Motor Protection Device

The multifunction numerical motor protection device provides complete protection of low voltage motors. The device has been developed keeping in view of varied customer needs and various applications of motors. Accordingly, the motor protection device incorporates the following:

  • Precise estimate of the thermal image of motor for varying conditions of starting, running, overload, stopping, unbalance conditions. The negative sequence current calculations are taken into account for unbalance current conditions.
  • Continuous monitoring of thermal capacity used and in case of power failure the last value of accumulated thermal capacity prior to power interruption is stored.
  • Six thermal overload curves – 2.5C, 5C, 10C, 15C, 20C and 30C covering the complete range of motor applications.
  • Motor start lockout feature inhibiting start of the motor, in case of non-availability of sufficient thermal reserve to complete the acceleration.
  • In built Insulation resistance check function prior to start of motor to give a preliminary indication of the condition of insulation, so that the user can take appropriate action for low value of insulation resistance.
  • Automatic setting of parameters function, which would set all the protection parameters only on entering the rated full load current as per the motor name plate details.
  • Annunciation, in case, the motor fails to stop after the protection device issues trip command.


The salient features of device are:

  • LED Seven Segment Display, brighter pixilation and longer life than LCD
  • Continuous scanning and display 3 phase currents and thermal capacity used
  • Annunciation for each type of fault
  • Numerical Algorithm for fast, reliable operation
  • Thermal Overload curves selectable as per requirement, Excellent accuracy and long-time stability of thermal curves due to complete software-based implementation
  • Customized protection CT as per load requirement supplied with the relay
  • Continuous self- supervision and fail-safe operation
  • Man-Machine interface through keypad
  • Upto five event trip records, FIFO based (with date and time stamping in model – HLEDx)
  • Reset Inhibit function, Hour Counter, Online calibration, Password facility (on demand)
  • Robust mechanical design and adequate IP 54 degree of protection by enclosure which is shock proof nonmetallic screw less unit


The device provides protection against the following:

  • Overload
  • Short Circuit
  • Under Current
  • Unbalanced current
  • Locked Rotor
  • Earth Fault
  • Single Phasing (Phase Loss)


Following optional protections/ functions are available based on selected variant of MPD:

  • Phase reversal
  • Over Temperature (Thermistor Based)
  • Over Voltage & Under Voltage
  • Pre-Trip Alarm for thermal Overload or Definite time overcurrent
  • PF, KW & KWH measurement
  • Startup Counter with trip facility
  • SSR Output for Short Circuit Protection
  • Insulation Resistance check facility prior to start of motor
  • Data communication over MODBUS RTU protocol between Motor Protection level and higher-level data acquisition for reporting, parameterization, fault annunciation, reset function and hour counter
  • 4-20mA Analogue output
  • Hour Counter
  • Online Calibration
  • Password Facility


Technical Specifications

Rated Current                                                                                    0.2 to 250 A (Six CT ranges), 50 to 500 A, 100 to 1000 A


Rated Frequency                                                                              50 Hz/ 60Hz


Auxiliary Voltage                                                                              110 / 230 /415 V AC


Mass of the device                                                                            500gms. (approx.)


Mounting type                                                                                  Flush mounted

Dimensions (LxWxD)                                                                      96 x 96 x 65 mm


Panel Cutout                                                                                      92 x 92 mm


CT Range (Based on Motor full load current), Amperes         0.2-6.25, 0.4-12.5, 0.8-25, 2-62.5, 4-125, 40-250,


CT Range (Based on Motor full load current), Amperes        50-500 A, 100-1000 A (in Model – HLEDx)



Metering Specifications

Line Currents measurement Range                                            0.2 to 2000A, 50 to 8000A (in Model – HLEDx)


Accuracy                                                                                           +/-1% (0.5 – 1.5 x FLC), +/-5% beyond 1.5 x FLC


Earth Fault Current Measurement Range                                1A to 25A, 1A to 100A (in Model – HLEDx)


Accuracy                                                                                           +/- 1% or 1A whichever is greater



Monitoring Specifications

Records                                                                                             Stores last five fault records


Hour Meter                                                                                      Records and stores total operational hours


Operation Counter                                                                         Records and stores number of starts



Thermal Overload curve selection                                              2.5C, 5C, 10C, 15C, 20C and 30C (six curves)


Thermal Overload setting range                                                 0.2 to 250A, HLEDx – upto 1000 A


Thermal Overload Operating time                                             as per thermal curve selected


Under Current feature                                                                   Enable/ Disable


Under Current setting range                                                        30% to 80% FLC


Under Current operating time                                                    1 to 60 sec


Locked Rotor setting range                                                          As per current range selected, pick up 3 x FLC


Locked Rotor operating time                                                       1 to 10 sec. (in Model – HLEDx)


Locked Rotor pick up delay time (during starting)                 1 to 30 sec.


Earth fault feature                                                                          Enable / disable

Earth fault feature                                                                          Enable (Residual flux -CBCT used)

Earth fault feature                                                                          Disable – (Vector summation)


Earth fault setting range                                                               10% to 40% FLC


Earth fault operating time                                                            0.5 sec to 3 sec.


Earth fault pickup delay (during starting)                               Enable or disable

(When enable; earth fault function will not operate during motor starting for 10 seconds)


Short Circuit setting range                                                           As per current range selected, pick up 8xFLC


Short Circuit operating time                                                        Instantaneous, 0.1 to 3.0 sec (in Model – HLEDx)


Single phasing setting                                                                   Enable or Disable


Single phase operating time                                                        2 sec, 1 to 10 Sec (in Model – HLEDx)


Unbalance protection                                                                    Enable or Disable


Unbalance protection setting range                                           10% to 40%


Unbalance protection operating time                                        3 to 10 sec.


Reset Inhibit time                                                                            1 to 999 sec.


In eLEDx model below functions are also available:


Low voltage setting range                                                            100 to 500 V


Low voltage operating time                                                         1 to 60 sec.


High voltage setting range                                                           100 to 500 V


High voltage operating time                                                        1 sec (default)


Under load setting range                                                              0.115 to 144 kW


Under load operating time                                                           1 to 60 sec.



Data Output                                                                                    RS 485 MODBUS RTU, Baud Rate–9600, Word length – 8


Analog Output                                                                                4-20mA


Insulation tests

Dielectric test, IEC 60255- 5                                                        2kV, 50hz, 1 min.

Impulse voltage test, IEC 60255-5                                             5kV, 1.2/50 Hz microsec., 0.5j

Insulation resistance measurement, IEC 60255-5                > 100 M ohm, 500V DC


Environmental conditions

Ambient service temperature                                                      0 deg.C to + 55 deg.C

Transport and Storage temperature range                              0 deg.C to +70 deg.C

Degree of protection by enclosure, panel mounted              IP 54 (Front side of the Device)