Transformer differential protection

Transformer differential protection – SIPROTEC 7UT63

SIPROTEC 7UT63 (phase-out product)

The SIPROTEC 7UT63 and 7UT635 differential protection relays 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. The specific application can be chosen by parameterization. In this way an optimal adaptation of the relay to the protected object can be achieved.

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Features & functions

Transformer differential protection SIPROTEC 7UT63 (phase-out product)


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 ground-fault protection, a negative-sequence protection and a breaker failure protection can be used. 7UT633 features 4 voltage inputs. With this option an overvoltage and undervoltage protection is available as well as frequency protection, reverse / forward power protection, fuse failure monitor and overexcitation protection. 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.


7UT63x features full coverage of applications without external relays by the option of multiple protection functions e.g. overcurrent protection is available for each winding or measurement location of a transformer. Other functions are available twice: ground-fault differential protection, breaker failure protection and overload protection. Furthermore, up to 12 user-defined (flexible) protection functions may be activated by the customer with the choice of measured voltages, currents, power and frequency as input variables. 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-defi ned messages can be generated as well. The flexible communication interfaces are open for modem communication architectures with control system.



  • 12/16 current transformers, 1/2 IEE
  • 4/0 voltage transformers
  • 21/29 binary inputs
  • 24 binary outputs
  • Graphic display
  • Surface-mounting or flush-mounting housing

Communication interfaces

  • System port 
    – IEC 61850

    – IEC 60870-5-103 

    – DNP 3.0


  • 2 service ports

    – DIGSI 4

    – Modem

    – Thermobox

  • Front port

    – DIGSI 4

  • Time synchronization via IRIG B, DCF77 or system interface


Function overview

  • Differential protection for 2- up to 3-winding transformers up to 5 ends (3-/1-phase)

  • Differential protection for motors and generators

  • Differential protection for short 2 up to 5 terminal lines

  • Differential protection for busbars up to 12 feeders (phase-segregated or with summation CT)

Protection functions

  • Differential protection with phase-segregated measurement

  • Sensitive measuring for low-fault currents

  • Fast tripping for high-fault currents

  • Restraint against inrush of transformer

  • Phase /ground overcurrent protection

  • Overload protection with or without temperature measurement

  • Negative-sequence protection

  • Breaker failure protection

  • Low/high-impedance restricted ground fault (REF)

  • Voltage protection functions

Control functions

  • Commands for control of circuit-breakers and isolators

  • 7UT63x: Graphic display shows position of switching elements, local/remote switching by key-operated switch

  • 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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