母线保护中电流互感器的深度饱和辅助判据

Distinguish current transformer's extreme saturation by waveform discrimination of branch current

通过比较电流互感器未饱和及深度饱和时二次电流波形特点,分析了通过谐波比确定电流互感器饱和的不足之处,提出一种新的波形鉴别判据,作为谐波制动的辅助判据。该方法是将采样波形取绝对值,定义数据窗长度为半个周期。在每个数据窗内找到一个极大值Ymax,设假想门槛Yα,使Yα=kYmax。用数据窗内每个采样点的值与假想门槛作比较,当采样点大于假想门槛,则计数器加1。仿真与动模实验的结果表明了辅助判据的可行性,从而解决了单纯依靠差流波形的谐波比来确定电流互感器饱和,在电流互感器发生深度饱和时可能出现的误开放问题。

The secondary current waves of unsaturated and extremely saturated current transformers are compared to show the insufficiency of saturation discrimination by harmonic ratio. A waveform discrimination criterion is brought forward to assist harmonic braking. It changes the sampling waves into absolute values and set half period as data window length. An imaginary threshold（Yα） is set to k times of the extreme value in each data window（Ymax） and compared with each sampling data. When the sampling data is bigger than the imaginary threshold,the counter will plus one. Its feasibility is validated by simulation and physic experiment,which avoids the misoperation during current transformer extreme saturation when only judged by harmonic ratio of differential waveform.