Shahid Beheshti University International Journal of Research and Technology in Electrical Industry 2821-0190 2 2 2023 09 19 Restricted Earth Fault Protection Maloperation in Power Transformers and Optimal Settings to Improve its Performance 190 195 103637 10.48308/ijrtei.2023.103637 EN Reza Talebi Department of Electrical Engineering, Bu-Ali Sina University, Hamadan, Iran 0009-0008-0158-1050 Mohammad Hassan Moradi Department of Electrical Engineering, Bu-Ali Sina University, Hamadan, Iran 0000-0003-1498-0831 Journal Article 2023 04 24 <span lang="EN-GB" style="font-weight: normal;">Power transformers are one of the main components of the power grids. Several main and back up protection relays are provided to protect them against different fault types. Restricted Earth Fault (REF) protection relay is used as main protection to protect transformer against in-zone phase-to-ground faults. This protection has high accuracy to detect earth faults inside the transformer protection zone. Operational experiences show that in some cases and during external high current out-zone faults which leads to current transformers (CTs) core saturation, REF relay operates incorrectly and cause unwanted trip. Relay setting base and operation curve methods to solve the problem have been devised, but the problem has not yet been completely solved. In this article, different fault types such as symmetric/asymmetric, single/multiple phases, low/high current are simulated. Then, causes of REF protection maloperation and commercial relays settings and curves are studied. The optimal setting for the relay is extracted and its effectiveness</span> <span lang="EN-GB" style="font-weight: normal;">in different fault types validated by simulating real data with PSCAD and MATLAB software.</span> https://ijrtei.sbu.ac.ir/article_103637_9328283bf09fb59d03ebc615dff13a14.pdf