Restricted Earth Fault Protection Maloperation in Power Transformers and Optimal Settings to Improve its Performance

Document Type : Research Article

Authors

Department of Electrical Engineering, Bu-Ali Sina University, Hamadan, Iran

Abstract

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 in different fault types validated by simulating real data with PSCAD and MATLAB software.

Keywords

Main Subjects

Research and Technology in the Electrical Industry
Volume 1, Issue 2
September 2022
Pages 194-199

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History

  • Receive Date: 24 April 2023
  • Revise Date: 18 June 2023
  • Accept Date: 29 June 2023

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