6. • Yoke : It provide mechanical Support for poles & protection.
• Pole Shoe : It is extended part of pole & enlarge area of pole.
• Field Winding : When Current is passed through field winding it electro
magnetize the poles which produce necessary flux.
• Armature Core & Winding : It provide path of low reluctance to the flux
produced by field winding & when armature winding is rotated using prime
mover. the magnetic flux and voltage gets induced in it.
• Commutator : It Convert alternating current, collects the current form
armature conductor and pass it load with the help of brushes & provide
unidirectional torque for dc motor.
7. Working Principle
• In a basic dc motor, an armature is placed in between magnetic poles. If the armature
winding is supplied by an external dc source, current starts flowing through the
• As the conductors are carrying current inside a magnetic field, they will experience a
force which tends to rotate the armature. Suppose armature conductors under N poles
of the field magnet, are carrying current downwards (crosses) and those under S poles
are carrying current upwards (dots).
• By applying Fleming’s Left hand Rule, the direction of force F, experienced by the
conductor under N poles and the force experienced by the conductors under S poles
can be determined. It is found that at any instant the forces experienced by the
conductors are in such a direction that they tend to rotate the armature.
• DC Shunt Motors is a constant speed motor. (Lathes, Drills, Boring
mills, Shapers, Spinning and Weaving machines)
• DC Series motor is a variable speed motor. (Electric traction, Cranes,
Elevators, Air compressor, Vacuum cleaner, Hair drier, Sewing
• DC Compound motor, thedifferential compound motors are rarely
used because of its poor torque characteristics. (Presses Shears,
• High initial cost
• Increased operation and maintenance cost due to
presence of commutator and brush gear
• Cannot operate in explosive and hazard conditions
due to sparking occur at brush ( risk in commutation
• Transformer is a device consisting of two or more coils that are used to
couple electrical energy from one circuit to another while maintaining
electrical isolation between the two.
• Primary Winding – Winding of the transformer that is connected to the
• Secondary Winding – Output winding of the transformer that is connected
to the load.
13. Working Principle
• Mutual inductance
• Mutual Inductance – The ability of one inductor’s magnetic field lines
to link with another inductor.
15. Classification of transformer
• As per phase:
1. Single phase
2. Three phase
• As per core:
1. Core type
2. Shell type
• As per cooling system:
2. Air cooled
3. Oil cooled
16. Step up transformer
• A step up transformer is a type of transformer that
increases voltage from primary to secondary (more
secondary winding turns than primary winding turns) is
called a step up transformer.
17. Step down transformer
• A step down transformer is a type of transformer that decreases
voltage from primary to secondary (less secondary winding
turns than primary winding turns) is called a step down