A smart resampling scheme for digital substation relay protection

The application of IEC61850 and non-conventional instrument transformers (NCIT) brings a new era in the development of substation. The protection intelligent electronic device (IED) in digital substation receives sampled data from different digital data sources (DDS) with digital interface based on IEC 61850-9-2 process bus. The mismatch in sampling rate between protection IED algorithms and different DDSs requires resampling in the protection IED to make sure the protection and other algorithms can run correctly. In this paper, a smart digital resampling scheme based on oversampling interpolator and quasi-continuous interpolator for fully digital relay protection is proposed. A computationally optimal poly-phase implementation structure and nyquist filter for the oversampling interpolator is designed and the Lagrange interpolation algorithm is chosen to approximate the impulse response of the quasi-continuous interpolator considering the reduction in error. Simulation results based on ATP/EMTD and MATLAB demonstrated the effectiveness of the proposed approach.