3A400 Pilot Wire Supervision System


The 3A400 concept is based on the need to improve the performance of existing pilot wire protection schemes by increasing reliability & availability as well as adding an over current guard function. With the 3A400 this can be achieved at considerably lower cost than the replacement of the existing proven protection relays & change over to a fibre optic communication channel. A revised protection scheme using the 3A400 comprises the following functional elements:

  • The existing current differential protection relays;
  • Pilot wire supervision system to monitor the pilot wire integrity;
  • High voltage rated series capacitors to isolate the DC supervision voltages from the circulating AC protection signals; Shunt resistor to increase fault current setting;
  • Pilot wire fail alarm contact provided at both ends of the protection scheme; Self supervision circuitry to monitor & alarm in event of system failure;
  • A control panel for setting & displaying the system status.


  • Integrated pilot wire supervision system for current differential protection schemes
  • Operates using conventional metallic pilot wire (0 to 2K Ohm pilot resistance)
  • Inherent 5KV or 15KV isolation No external components required
  • Integrated pilot protection discrimination timer
  • Extensive self supervision features to ensure functional integrity
  • Supervision alarm contacts provided at both ends of pilot
  • Simple to set up & commission
  • Flush or 4U 19″ rack mounting
  • M4 screws for control wiring
  • M5 studs for pilot cable connection with clear protective isolation cover
  • Made in Australia



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