Protective Algorithm under Conditions of Sampling Data Lost in Communication in Smart Substation

In smart substation, sampling data will be lost when data frame has been lost or destroyed in transmission progress, which will result in protective action delay or blocked when fault occurs. For this reason, this paper suggests to find the lost sampling data's fitted value and use them to replace the lost sampling data in protective calculation to ensure protection act fast and accurately based on correlative protective algorithm to clear or isolate the fault from power system in such condition, which is good for power system's safe and steady operation in the end. Two methods to obtain the fitted value of lost sampling data are proposed in the paper, one is based on cubic spline interpolation method, which can be used in any voltage grade power system, the other is curve fitting interpolation method based on mathematical model, and can only be used in low-voltage grade power system because of high harmonics are not taken into account in the method. The two methods have been correctly proved by simulation of MATLAB and RTDS, and they can meet requirements of engineering. One type of EHV line protective device has been made based on theory above and some devices have been put into normal operation on site.