A research on multi digital source differential protection

In a digital substation, protection equipment may get data from different digital sources. This paper researched a form of multi digital sources. As link devices between primary side and secondary side, optical current transformers (OCT) may run on different sampling frequencies. Literatures have proposed that by the means of TCFIR [1], differential protection can get signals with the same sampling frequency in each branch. According to Nyquist Sampling Theorem, anti-aliasing filters set in front of OCTs with different sampling frequencies would also have different cut-off frequency. An effective method is presented in this paper. Different current error caused by different filters can be reduced by doing frequency domain compensation on current signal according to filter´s frequency domain characteristics. These methods are confirmed by simulation in MATLAB.