Busbar protection

Busbar protection – SIPROTEC 7SS85


The SIPROTEC 7SS85 busbar protection is a selective, safe and fast protection against busbar short circuits in medium voltage systems, high voltage systems, and systems for very high voltage with a large variety of busbar configurations. The SIPROTEC 7SS85 can be used both as a centralized and a distributed solution. Selection of the device base functionalities (significant properties) and the modular hardware structure permit optimum adaptation of the SIPROTEC 7SS85 to a large variety of system configurations and functional requirements up to a comprehensive station protection.

Features & functions

Busbar protection SIPROTEC 7SS85


Selection of the device base functionalities (significant properties) and the modular hardware structure permit optimum adaptation of the SIPROTEC 7SS85 to a large variety of system configurations and functional requirements.



The busbar protection SIPROTEC 7SS85 encompasses the following maximum quantity structure:

  • 20 3-phase measuring points (current transformer)

  • 4 3-phase measuring points (voltage transformer)

  • 26 bays (feeders, couplers, bus-section disconnections)

  • 6 bus zones (busbar sections with measuring function)

  • 6 couplers (with 1 or 2 current transformers)

  • 3 auxiliary busbars (busbar sections without measuring function)

  • Phase-selective measurement and Display

  • Selective tripping of faulty busbar sections

  • Optional additional decentralized binary in- and outputs via protection interface (PI) or IEC 61850 (GOOSE) provide new concepts for busbar protection

As standard:


All functions can be configured as required with DIGSI 5. Using some functions requires the appropriate number of free function points to be available in the device. The function point calculator in the online configurator provides support in the determination of the required number of function points for your device. The necessary function points are also shown during project engineering with DIGSI 5.


Characteristic Key Values of SIPROTEC 7SS85

  • Phase-selective measurement and display

  • Selective tripping of faulty bus zones

  • Disconnector-independent check zone as additional tripping criterion

  • Shortest tripping times (centralized busbar protection <7 ms; distributed busbar protection < 12 ms) to ensure network stability and minimize damage to the system

  • Highest stability in case of external faults, even in case of transformer saturation, through stabilization
    with flowing currents

  • Operate curve with freely adjustable characteristic curve sections

  • Additional operate curve with increased sensitivity for low-current errors, for example in resistance-grounded 
    power systems

  • Fast recognition of internal and external errors requires only 2 ms of saturation-free time of the current transformer

  • Using closed iron core or linearized current transformers in a plant is possible

  • Adaptation of different current transformer ratios per parameterization

  • Straight-forward dimensioning of current transformers and stabilization factor

  • Three interacting methods of measurement allow minimum tripping times after busbar faults and ensure maximum 
    stability in case of large short-circuit currents

  • The integrated circuit-breaker failure protection recognizes circuit breaker faults in the event of a busbar short 
    circuit and provides a trip signal for the circuit breaker at the line end. The adjacent busbar trips if a coupling circuit breaker fails

  • There is extensive monitoring of current transformer circuits, measured value acquisition and processing, and trip circuits. This prevents the protection from subfunction, which reduces the effort for routine checks.

  • Various control possibilities, such as bay out of order, acquisition blocking from disconnectors and circuit breakers, 
    blocking of protection zones or circuit-breaker failure protection, make the adaptation to operationally-caused special states of your plant easier

  • Optional 1/3-pole or 3-pole circuit-breaker failure protection using the integrated disconnector image for tripping 
    all circuit breakers of the busbar section affected

  • Optional end-fault protection for the protection of the section between circuit breaker and current transformer for feeders and bus couplers

  • Direct tripping of protection zones through external signals

  • Release of the tripping of a protection zone through additional external signals

  • Release of tripping through additional, external phase-selective signals

  • Optional phase/ground overcurrent protection for each bay

  • Optional voltage and frequency protection for up to two 3- phase voltage transformers. This may also be used for the 
    implementation of an integrated undervoltage release.

  • Optional cross stabilization as additional tripping release in 3- pole encapsulated gas-insulated switchgear.

  • Optional bus coupler differential protection for fault clearing in couplers with two current transformers.

  • 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

Function library and application templates

The flexibility of the SIPROTEC 7SS85 allows for the protection of a large number of possible system configurations. In place of application templates, DIGSI 5 makes a comfortable, fully graphical interface for complete engineering of your busbar protection available.


The SIPROTEC 7SS85 can be used both as central busbar protection and as the central unit of a distributed busbar protection solution. The SIPROTEC 7SS85 is suited for the following system configurations:

  • Single busbars with/without transfer busbar

  • Double busbars with/without transfer busbar

  • Triple busbars

  • Breaker-and-a-half layout method

  • Dual circuit-breaker systems and one or two current transformer(s) per feeder

  • Truck-Type Switchgear

  • Systems with combined busbars (alternatively main/transfer busbar)

  • T circuit arrangements

  • H connection arrangement with busbar coupler or disconnection

  • Ring busbars


Integrate your existing SIPROTEC 5 feeder protection devices as bay units of the distributed busbar protection SIPROTEC 7SS85 - based on IEC 61850-9-2 process bus.

Add SIPROTEC 5 merging units 6MU85 to new substation feeders and expand your SIPROTEC 7SS85 busbar protection system.

Benefits of distributed busbar process bus solution

  • Compatible with all relevant process bus standards such as IEC 61850-9-2 and IEC 61869-9
  • Sample and date/time synchronization via IEEE 1588v2/PTP
  • Existing SIPROTEC 5 feeder protection devices can be used as bay units
  • SIPROTEC 5 merging units digitalize the measured values directly at the process
  • Back-up protection functions integrated in the SIPROTEC 5 merging units offer additional system security
  • During commissioning all settings can be done with DIGSI 5 and the IEC 61850 system configurator directly via process bus network.
  • Interoperability with multivendor merging units (IEC 61850 Edition 2.1 compliance recommended)


  • Safety by measuring methods proven and reliable for 25 years.

  • Simple creation and adaptation of the configuration by the user over the entire service life

  • Clearly structured by fully graphical engineering and online plant visualization with DIGSI 5

  • Protection of up to 20 feeders with a single device

  • Safe and reliable automation and control of your systems

  • Cyber security in accordance with NERC CIP and BDEW Whitepaper requirements
  • Powerful communication components warrant safe and effective solutions
  • Highest availability even under extreme environmental conditions by “conformal coating“ (coating) of electronic boards