Transformer differential protection

Transformer differential protection – SIPROTEC 7UT612

SIPROTEC 7UT612 (phase-out product)

The SIPROTEC 7UT612 differential protection relay are used for fast and selective fault clearing of short-circuits in transformers of all voltage levels and also in rotating electric machines like motors and generators, for short lines and busbars. The protection relay can be parameterized for use with threephase and single-phase transformers.

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Features & functions

Transformer differential protection SIPROTEC 7UT612


The specific application can be chosen by parameterization. In this way an optimal adaption of the relay to the protected object can be achieved.


In addition to the differential function a backup overcurrent protection for 1 winding / star point is integrated in the relay. Optionally, a low or high-impedance restricted earth-fault protection, a negative sequence protection and a breaker failure protection can be used. With external temperature monitoring boxes (thermo-boxes) temperatures can be measured and monitored in the relay. Therefore, complete thermal monitoring of a transformer is possible, e.g. hot-spot calculation of the oil temperature. The relays provide easy-to-use local control and automation functions. The integrated programmable logic (CFC) allows the users to implement their own functions, e.g. for the automation of switchgear (interlocking). User-defined messages can be generated as well. The flexible communication interfaces are open for modem communication architectures with control system.


The protection relay can be parameterized for use with three-phase and single-phase transformers. In addition to this, a thermal replica is integrated for the supervision of the ohmic losses in the plant.



  • 7 current transformers, 1 IEE

  • 3 binary inputs

  • 4 binary outputs

  • Text display
  • Surface-mounting or flush-mounting housing

Communication interfaces

  • System port 
    – IEC 61850

    – IEC 60870-5-103 

    – DNP 3.0


  • Service port

    – DIGSI 4

    – Modem

    – Thermobox

  • Front port

    – DIGSI 4

  • Time synchronization via IRIG B, DCF77 or system interface


Function overview

  • Differential protection for two-winding transformers (3-/1-phase)

  • Differential protection for motors and generators

  • Differential protection for short lines

  • Differential protection for busbars up to 7 feeders (phase-segregated or with summation CT)

Protection functions

  • Differential protection with phase-segregated measurement

  • Sensitive measuring stage for low-fault currents

  • Fast tripping for high-fault currents

  • Restraint against inrush of the transformer

  • Phase/ground-overcurrent protection

  • Overload protection with or without temperature measurement

  • Negative-sequence protection

  • Breaker failure protection

  • Low-or high-impedance restricted earth fault (REF)

Control functions

  • Commands for control of c.b. and isolators

  • Control via keyboard, binary inputs, DIGSI 4 or SCADA system

  • User-defined logic with CFC

Monitoring functions

  • Self-supervision of the relay

  • Trip circuit supervision

  • Oscillographic fault recording

  • Permanent differential and restraint current measurement, extensive scope of operational values


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