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Different technologies have been used for more than one hundred years for designing and manufacturing protective relays. Many techniques previously used in electromechanical and solid-state relays are now used in numerical relays. An appreciation of the previous technologies is important for knowing the roots of protection and avoiding the phenomenon of re-inventing the wheel. The development of electromagnetic, electromechanical, solid-state, and numerical technologies is reviewed in Section 2 of this report. Modern numerical relays perform many functions other than protection. Some of the more commonly performed functions are identified in this section as well.


The third section addresses the issues concerning the protection of transformers.

The fourth section is devoted to monitoring transformers.

Control of transformers is addressed in the fifth section of this report.

Section six provides a brief description of techniques used in numerical relays for processing sampled and quantized data. While a very large number of techniques are reported in the literature, many techniques that are presently being used or have the potential of being used in numerical relays are described.

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20 WhatsApp Groups for protection engineers to join:

  • WhatsApp Grp 01: Protection Relay – General
  • WhatsApp Grp 02: Substation Automation – General
  • WhatsApp Grp 03: Transmission line protection
  • WhatsApp Grp 04: Transformer protection
  • WhatsApp Grp 05: Motor protection
  • WhatsApp Grp 06: Generator protection
  • WhatsApp Grp 07: Overcurrent and Earth Fault Protection
  • WhatsApp Grp 08: Busbar protection and Bay controller
  • WhatsApp Grp 09: Breaker protection and control
  • WhatsApp Grp 10: Protection Relay Testing and commissioning
  • WhatsApp Grp 11: DIgSILENT
  • WhatsApp Grp 12: ETAP
  • WhatsApp Grp 13: PSCAD
  • WhatsApp Grp 14: IEC 61850 configuration
  • WhatsApp Grp 15: Switchgear GIS & AIS
  • WhatsApp Grp 16: GE Relay Configuration
  • WhatsApp Grp 17: SIEMENS Relay configuration
  • WhatsApp Grp 18: Schnider Relay configuration
  • WhatsApp Grp 19: SEL Relay Configuration
  • WhatsApp Grp 20: ABB Relion configuration

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