AQ-T256 Transformer protection device


AQ-T256 is a transformer protection device with sophisticated and easy-to-use differential protection functions. The relay provides overcurrent protection for both low-voltage and high-voltage sides, earth fault protection, negative sequence overcurrent protection as well as two independent instances of restricted earth fault protection. You can add up to ten (10) I/O or communication cards into the device for extensive monitoring and control applications. AQ-T256 is a transformer protection device with a sophisticated and easy-to-use differential protection function. communicates using various protocols, including the IEC 61850 substation communication standard.


  • A large I/O capacity.
  • Both predefined and customizable connection group selection.
  • 2nd and 5th harmonic blocking.
  • Automatic verification of connection group and nominal value settings.
  • Overloading and through fault statistics for preventive maintenance.

Technical data

  • Non-directional overcurrent (I>; 50/51) - 4 stages (INST, DT or IDMT)
  • Non-directional earth fault (I0>; 50N/51N) - 4 stages (INST, DT or IDMT)
  • Negative sequence overcurrent/ Phase current reversal/ Current unbalance (I2>; 46/46R/46L) - 4 stages (INST, DT or IDMT)
  • Harmonic overcurrent (Ih>; 50H/51H/68H) - 4 stages (INST, DT or IDMT)
  • Circuit breaker failure protection (CBFP; 50BF/52BF)
  • Resistance temperature detectors (RTD)
  • Transformer thermal overload (TT>; 49T)
  • Generator/transformer differential (Idx>; 87T/87M/87G)
  • Transformer status monitoring
  • Programmable stage (PGx>/<; 99)
  • Arc protection (IArc>/I0Arc>; 50Arc/50NArc) (optional)

  • Number of objects to control and monitor: 10
  • Number of indicators to monitor: 10
  • Number of setting groups: 8
  • Switch-on-to-fault

  • Phase, sequence and residual currents (IL1, IL2, IL3, I01, I02)
  • Current transformer supervision - 2 instances
  • Circuit breaker wear monitoring
  • Total harmonic distortion (current)
  • Measurement recorder
  • Measurement value recorder
  • Event recorder (max. 15 000 permanent event records)
  • Disturbance recorder (max. 100 records á 5 seconds at 3.2 kHz sampling)

  • Current inputs: 10
  • Digital inputs (fixed): 3
  • Digital outputs (fixed): 5
  • Number of empty slots: 10
  • Digital inputs: +8/16/24/32/40/48/56/64/72/80 (optional)
  • Digital outputs: +5/10/15/20/25/30 (optional)
  • Milliampere I/O module (4 mA outputs + 1 mA input)
  • Arc protection module (4 sensors + 2 HSO + 1 BI)
  • Communication media (see "Communication" below)
  • External I/O modules (see "Accessories" below)

  • Communication inputs
  • RJ-45 100 Mbps Ethernet (front panel, fixed)
  • RJ-45 100 Mbps Ethernet and RS-485 (rear panel, fixed)
  • 2 x RJ-45 100 Mbps Ethernet with an IRIG-B input (optional)
  • 2 x ST 100 Mbps Ethernet with an IRIG-B input (optional)
  • 2 x LC 100 Mbps Ethernet (PRP/HSR) (optional)
  • RS-232 serial fiber (PP/PG/GP/GG) (optional)
  • Communication protocols
  • IEC 61850 (edition 1)
  • IEC 61850 (edition 2)
  • IEC 60870-5-101/104
  • IEC 60870-5-103
  • Modbus/RTU and Modbus/TCP
  • DNP3
  • SPA

  • AX007 External 6-channel 2-/3-wire RTD input module (pre-configured)
  • AX008 External 8-channel thermocouple and mA input module (pre-configured)
  • AX013 Raising frame (120 mm)
  • AX014 Raising frame (40 mm)
  • AX015 Wall mounting bracket

Additional material

Application Drawing

An application image for AQ-T256A transformer protection device, with one version drawn according to IEC standard symbols and the other according to IEEE/ANSI standard symbols.

Device Rear Image

Device rear image_AQ-256-AAAAAAAAAA

Device and Cut-out Image

AQ-250 dimensions and cut-out

Order Code

Order code_T256A

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