Merging unit

Merging unit – SIPROTEC 6MU85


The new SIPROTEC 6MU85 merging unit bases on the flexible SIPROTEC 5 system has been designed for conventional and non-conventional instrument transformers (LPITs) and digitalizes all primary data close to the process. SIPROTEC 5 process bus provides versatile solutions and migration concepts for new and existing systems.

Features & functions

Merging unit SIPROTEC 6MU85


Main functions:

  • Merging unit
  • Bay unit for distributes busbur protection SIPROTEC 7SS85
  • Breaker functions
  • Backup protection functions
  • Additional functions


  • Up to 4 sampled measured value streams according IEC 61850-9-2 LE or IEC 61869 flexible streams

Hardware flexibility:

  • Flexibly adjustable and expandable I/O quantity structure within the scope of the modular SIPROTEC 5 system; 1/6 expansion modules can be added.

Housing width:

  • 1/3 × 19 inches to 2/1 × 19 inches

As standard:


Merging unit

  • Per ETH-BD-2FO Ethernet module 1 or 2 (in preparation) Sampled Measured Value (SMV) streams 
  • - up to 32 analog values in any combination of CTs and VTs
    - 4x CTs, 4x VTs (IEC 61850-9-2 LE)
  • Up to 4 ETH-BD-2FO modules possible
  • Reliable and redundant data transmission via PRP protocol
  • IEC 61869-9, IEC 61869-13 compliant
  • IEC 61850-8-1 GOOSE, MMS and merging unit protocol on the same Ethernet module
  • Sample and date/time synchronization via IEEE 1588v2/PTP
  • Redundant power supply
  • Extended temperature range (-40 ºC to 70 ºC)

Merging unit functionality is also available for all modular SIPROTEC 5 protection devices.


Breaker functions

  • Control with switchgear interlocking
  • Circuit-breaker failure protection (50BF)
  • Circuit-breaker wear monitoring
  • Switching statistics
  • Point on wave switching (PoW)
  • Trip-circuit supervision (74TC)
  • Automatic reclosing (79)
  • Synchrocheck (25)

Backup protection functions

  • Non-directional overcurrent protection (50/51, 50N/51N)
  • Directional overcurrent protection (67/67N)
  • Overvoltage and undervoltage protection (27/59) 

Additional functions

  • Phasor measurement unit (PMU) for synchrophasor measured values and IEEE C37.118 protocol
  • Arc protection
  • Auxiliary functions for simple tests and commissioning
  • Temperature measurement via thermobox TR1200 (7XV5662-6AD10 or 7XV5662-8AD10)
  • 4-20 mA transducer inputs for various analog process values, e.g pressure, tap-changer position


  • Pluggable communication modules, usable for different and redundant protocols (IEC 61850-8-1, IEC 61850-9-2, IEC 60870-5-103, IEC 60870-5-104, Modbus TCP, DNP3 serial and TCP, PROFINET IO)
  • Serial protection data communication via optical fibers, two-wire connections and communication networks (IEEE C37.94, and others), including automatic switchover between ring and chain topology
  • Extensive cyber security functionality, such as role-based access control (RBAC), protocolling security-related events or signed firmware
  • Simple, quick and secure access to device data via a standard Web browser – without additional software



Merging unit for

  • Analog and digital feeder values
  • One central merging unit or distributed merging unit for the process data acquisition of a transformer protection schema
  • Central protection
  • Bay unit for distributed busbar protection
  • Fault recorder for process bus
  • Centralized synchrocheck

Merging unit functionality can also be added to all modular SIPROTEC 5 protection devices.


  • Adaptable to multiple CT, VT, LPIT inputs
  • Scalable number of binary inputs and outputs
  • Expandable by a 2nd row
  • Direct “high speed” tripping of circuit breaker < 1 ms
  • Collection of additional data (temperature, pressure, tap changer positions, …)
  • Cyber security in accordance with NERC CIP and BDEW Whitepaper requirements
  • Highest availability even under extreme environmental conditions  by “conformal coating“ of electronic boards
  • Merging unit functionality can also be added to all modular SIPROTEC 5 protection devices