results show that,the proposed algorithm is immune to harmonics and DC component with high precision. The equivalent RMS concept and parabolic interpolation method are applied to realize the function of inverse time-lag over-excitation protection,which fits better the over- excitation curve of generator or transformer and meets the requirements of engineering design.