M-3311 Transformer Protection System

Please Note: As of 12/31/2022, Beckwith Electric will no longer be manufacturing the M-3311 Transformer Protection System.

  • Beckwith will accept orders for these products until 8/31/2022 and all products ordered must ship before 12/31/2022.
  • Please contact us to request a quote and place orders.
  • This product may have an alternative replacement product, M-3311A, depending on your application needs. Please contact us for details.


  • For Transformers of All Sizes:
    • 2 or 3 winding Transformers
    • Unit Wrapping of Generating Plants
    • Unit Protection of Other Electrical Apparatus and certain Bus Arrangements (including those with a transformer in the zone)
  • Additional Applications: System Backup Protection, Load Shedding (voltage and frequency), Bus Protection, and individual Breaker Failure Protection for each winding input

Standard Protective Functions

  • Negative-sequence inverse time overcurrent (46)
  • Winding thermal protection (49)
  • Three winding instantaneous phase overcurrent (50)
  • Breaker Failure (50BF)
  • Instantaneous ground overcurrent (50G)
  • Instantaneous residual overcurrent (50N)
  • Three winding inverse time phase overcurrent (51)
  • Inverse time ground overcurrent (51G)
  • Inverse time residual overcurrent (51N)
  • Three winding, phase differential (87T) and High Set instantaneous (87H)
  • Ground differential (87GD)
  • Six External input functions with individual timers

Optional Single‑Phase Voltage Protection Package

  • Overexcitation (24) V/Hz, two definite time and one inverse time elements
  • Phase undervoltage (27) function for load shedding
  • Ground Overvoltage (59G)
  • Over/Underfrequency (81O/U)

Standard Features

  • Four Setpoint Groups
  • Eight programmable outputs and six programmable inputs
  • Oscillographic recording
  • 32-target storage
  • Real time metering of measured and calculated parameters, including demand currents
  • Two RS-232 and one RS-485 communications ports
  • Standard 19″ rack-mount design
  • Removable printed circuit board and power supply
  • 50 and 60 Hz models available
  • 1 or 5 A rated CT inputs available
  • M-3820B IPScom® Communications Software
  • IRIG-B time synchronization
  • Includes MODBUS, BECO 2200 and DNP 3.0 protocols

Optional Features

  • Redundant Power Supply
  • M-3911 Target Module
  • M-3931 Human-Machine Interface (HMI) Module
  • M-3801D IPSplot® PLUS Oscillograph Analysis Software