2. *
Electric machines can be classified in terms of their energy
conversion characteristics.
Generators convert mechanical energy from a prime
mover (e.g., an internal combustion engine) to electrical form.
Motors convert electrical energy to mechanical form.
MOTOR’S TERMINOLOGY
3. *
Distinction can be made between different types of windings characterized by the
nature of the current they carry.
If the current serves the purpose of providing a magnetic field and is
independent of the load, (it is called a magnetizing, or excitation, current)
the winding is termed a field winding.
However, if the winding carries only the load current, it is called an
armature.
WINDING TERMINOLOGY
4. *
A Motor/Generator are made of
Stator: This is the stationary part
Rotor: This is the rotating part
Separated by an air gap
MOTOR CONSTRUCTION
6. When a current carrying conductor is placed in a magnetic field, the
conductor experience a mechanical force.
Direction is given by Flemings left hand rule
Magnitude is F=B.I.L
10. As the coil rotates an emf is induced in each conductor which opposes the
externally supplied armature current, Ia.
The external supply must overcome this emf if the machine is to continue
motoring and deliver mechanical power through its shaft.
Faraday’s Law states that the
emf induced in a conductor = rate of change of flux linkages
Taken over a period of time
Average emf induced in conductor = total flux linkage
total time of linkage
*
INDUCED EMF IN ARMATURE
11. *
This power creates the torque to make the armature rotate.
Electrical torque developed = Electrical power delivered to the armature
in the armature Angular velocity
Mechanical torque|at the shaft = Electrical torque - “Lost” torque|due to frictional and other losses
12. *
DC motors
The three types of DC motors
Shunt wound DC motors
Series wound DC motors
Separately excited DC motor
and their applications
