# Speed Control of DC Shunt Motors

- Link: https://studyelectrical.com/2013/11/speed-control-of-dc-shunt-motors.html
- Published: 2013-11-20T16:04:00+00:00
- Author: 

![SPEED%2BCONTROL%2BOF%2BDC%2BSHUNT%2BMOTOR](https://4.bp.blogspot.com/-p_s4Lp39Eng/
VpPdnbGQpNI/AAAAAAAABu0/joAc8R-RXLY/s1600/SPEED%2BCONTROL%2BOF%2BDC%2BSHUNT%2BMOTOR.
jpg)

The different methods of speed control in DC shunt motors are explained below,

 1. Flux Control Method
 2. Armature Control Method
 3. Voltage Control Method
 4.  * Multiple Voltage Control
     * Ward Leonard System

> [Related Topic : Speed Control of DC Series Motor](http://www.studyelectrical.com/2013/11/speed-control-of-dc-series-motors.html)

## Flux Control Method

Speed is inversely proportional to flux. So by varying flux, we can change the speed
of the motor. 

In this method, a **variable resistance (known as shunt field rheostat)** is placed
in series with shunt field winding.

 

[[

 Flux control Method

The field rheostat reduces the shunt field current Ish. So the flux also gets reduced.
There the speed can be raised above normal speed as shown in the figure. 

Generally, this method permits to increase the speed in the ratio 3:1. Wider speed
ranges tend to produce instability and poor commutation.

## Armature control method

The concept behind this method is that the back emf and the speed of the motor can
be changed by varying the voltage across armature V. 

![Armature Control Method](https://3.bp.blogspot.com/-_KiGwQzY3KE/UqfdtXkPvOI/AAAAAAAAArY/
R8nJRmM095I/s640/Armature_control_method__1386732860_12060.jpg "Armature Control
Method")

 Armature Control Method

 

A variable resistance **Rc ( controller resistance )** is placed in series with 
the armature as shown in the figure.

Since Rc is introduced, the voltage drop is increased and hence [back emf  [](https://studyelectrical.com/2015/02/back-emf-and-significance-in-dc-motor.html)
Eb = V – IaRa] decreases.

Also  N **∝**** **Eb, therefore speed decreases.

The highest speed is when Rc=0 i.e, normal speed. Hence, this method can only provide
speeds below the normal speed.

## Voltage control method

_There are some disadvantages for flux control method and  armature control method
such as poor speed regulation and poor efficiency._ Voltage control method overcome
these problems.

In this method, the voltage source supplying the field current is different from
that which supplies the armature. 

This method is used for large size motors since it is very expensive.

### 1. Multiple voltage control

In this method, the shunt field of the motor is connected permanently across a-fixed
voltage source. 

The armature can be connected across several different voltages through a suitable
[switchgear](http://www.studyelectrical.com/2015/07/what-is-switchgear-features-components-hv-mv-lv.html).
In this way, voltage applied across the armature can be changed. 

The speed will be approximately proportional to the voltage applied across the armature.
Intermediate speeds can be obtained by means of a shunt field regulator. 

### 2. Ward Leonard system

Adjustable voltage is obtained from the system shown in below diagram. 

[⌊Ward Leonard system 1386733463 87666⌉⌊Ward Leonard system 1386733463 87666⌉[

The armature of the shunt motor M (whose speed is to be controlled) is connected
directly to a d.c. generator G driven by a constant-speed a.c. motor A. 

The field of the shunt motor is supplied from a constant-voltage exciter E. The 
field of the generator G is also supplied from the exciter E. 

The voltage of the generator G can be varied by means of its field regulator. By
reversing the field current of generator G by controller Fc, the voltage applied
to the motor may be reversed. 

Sometimes, a field regulator is included in the field circuit of shunt motor M for
additional speed adjustment. With this method, the motor may be operated at any 
speed upto its maximum speed.          

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