Experiential learning : Lab Experiment Speed Control of a DC Shunt Motor

Experiential learning : Lab Experiment Speed Control of a DC Shunt Motor

Before discussing the rate control of dc shunt motor, we have to locate the factors affecting the speed of a DC motor.

The velocity equation of a DC motor suggests that,

N α Eb / φ

or N α (V – IaRa)/ φ

But the resistance of armature winding is small. consequently the voltage drops IaRa might be negligible in comparison to the outside supply voltage V. therefore, the expression for the rate can be approximated as follows:

N α V/φ (due to the fact V>> IaRa)

From this expression we can acquire the dc shunt motor pace control methodsas follows:

• The speed is inversely proportional to flux φ.
• It is at once proportional to armature voltage drop (IaRa).
• It is immediately proportional to applied Voltage V.

Speed control of DC Shunt Motor

So through various this kind of parameters, it's far viable to exchange the rate of DC shunt motor. relying at the parameter being managed, strategies of pace manipulate of shunt DC Motor are classified as follows:

Flux control method 

The set up for speed control of DC shunt motor using flux manipulate approach is proven within the parent. a good way to alternate the speed, we should change flux. this could be done via converting the field modern. the sphere contemporary can be changed with the aid of changing the rheostat R linked in collection with the sphere.

On the time of starting the motor, we need to run the motor slowly, consequently, the flux need to be maximum, because,

N α  1 / φ 

To acquire maximum flux at the start, the field modern-day must be maximum at the time of beginning. To acquire this, the fee of rheostat (R) must be minimal.  

The rate of DC shunt motor can be varied by means of various the sphere cutting-edge. As we increase the resistance R of the rheostat, the sphere current Ish decreases.  So the flux φ decreases. This results in growing the speed of the motor. because the R is elevated, the velocity increases.

We can use this method to manipulate motor pace above its rated price. it's miles the maximum business technique. there's a restriction to the most obtainable pace by using this approach because of bad commutation at week fluxes.  most commonplace most to minimal pace ratio is 6:1.

Speed Control of DC Shunt Motor by Armature

The set up for speed manage of DC shunt motor by armature voltage manage approach is proven in the discern. A rheostat is hooked up in series with armature winding. with the aid of various the price of R we will range the voltage throughout the armature.

Because velocity N is at once proportional to armature voltage, it is feasible to change the velocity via converting the value of rheostat R.

We will use this approach to govern motor speed underneath its rated cost. however it's far neither green nor competitively priced approach due to the fact, in this technique, speed is decreased at the cost of energy loss in rheostat (Ia2R).