Comparison of Programmable Logic and Setting Group Methods for adaptive overcurrent protection in microgrids

Adaptive overcurrent protection systems for microgrids with distributed generators require that overcurrent relays need to be adjusted to different circuit paths and feeder fuses. Adaptive overcurrent protection systems in recent publications were based on the Setting Group method, using the functions resident in the relay. In this paper, the Programmable Logic method was developed for an adaptive overcurrent protection system, using the programmable logic and math operators instead of the functions resident in the relay. The Programmable Logic and Setting Group methods were validated using a real-time simulator with two relays in-the-loop. The selectivity, reliability and speed of the adaptive protection system based on the Programmable Logic and Setting Group (previous work) methods were compared for a microgrid with distributed generators (diesel generators). Similar results were obtained with both methods. However, the Setting Group method limited the number of overcurrent settings by the available setting groups of relays, and disabled the relays for a fixed amount of time, reducing the relay's availability. On the other side, the Programmable Logic method is recommended because it improves the capacity of relays by using one setting group, and avoids relays to be disabled because switching setting groups is not being necessary. In microgrids that require an adaptive overcurrent protection system for different circuit paths and seasonal (winter and summer) settings, adaptive overcurrent protections based on programming alternative is a better solution. This requires relay engineers to be trained in relays’ programming techniques.