Motor No load Calculator:
Choose the motor type, then enter the full load current of the motor. Then press the calculate button to motor get no-load current. Also, the motor rated below 3 HP the motor will take up to 40% to 60% of the full load current at the delta connection.
Motor no-load current Calculations:
Motor no-load current is nothing but a measuring the motor current without connecting any mechanical loads in short form “shaft will be driven by hand freely”. Also at no load, the power factor becomes very poor. Since motor draws high reactive current rather than the active current. Therefore, the normal current calculation formula will not help you.
Let we find out the no-load calculation formula…
Star Connected motor:
It means the three-phase motor will be connected in star connection (one end short and another end supply). The motor will take 10% of the full load current. therefore,
No load current at star connection = 0.1 x Motor Full load current.
I(No-load) = 10% x I(FLA)
Delta connected Motor:
It means the motor will be connected as the delta. (all winding series-connected and the junction will be connected to the power supply).
No load current at delta connection = 0.3 x Motor Full load current.
I(No-load) = 30% x I(FLA)
Look at the difference between star-connected motor and delta connected motor, do you know why this difference?
If you connect the motor at star connection means, the applied voltage will be reduced, hence as the voltage is proportional to the speed of the motor. The motor will run at 60% of the full speed. While decreasing the speed along with the voltage, the motor current will be decreased and the motor draws the current to remain the same speed.
If you connect it in delta connection means, the winding will get full voltage, there is no speed drop. Hence the motor draws 30% of the current to maintain the full speed.
For DC Motor:
The DC motor no-load current will be 25% of the full load current at the full speed (not at the base speed). hence
No load current for DC motor = 0.25 x Motor Full load current.
Benefits of Finding Motor No-load current:
- Testing the motor with low rated testing equipment. For example, you would like to run a 50HP motor at the no-load condition at the maintenance area, then you cannot shift entire starting equipment from the service area to the maintenance area. Instead of that by calculating no-load current of the 50HP motor (it will be 6 to 10 Amps), you can design low rated starting equipment (i.e starter, cables etc) to start the motor at the maintenance floor itself.
- The no-load current is used to improve the winding resistance (to improve the megger value).
Note: All the above calculation is my personal experience.
Note: All the above calculations are my personal experience.