Overcurrent and feeder protection

Overcurrent and feeder protection – SIPROTEC 7SJ81


The SIPROTEC 7SJ81 overcurrent protection has specifically been designed for a cost-effective and compact protection of feeders and lines in medium-voltage systems. 

Overcurrent and feeder protection SIPROTEC 7SJ81

Features & functions

With its flexibility and the powerful DIGSI 5 engineering tool, the SIPROTEC 5-device offers future-oriented solutions for protection, control, automation, monitoring and PQ basic.


Main function:

  • Feeder and overcurrent protection 

Inputs and outputs:

  • 4 current transformers, 11 binary inputs, 9 binary outputs
  • 4 current transformers, 18 binary inputs, 14 binary outputs
  • 4 current transformers, 4 voltage transformers, 11 binary inputs, 9 binary outputs
  • 4 current transformers, 4 voltage transformers, 16 binary inputs, 11 binary outputs

Hardware flexibility:

  • Different hardware quantity structures for binary inputs and outputs are available in the 1/3 base module. 1 plug-in module position, available with large or small display

Housing width:

  • 1/3 × 19 inches

As standard:


DIGSI 5 permits all functions to be configured and combined as required.

  • Directional and non-directional overcurrent protection with additional functions
  • Detection of ground faults of any type in compensated or isolated electrical power systems using the following functions: 3I0>, V0>, transient ground fault, cos φ, sin φ, dir. detection of intermittent ground faults, harmonic detection and admittance measurement
  • Detection of intermittent ground faults with automatic blocking of static measuring functions, to avoid message and fault record flooding
  • Arc protection (note the resulting communication restrictions)
  • Overvoltage and undervoltage protection
  • Frequency protection and frequency change protection for load shedding applications
  • Power protection, configurable as active or reactive power protection
  • Directional reactive power undervoltage protection (QU protection)
  • Control with switchgear interlocking protection
  • Synchrocheck
  • Circuit-breaker failure protection
  • Detection of current and voltage signals up to the 50th harmonic with high accuracy for selected protection functions and operational measured values
  • PQ-Basic: voltage unbalance; voltage changes: overvoltage, dip, interruption; TDD, THD and Harmonics
  • Graphical logic editor to create powerful automation functions in the device
  • Single-line representation in small or large display
  • Integrated electrical Ethernet RJ45 for DIGSI 5 and IEC 61850 (reporting and GOOSE)
  • 1 optional, plug-in module for a) communication protocols or b) for arc protection
  • Redundant and simple communication protocols according to IEC 61850-8-1, IEC 60870-5-103, IEC 60870-5-104, Modbus TCP, DNP3 serial and TCP, PROFINET IO
  • Reliable data transmission via PRP and HSR redundancy protocols
  • Extensive cybersecurity functionality, such as role-based access control (RBAC), protocolling security-related events, signed firmware or authenticated network access IEEE 802.1X
  • Simple, quick and secure access to the device via a standard Web browser to display all information and diagnostic data, as well as vector diagrams, single-line and device display pages
  • Time synchronization using IEEE 1588
  • Standard fault recording (buffer for a max. record time of approx. 40 sec. at 2 kHz)
  • Auxiliary functions for simple tests and commissioning



  • Detection and selective 3-pole tripping of short circuits in electrical equipment of star networks, lines with infeed at one or two ends, parallel lines and open-circuited or closed ring systems of all voltage levels
  • Detection of ground faults in isolated or arc-suppression-coilground power systems in star, ring, or meshed arrangement
  • Backup protection for differential protection devices of all kind for lines, transformers, generators, motors, and busbars
  • Universal line protection
  • Simple load shedding applications
  • Acquisition and recording of power quality data in the medium voltage and subordinate low voltage network


  • Compact and low-cost overcurrent protection
  • Safety due to powerful protection functions
  • Purposeful and easy handling of devices and software thanks to a user-friendly design
  • Cybersecurity according to NERC CIP and BDEW Whitepaper requirements (for example, logging security-related events and alarms)
  • Highest availability even under extreme environmental conditions by “conformal coating“ of electronic boards
  • Full compatibility between IEC 61850 Editions 1, 2.0 and 2.1

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