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2C73 High Impedance Differential Relay

The 2C73 relay provides high speed differential protection for various items of power system plant including generators, busbars, motors & the individual windings of power transformers. The 2C73 is also suitable for restricted earth fault applications. The relay measuring element is basically an attracted armature unit of simple & rugged construction. The operating coil of this unit is connected in series with an inductor & capacitor forming a resonant circuit. These components are energised from a transformer which is tapped to provide current setting using the front panel mounted plug bridge. Removal of the setting plug bridge will result in the maximum current tap setting. The relay circuit is tuned to the supply frequency & rejects harmonics produced by current transformer saturation. A slight time delay on operation is provided to ensure stability on heavy external faults.


  • High speed operation
  • High sensitivity
  • High stability for through faults
  • Operating current set using
  • 7 position plug bridge
  • Optional 1A or 5A CT input
  • Tuned to 50Hz or 60Hz
  • 25ms operation at 5x setting
  • Hand reset mechanical flag
  • 2 heavy duty N/O trip contacts
  • Rugged attracted armature sensing elements
  • Use 3 independent units for 3 phase applications
  • Size 2M28-S draw out case
  • Made in Australia

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©1998-2012 Relay Monitoring Systems Pty. Ltd.      ACN 052 484 483     ABN 76 052 484 483

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