This article is about speed control of a D. C. Motor. It describe how speed of a D. C. Motor can be controlled.

Hello Friends,

In our current article we will discuss how speed of a D. C. Motor can be controlled i.e. Which factors are controlled to control the speed of the motor ?

From the back e.m.f. Equation of a D. C. Motor we have : E_{b}=PΦNZ/60 A

Where,

P = Number of poles in the machine

Φ = Flux enclosed to a pole

N = Speed of Machine in r. p. m.

Z = Number of Armature Conductors

A = Number of Parallel Paths in D. C. Motor

Also from equivalent circuit of a D. C. Motor we have

V = E_{b}+I_{a}R_{a}

Here V is applied voltage to the D. C. Motor

E_{b} is induced back e.m.f. in motor Armature.

I_{a} is Armature current and

R_{a} is Armature resistance.

E_{b}=V-I_{a}R_{}=NPΦZ/60A

Now we have to control N by changing values of other variables we have

N=(V-I_{a}R_{a})(60A)/PZΦ
This equation decide what should be changed to change the speed of a D. C. Motor. We know that for shunt motor flux is constant i.e. Independent of Armature current while in series motor the flux induced in D. C. Motor depends upon Armature current, so speed control method of both motors will be different.

### Speed Control of D. C. Shunt Motor

We know that in equation

N=(V-I_{a}R_{a})(60A)/PZΦ
The following are constants i.e. Can't be changed

**
**
### Speed Control of D. C. Series Motor

Similarly in D. C. Series Motor, We have the same equation

N=(V-I_{a}R_{a})(60A)/PZΦ
The following are constants i.e. Can't be changed
**
**
Here Φ can be changed by simply increasing or decreasing Armature resistance.

### Speed Control of D. C. Motor ( Series and Shunt Both )

From above discussion it is clear that following can be changed in both series and shunt motors
### Voltage Control Method

From the back e.m.f. Equation E=PNZΦ/60A=V-I_{a}R_{}

We have N=(V-I_{a}R_{a})*(60A/PZΦ)

If Flux kept constant and P, A, I_{a}, R_{a} and Z are already constant so

N=(V-K)*K_{1}

here K and K_{1 } are constant.

Now N is directly proportional to applied voltage. So if applied voltage is increased then the speed of the DC machine will increased and vice versa.### Armature Resistance Control.

If we increase armature resistance then Speed of the motor will be reduced and vice versa.
### Field Flux Control

Increasing flux in a DC motor will reduce speed of the machine and vice versa.

In our current article we will discuss how speed of a D. C. Motor can be controlled i.e. Which factors are controlled to control the speed of the motor ?

From the back e.m.f. Equation of a D. C. Motor we have : E

Where,

P = Number of poles in the machine

Φ = Flux enclosed to a pole

N = Speed of Machine in r. p. m.

Z = Number of Armature Conductors

A = Number of Parallel Paths in D. C. Motor

Also from equivalent circuit of a D. C. Motor we have

V = E

Here V is applied voltage to the D. C. Motor

E

I

R

Normally Armature resistance of a D. C. Motor is of the order of 0.5 ohm.From above two equations we have

E

Now we have to control N by changing values of other variables we have

N=(V-I

N=(V-I

**60 A****P****Z****Φ**

Note : Φ can be changed in D. C. Shunt motor by adding external variable resistance in field winding.

N=(V-I

**60 A****P****Z**

- Applied Voltage V
- Armature Current I
_{a} - Armature Resistance R
_{a} - Flux Φ

- Voltage Control Method
- Armature Resistance Control.
- Field Flux Control

We have N=(V-I

If Flux kept constant and P, A, I

N=(V-K)*K

here K and K

Now N is directly proportional to applied voltage. So if applied voltage is increased then the speed of the DC machine will increased and vice versa.

Article Was Last Updated on **Sunday, March 11th, 2018 At 10:26:50 am**

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