Electric Motors
Electric Motors

Speed regulation of Dc motor (in details with equations)

Speed regulation of Dc motor

speed regulation of dc motor … We know that the speed of any motor decreases automatically when we apply a load to it, and to keep the constant speed we should maintain the difference between no load and full load speed (speed regulation)  very less.

And the speed regulation of the different types of Dc motor is:

Speed regulation of Dc motor

And to understand the speed regulation, we should start with the speed of the Dc motor.

The speed of a Dc motor:

From the EMF equation:



N: speed of rotation.

P: number of poles.

A: number of parallel paths.

Z: total number conductors in the armature.

Speed of a Dc motor

So, the speed will be:


while A, P, and Z are constant the speed will be:


From this equation, we deduce that:

  • The speed is directly proportional to the EMF.
  • While we add a load to the motor it produces more torque to overcome the added load.
  • As the torque is proportional to the current so the armature current increases.
  • Also to produce more torque we will increase the pole magnetic field and that can be achieved when the armature speed decreases.
  • and in order less back EMF produced in the armature.
  • When the back EMF decreased a more current flow through the armature and causes an increase in the magnetic field strength which means that the speed is proportional to the armature resistance or the speed is inversely proportional to the flux  (Φ).

Speed regulation of Dc motor:

After we know the speed of the Dc motor we can define the speed regulation of Dc motor as the change in the speed from no load to full load expressed as a fraction of the full load speed,  and the per unit speed regulation will be:

per unit speed regulation

So, the percentage(%) speed regulation will be:

percentage speed regulation

And from the above equations,  we can say (in conclusion) that the motor which mainly has a constant speed has a good speed regulation.

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