Beckwith Electric's Transformer Protection System M-3311A provides protection, control, monitoring and user interface functions for two, three or four-winding transformers. The system includes restrained and unrestrained differential protection, overcurrent protection, and optional voltage, and underfrequency protection. Multiple setpoint groups and user-implementable logic schemes provide flexibility. Dual RS-232 ports and an RS-485 port provide user-interface capabilities.

Optional modules include the HMI module for front-panel operation and the target module to indicate trip target status and redundant power supply. The M-3311A can be purchased as a differential and overcurrent relay or with the Optional Voltage Protection Package. The M-3826 IPScom Communications Software is included for direct serial or remote communication access. Waveform data can be downloaded using IPScom® while the M-3801D IPSplot PLUS Oscillographic Analysis Software allows for plotting and printing of the downloaded oscillographic data.

  • Generator-Transformer Unit Overall Differential
  • 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
  • Options: Ethernet Connection and Expanded I/O

Standard Protective Functions

  • Negative-sequence inverse time overcurrent (46)
  • Winding thermal protection (49)
  • Four winding instantaneous phase overcurrent (50)
  • Breaker Failure (50BF)
  • Instantaneous ground overcurrent (50G)
  • Instantaneous residual overcurrent (50N)
  • Four winding inverse time phase overcurrent (51)
  • Inverse time ground overcurrent (51G)
  • Inverse time residual overcurrent (51N)
  • Two, three or four winding phase differential (87T) and high set instantaneous (87H)
  • Ground differential (87GD)
  • IPSlogicTM


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

  • Eight programmable outputs and six programmable inputs
  • Oscillographic recording
  • Through-Fault Monitoring
  • 10-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-3826 IPScom® Communications Software
  • IRIG-B time synchronization
  • Breaker Monitoring
  • Multiple Setpoint Groups
  • Trip Circuit Monitoring
  • Includes MODBUS and DNP 3.0 protocols
  • Summing Currents from mulitple sources for 49, 50, 51, 50N, 51N, 87 GD and Through Fault functions


Optional Features

  • Redundant Power Supply
  • M-3911A Target Module
  • M-3931 Human-Machine Interface (HMI) Module
  • M-3801D IPSplot® Plus Oscillograph Analysis Software
  • RJ45 Ethernet port utilizing MODBUS over TCP/IP
  • Expanded I/O (8 additional outputs and 12 additional inputs)