# Speed Control Of DC Series Motors

- Link: https://studyelectrical.com/2013/11/speed-control-of-dc-series-motors.html
- Published: 2013-11-22T12:47:00+00:00
- Author: 

Although a far greater percentage of electric motors in service are ac motors, the
dc motor is of considerable industrial importance.

The principal advantage of a dc motor is that its speed can be changed over a wide
range by a variety of simple methods. Such a fine speed control is generally not
possible with ac motors.

In fact, fine speed control is one of the reasons for the strong competitive position
of dc motors in modern industrial applications.

The **speed control of d.c. series motors** can be obtained by two methods

 1. **Flux control method**
 2. **Armature-Resistance control method**.

![Series Motor Speed Control Methods](https://studyelectrical.com/wp-content/uploads/
2013/11/series-motor-speed-control.png)

Series Motor Speed Control Methods

**The armature-resistance control method is mostly used.**

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

## Flux control method

In this method, the flux produced by the series dc motor is varied. The variation
of flux can be achieved in the following ways:

 1. **Field Diverters**
 2. **Armature Diverter**
 3. **Tapped Field Control**

### 1. Field diverters

In this method, a variable resistance (called field diverter) is connected in parallel
with series field winding.

A part of the line current passes through this diverter and thus weakens the field.
Since **N ∝ 1/ϕ **, speed also varies with field flux.

![Field diverters](http://1.bp.blogspot.com/-fDJMX2uapWU/UpA7xYaXSBI/AAAAAAAAAp4/
GQgVgvzoYiY/s320/Untitled.jpg "Field diverters")

Field diverters

The lowest speed obtained by this method is the normal speed of motor when the current
through diverter is zero, ie, diverter open circuited.

### 2. Armature diverter

In order to obtain speeds below the normal speed, a variable resistance (called 
armature diverter) is connected in parallel with the armature of dc series motor.

The diverter reduces the armature current. As a result flux get increased. So the
speed decreases since **N ∝ 1/****ϕ**.

### 3. Tapped field control

In this method, the flux is reduced (and hence speed is increased) by decreasing
the number of turns of the series field winding.

![Tapped field control](http://4.bp.blogspot.com/-5oyCX2F_PAU/UpXgHogQxDI/AAAAAAAAAqs/
uPRHlZ9KCk4/s320/Tapped+field+control.jpg "Tapped field control")

Tapped field control

The switch S can short circuit any part of the field winding, thus decreasing the
flux and raising the speed.

With full turns of the field winding, the motor runs at normal speed and as the 
field turns are cut out, speeds higher than normal speed are achieved.

## Armature-resistance Control

In this method, a variable resistance is directly connected in series with the supply.
This reduces the voltage available across the armature and hence the speed falls.

[⌊Armature-resistance Control⌉⌊Armature-resistance Control⌉[

Armature-resistance Control

By changing the value of variable resistance, any speed below the normal speed can
be obtained. This is the most common method employed to control the speed of d.c.
series motors.

### Related posts:

No related posts.