Saturday, July 12, 2014

DC Motors working principle; Direct current motors


There are two types of supplies and there are two types of motors known as :-
1. AC Motors
2. DC Motors

Here we will discuss about DC motors working principle.

These DC motors works on the principle that when there is a current carrying conductor put in a magnetic field it will experiences a torque. This is called motoring activity. 

If the direction is reversed. Then this will act as a generator.
Electrically structurally and construction wise a direct current generator is just the reverse, although it is precisely just like a DC motor. 

Block diagram for the same is shown below. Here we derive mechanical energy in the output signal interface and provide electrical energy to the input signal interface. i.e. is called as DC motor and for DC generator it is reverse i.e. mechanical at I/p and we get electrical energy at the O/p.



Direction of rotation of DC motor is given by Fleming left hand rule



The direct current motor's input and output signal interface variables are connected by the parameter K.


So in the image above we can well comprehend that motor is simply the contrary occurrences simply by reversing the interfaces and we are able to derive both motoring and producing process from an identical machine.

In-Depth Description

To comprehend the DC motor in details let's see DC motor diagram:-


The circle in the middle represents the direct current motor, on which is mounted the brushes, where the outside terminals are connected by us . On the terminal that is mechanical we've got a rotating shaft coming from the Motor, and linked to the armature, and the armature -rotating shaft is coupled to the mechanical load. Now, allow the input signal voltage E, is used across the brushes. Electric current which flows through the rotor armature in existence of the magnetic field, generates a torque Tg.

The back emf like in case is represented by

Eb= PφZN             ----- (i)
         60A

P = no of poles
φ = flux per pole
Z= No. of conductors
A = No. of parallel paths
and N is the speed of the DC Motor.
A direct current motor rotates that's, it results in the creation of back Emf. Now lets symbolize the rotor rate by omega Eb .

Ia= E-Eb
       Ra

Then when the use of load reduces the rate, Eb decreases. So the voltage difference that means E - Eb increases. As a result of this increased voltage difference, armature current will raise and thus torque and thus rate increases. So there is a DC Motor effective at keeping the exact same rate under variable load.

Now armature current Ia is symbolized by


T= KI and Eb= Kw

Where T= Torque at O/P in case of motors ; K is proportionality constant

Now at beginning, rate w = 0 at beginning Eb = 0 so.


Putting Eb=0 we get 

Ia=  E
        Ra
                             

Since the armature is not large, this motor has an extremely high starting current in the lack of back Emf. Consequently we must use a starter.

The back Emf begins being produced and slowly the present declines picks up rate, as the motor continues to rotate.