Generator protection

Generator protection – SIPROTEC 7UM85


The SIPROTEC 7UM85 generator protection device has been designed specifically for the protection of generators and power plant units. It contains all necessary main protection functions and a large number of other protection and monitoring functions. With its modular structure, flexibility and the powerful DIGSI 5 engineering tool, SIPROTEC 7UM85 offers future-oriented solutions for protection, control, automation, monitoring and PQ basic. For motors in explosive environments, the SIPROTEC 7UM85 is also available with EN 60079-14 or Verband der Elektrotechnik, Elektronik und Informationstechnik 0165, Part 1 (ATEX) certification.

Features & functions

Generator protection SIPROTEC 7UM85


Main function:

  • Typical generator protection functions
  • Certification for use in explosive environments (EN 60079-14 or Verband der Elektrotechnik, Elektronik und Informationstechnik 0165, Part 1, ATEX)
  • SIL2 certification of hardware and software for generator reverse protection EN 61508

Inputs and outputs:

5 predefined standard variants with

  • up to 16 current transformers and 
  • 8 voltage transformers, 
  • 7 to 15 binary inputs,
  • 9 to 20 binary outputs
  • 4 fast measuring transducer inputs (10 V or 20 mA)

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, available with large or small display, or without display

Width of housing:

  • 1/3 × 19 inches to 2 × 19 inches

As standard:


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

  • Short-circuit protection (overcurrent protection, impedance protection, differential protection)
  • Stator ground-fault protection (90% non-directional or directional, 100% with 3rd harmonic, real 100% protection with 20-Hz voltage interference)
  • Rotor ground-fault protection with different measuring methods (ground current or ground-resistance monitoring)
  • High-precision reverse-power protection and universal power protection
  • Underexcitation and overexcitation protection
  • Unbalanced-Load Protection
  • Overload protection and temperature supervision via external RTD unit (with PT 100, for example)
  • Out-of-Step  Protection
  • Rotor and stator overload protection with cold gas consideration (coolant temperature)
  • Power-plant disconnection protection
  • Shaft-current protection (in particular with hydropower applications)
  • Universal overvoltage and undervoltage protection with different measuring methods
  • Overfrequency and underfrequency protection, frequency change protection and monitoring of dwell time in frequency bands as turbine protection (protection against abnormal frequencies)
  • Protection functions for network decoupling (voltage and frequency protection, directional reactive power undervoltage protection (QU protection) and vector-jump protection)
  • Inadvertent energization protection to detect incorrect activation of the circuit breaker
  • Circuit-breaker failure protection
  • Point-on-wave switching
  • Circuit breaker reignition monitoring
  • Single-channel parallel connection function (synchronization) with adjustment commands for rotational speed (frequency) and voltage
  • Graphical logic editor to create powerful automation functions in the device
  • Integrated electrical Ethernet RJ45 for DIGSI 5 and IEC 61850 (reporting and GOOSE)
  • Up to 4 pluggable communication modules, usable for different and redundant protocols (IEC 61850-8-1, IEC 61850-9-2 Client, IEC 60870-5-103, IEC 60870-5-104, Modbus TCP, DNP3 serial and TCP, PROFINET IO, PROFINET IO S2 redundancy)
  • Virtual network sharing (IEEE 802.1Q - VLAN)
  • Reliable data transmission via PRP and HSR redundancy protocols
  • PQ-Basic: voltage unbalance; voltage changes: overvoltage, dip, interruption; TDD, THD and


  • 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
  • Phasor Measurement Unit (PMU) for synchrophasor measured values and IEEE C37.118 protocol
  • Time synchronization using IEEE 1588

  • Capturing operational measured variables and protection function measured values for the evaluation of the system, to support commissioning, and to analyze faults

  • Frequency tracked protection functions over a wide frequency range (10 Hz to 80 Hz) and the option to assign the protection functions in a single device to different frequency tracking groups.

  • Powerful fault recording (buffer for a max. record time of 80 sec. at 8 kHz or 320 sec. at 2 kHz)

  • Auxiliary functions for simple tests and commissioning

  • Flexibly adjustable I/O quantity structure within the scope of the SIPROTEC 5 modular system



  • Protection of generators in busbar connection of different power, with directional stator ground-fault protection.

  • Protection of generators in unit connection of different power (using the 100% stator ground fault (20 Hz) with larger generators)

  • Protection of power plant units with one device per protection group. In the generator transformer variant, the 7UM85
    implements both generator and transformer protection.

  • In more complex power plant units (unit connection with generator circuit breaker and several auxiliary transformers),
    additional SIPROTEC 5 devices are used, – for example, 7UT8x, 7SJ82 or 7SJ85 and 7SA, SD, SL86, at the upper-voltage side of the generator transformer.

  • Using motor and generator protection functions (underexcitation protection, for example) to protect synchronous motors.
  • Acquisition and recording of power quality data in the medium voltage and subordinate low voltage network.




  • Safe and reliable automation and control of your systems
  • Purposeful and easy handling of devices and software thanks to a user-friendly design
  • Cybersecurity in accordance with NERC CIP and BDEW Whitepaper requirements
  • Highest availability even under extreme environmental conditions by “conformal coating“ of electronic boards