Design and implementation of a multifunction DSP-based-numerical relay

•Protection against over-current, over/under-voltage and over/under-frequency.•The relay serves also as a directional relay.•The relay gives a definite time delay before the load shedding.•The relay avoids mal-function operation during transient conditions.

This paper is aimed at proposing a multifunction numerical relay (MNR) for protection against over-current, over- and under-voltage and over- and under-frequency. The MNR serves also as a directional relay. The performance of the MNR is investigated through simulation using MATLAB/Simulink and implementation of a prototype using TMS320F28335 Experimenter Kit. The MNR trips a circuit breaker at abnormal conditions of current, voltage and frequency. The novelty of the proposed relay lies on being a numerical compact-sized relay serving multi protection functions.