Impacts of the Sampling Rate on Responses of Digital Protective Relays

Digital protective relays are widely used in power systems, including industrial and commercial power systems. These modern protective devices have demonstrated several performance advantages over electromagnetic ones in terms of accuracy, reliability, and response speed. Performance advantages of digital protective relays are always dependent on the resolution of data used as their inputs, along with algorithms for fault detection and identification. This paper tests the performance of time-based, frequency-based, and time-frequency-based digital protective relays for various sampling rates. Tested sampling rates include low, medium, and high sampling rates (ranging from 16 to 256 samples/cycle). In this paper, the three types of digital protective relays are tested when deployed as the digital 87T transformer digital protection. Performance testing of these digital protective relays is carried out in terms of the accuracy and response speed. Test results show that low sampling rates adversely impact the accuracy and response speed of time-based, frequency-based, and time-frequency-based digital protective relays. Obtained results also reveal that medium and high sampling rates help improve the accuracy and response speed of digital protective relays.