Motor Protection Device (MPD)

Why Micro Computer Electronic Relays are Preferred?

  • It is Established fact that Thermal BI-METAL Relays cannot detect over loaded conditions much above 10%.
  • That such device loses their accuracy with time due to their electro-mechanical wear. (They need to be replaced every 1 to 2 year if any token of accurate protection is required.)
  • That devices do not accurately reflect the heat buildup in a motor and that when they in like manner do not reflect an accurate required cooling period before the motor may be safely restarted.
  • Such device will trip on a phase loss condition unless the motor happens to be running close to full load.
  • As thermal overload relay operates on thermal principle, it consumes costly energy about 60W of each relay.
  • 20% motor burn out are due to faulty, spurious unmatched overload relay including its heating element failure.
  • The breakdown analysis of the motor failure reveals that 50% are due to single phasing & 50% due to bearing failure, jamming & locked rotor condition which clearly established the fact that thermal over load relays does not provide protection at all against bearing failure & single phasing.
  • Due to repeated failure of motor owing to bearing failure, the bearing housing becomes loose motor shaft worn out, which add to imperfection of rotating part inviting further breakdown, increased no load losses, added frictional loss, energy loss & next breakdown.


  • Single phasing, Unbalanced, Over load, Earth Leakage, Locked Rotor, Short Circuit, Under Current, Phase reversal, Thermistor over temp. Protection etc.
  • Provides different curves for accurate overload tripping on the bases of starting time current of motor.
  • Annunciation indicates the type of fault.
  • Man - Machine Interface through keypad & Display.
  • Digital Ameter with auto scanner for three phase current and Earth leakage current.
  • Available in different range from 0.2 to 2000 A.


  • Last Fault History
  • Number of motor start - stop count to prevent motor heating
  • Star - Delta Timer
  • Detachable display console
  • Auto Restart
  • Inbuilt Energy Saver as Automatic Delta to Star Convertor
  • Serial Communication Port RS485
  • Real-Time Clock