Distance protection for transmission lines

Distance protection for transmission lines – SIPROTEC 7SA522


The SIPROTEC 7SA522 relay provides full-scheme distance protection and incorporates all functions usually required for the protection of a power line. The relay is designed to provide fast and selective fault clearance on transmission and subtransmission cables and overhead lines with or without series capacitor compensation. The power system star point can be solid or resistance grounded (earthed), resonant-earthed via Peterson coil or isolated. The SIPROTEC 7SA522 is suitable for single-pole and three-pole tripping applications with and without tele (pilot) protection schemes.

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Features & functions

Distance protection for transmission lines SIPROTEC 7SA522


The SIPROTEC 7SA522 incorporates several protective functions usually required for transmission line protection.

  • High-speed tripping time
  • Suitable for cables and overhead lines with or without series capacitor compensation
  • Self-setting power swing detection for power swing frequencies up to 7 Hz

Digital relay-to-relay communication for two and three terminal topologies

  • Adaptive auto-reclosure (ADT)


  • Binary inputs: 8 to 24

  • Binary outputs : 16 to 44
  • High-speed trip outputs: 5/10 (optional)
  • Text display
  • Surface-mounting or flush-mounting housing

Communication interfaces

  • System port 
    – IEC 61850

    – IEC 60870-5-103 
    – DNP 3 

  • Service port
    – DIGSI 4
    – Modem
  • 2 serial protection data interface for teleprotection
  • Front port
    – DIGSI 4
  • Time synchronization via IRIG B, DCF 77 or system interface


Protection functions

  • Non-switched distance protection with 6 measuring systems (21/21N)

  • High resistance ground (earth)-fault protection for single and three-phase tripping (50N, 51N, 67N)

  • Tele (pilot) protection (85)

  • Fault locator (FL)

  • Power swing detection / tripping (68/68T)

  • Phase-overcurrent protection (50/51)

  • STUB bus overcurrent protection (50STUB)

  • Switch-onto-fault protection (50HS)

  • Over/undervoltage protection (59/27)

  • Over/underfrequency protection (81O/U)

  • Auto-reclosure (79)

  • Synchro-check (25)

  • Breaker failure protection (50BF)

Control functions

  • Commands for control of CB and isolators

Monitoring functions

  • Trip circuit supervision (74TC)

  • Self-supervision of the relay

  • Measured-value supervision

  • Event logging/fault logging

  • Oscillographic fault recording

  • Switching statistics

Front design

  • User-friendly local operation with numeric keys

  • LEDs for local alarm

  • PC front port for convenient relay setting

  • Function keys


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