An electric motor is a machine which convert electrical energy in to mechanical energy .Its principle is that when a current carrying conductor is place in a magnetic field its experience a force which direction is given by Fleming left hand Rule and magnitude is given by F=BIL Newton
There is no difference between the D.C Generator and D.C Motor .The same dc Generator can be used as a Dc motor .
When a voltage is applied to the Dc motor ,current will pass in to positive brushes through commutator into the armature winding .Actually the motor armature winding is identical to that of Generator armature winding .Therefore the conductor under north pole carry current in one direction and conductor under south pole carry current in opposite direction.When armature carry current its produce magnetic field which will interact with the main field as a result there is a force developed on the conductor which tend to turn the armature or rotor .
The rotating armature conductors ina motor cut the flux from the poles, so an emf is induced in armature .According to the Lenz’s Law tgis emf opposed the applied emf to the motor and this emf is known as Back emf Eb and is given by
Where Z=Total No of armature conductors
A=No of Parallel path in armature
N= Speed of rotation
P=No of Pole
$=Flux per Pole
Voltage Equation of Motor
The basic Voltage equation of motor is expressed by
Where v= P.d applied ti the brushed in volt
Eb is Zero when the motor is at standstill or not start.
The torque of Dc motor is given by
F =2πr X N Watts
= Torque X Angular Velocity
P= T.ω watts
Where f =circumferential force (Newton)
r=radius of the pulley
Torque = Fx 2 π r joule
Where N is the speed in RPM
Speed of Motor