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Speed control methods of DC motor - Electrical Diary

What is a Starter?

The starter is an electrical device that is used to start a dc motor. the purpose of using a starter to start a dc motor is that the starter gives smooth and control the start of the dc motor. if we do not use the starter to start a motor then during the starting period it will draw a heavy current from a source which will generate a huge amount of heat and it will damage the armature.
speed control method of Dc shunt motor

There is a relation between the back emf and speed of the motor and this relation is given as

E(back emf) =NPΦZ/60A------------------(1)
and also applied terminal voltage and armature current are  relates as follow:-

V = IaRa + E

E = V - IaRa -------------(2)
Ra = Armature Resistance
Ia = Armature Current
N = Speed of the motor
P   = Number of Pole of the motor
Φ  = Flux Per Pole
Z = No.of Conductor
A = No of Parallel Path

If we arrange the above give equation (1) then we got a new equation like this.

N =60AE/PZΦ----------------(3)

And this calculated Speed is given in RPM(Revolution Per Minute). For a given motor of fixed dimension parameter A,P, and Z are constant. hence if we remove all these constant by a new constant then the speed of the motor will be given as

N = K(E/Φ)------------------------------------(4)

after using equation (2) speed of the DC Motor can be given as

N = K(V -IaRa)/Φ -------------(5)

From equation (5) it is clear that the speed of the DC motor is a function of armature current (Ia), armature resistance (Ra), and Flux Per Pole. By adjusting all these parameters, the Speed of the dc motor can be easily Control. By using the different -different parameters, different types of speed control techniques are used to control the speed of the DC motor. Some of the common methods which are used to control the speed of DC motor are:-
  • Variation of resistance in the armature Circuit.this method is called armature resistance control. Some time  Rheostatic Control.
  • Variation of field flux. This method is called Field Flux Control.
  • Variation of applied Voltage .this is called armature voltage control.
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