Digital Differential Protection for 3 phi Solid-State Transformers


Saleh S. A. , ÖZKOP E.

IEEE TRANSACTIONS ON INDUSTRY APPLICATIONS, vol.57, no.4, pp.3474-3486, 2021 (Journal Indexed in SCI) identifier identifier

  • Publication Type: Article / Article
  • Volume: 57 Issue: 4
  • Publication Date: 2021
  • Doi Number: 10.1109/tia.2021.3072877
  • Title of Journal : IEEE TRANSACTIONS ON INDUSTRY APPLICATIONS
  • Page Numbers: pp.3474-3486
  • Keywords: ANSI 87 T protection function, differential protection, digital filters, digital protection, dq0-axis components, three-phase solid-state transformers, MODULAR PROTECTION, SYSTEMS, PERFORMANCE

Abstract

This article presents the development, implementation, and testing of a digital differential protection for three-phase (3 phi) solid-state transformers (SSTs). The developed digital differential protection is designed to implement the ANSI 87 T protection function. The differential currents used by the developed protection are created by the dq0 components of the currents flowing in the high and low voltage sides of a 3 phi SST. Internal faults are detected and identified using the energy contents of high-frequency subbands present in the dq0 differential currents. The desired high-frequency subbands are extracted using the phaselet transform that processes signals without sensitivity to nonstationary changes in their frequency and/or phases. Energy contents in the extracted high-frequency subbands allow accurate, fast, and reliable detection and identification of faults in any part of a 3 phi SST. The proposed digital differential protection is implemented for performance testing using a laboratory 25-kVA 3 phi SST. Performance results demonstrate accurate, fast, and reliable response to different fault and nonfault events. Furthermore, responses of the developed differential protection are found to be consistent regardless of the fault type, fault location, and/or loading level.