Merging unit

Merging unit – SIPROTEC 6MU85


The SIPROTEC 6MU85 Merging Unit is the modular, interoperable and powerful solution between primary and secondary technology - versatile process data acquisition, autonomous automation and secure communication. It is designed for conventional and non-conventional instrument transformers (LPITs) and digitalizes all primary data close to the process.

IEC 61850 Edition 2.1. server certification

First IEC 61850 Edition 2.1 certificates worldwide for SIPROTEC 5 and SIPROTEC 7SX800

Siemens continues not only to drive standards and conformance procedures, but also to deliver the matching products. The relays passed the conformity tests including conformity to the process bus product standard IEC 61869-9. The process bus conformity involves both the Publishing and Subscribing of SampledValues.

Merging unit SIPROTEC 6MU85

Features & functions

SIPROTEC 5 process bus provides versatile solutions and migration concepts for new and existing systems.


The SIPROTEC 6MU85 merging unit has many faces and, just like all SIPROTEC 5 devices, adapts to your local situation and your individual applications. But no matter what your personal SIPROTEC merging unit looks like, at the process level, it is always the central data node with automation. Because, for the process bus, the SIPROTEC 6MU85 merging unit is the interoperable solution between primary equipment and secondary equipment. We show it to you using the example of a 3-winding transformer.

Benefits of SIPROTEC 5 merging unit

  • Modular functionality of protection, automation and control
  • Modular hardware
  • IEC 61850 Ed 2.1 compliant
  • SMV streams IEC 61869-9, IEC 61850-9-2 and IEC 61850-9-2 LE
  • Scada communication such as IEC 61850-8-1, IEC 60870-5-104, Modbus IP, Profinet IO S2, DNP3, PMU
  • Virtual and physical network segregation
  • Sample and time synchronization: IEEE 1588v2/PTP with enhanced stability against GNSS loss
  • Ruggedized design and conformal coated electronical boards for high electric strength and installations in harsh environments - as standard
  • Embedded cybersecurity


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 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)


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
  • PQ-Basic: voltage unbalance; voltage changes: overvoltage, dip, interruption; TDD, THD and Harmonics


  • Pluggable communication modules, usable for different and redundant protocols (IEC 61850-8-1, IEC 61850-9-2 Merging Unit, IEC 60870-5-103, IEC 60870-5-104, Modbus TCP, DNP3 serial and TCP, PROFINET IO, PROFINET IO S2 redundancy)
  • 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 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 data via a standard Web browser to display all information and diagnostic data, as well as vector diagrams, single-line and device display pages
  • Virtual network sharing (IEEE 802.1Q - VLAN)




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

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