Parameterization of a Coordinated Protection Scheme for a 400/110 kV Power Transformer using a Multifunction Digital Relay SEL-787

Authors

  • Vladimir Szomosi Technical University of Košice, Department of Electric Power Engineering
  • Patrik Šoltés Technical University of Košice, Department of Electric Power Engineering
  • Emilia Chira Department of Electrical Engineering, Electronic and Computer Technical University of Cluj Napoca
  • Daniel Danci Department of Electrical Engineering, Electronic and Computer Technical University of Cluj Napoca
  • Cristian Barz Department of Electrical Engineering, Electronic and Computer Technical University of Cluj Napoca
  • Olivian Chiver Department of Electrical Engineering, Electronic and Computer Technical University of Cluj Napoca

Abstract

This paper presents a comprehensive methodology for the parameterization of a protection scheme for a critical 250 MVA, 400/110 kV power transformer, a vital asset in electrical substations. The protection is implemented using a modern Schweitzer Engineering Laboratories (SEL) SEL-787 multifunction digital relay. The critical importance of robust power transformer protection is underscored, as failures can lead to significant grid instability and economic loss. This work details the analytical process for setting key protection functions, including the primary percentage-restrained differential protection (ANSI 87) and the backup time-independent overcurrent protection (ANSI 50). Furthermore, the parameterization of essential ancillary functions such as thermal overload (ANSI 49), frequency (ANSI 81), and undervoltage (ANSI 27) is addressed. A complete, coordinated set of calculations and final settings is presented, derived from detailed system parameters and aligned with the principles outlined in relevant IEC and IEEE standards. The study serves as a practical case study, demonstrating the application of modern protection philosophy to ensure both the dependability and security of high-voltage power transformers.

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Published

2025-11-03

Issue

Vol. 18 No. 2 (2025)

Section

Power Systems Relaying, Faults Analysis

License

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