INTRODUCTION
+ MOTOR a machine that converts electrical energy to mechanical energy.
HOW ? ? ? + a current carrying conductor when placed in an magnetic field experiences a mechanical force.
where F=mechanical force vector; I=current; L=length vector of that part of the conductor which is in the magnetic field; B= magnetic field vector.
HOW WILL YOU FIND THE DIRECTIONS??
+ 2 methods:Right Hand Thumb Rule Fleming’s left hand Rule
RIGHT HAND THUMB’S RULE..!!! WHAT’S THIS????
FLEMING’S LEFT HAND RULE!!! .. BUT HOW???
CONSTRUCTIONS OF DC MOTOR+ STATOR- magnetic poles Pole body
Pole winding yoke
carbon brushes
frame or casing
+ rotor- armature core
armature winding
commutator
mechanical shaft
GENERATOR ACTION in dc motor.... CONFUSING???
back emf or counter emfWhat’s that????While rotating, the armature cuts the magnetic field flux producing an emf which opposes applied voltage. In generator, it is called GENERATED EMF.
EQUIVALENT CIRCUIT OF DC MOTOR ARMATURE
Torque equation of dc motor
TYPES OF DC MOTORSSEPARATELY EXCITED DC MOTORSELF EXCITED DC MOTOR SHUNT MOTOR SERIES MOTOR COMPOUD MOTOR (series + shunt)
ARMATURE REACTION – an interesting phenomenon
In simple words, INTERACTION OF ARMATURE FLUX WITH THE FIELD FLUX.2 effects on armature winding flux:-Demagnetising effectCross magnetising effect
The GNA (perpendicular to the pole axis) shifts due to the motoring action and forms a new brush axis , i.e. MNA. Now, this MNA or the resultant armature flux has two components. One, opposite to the original armature flux (de magnetising nature) and the latter, perpendicular to the original armature flux (cross magnetising nature). Thus, the original flux decreases having a great significance in running a dc motor.
Load characteristics of dc motor
Equations require for the load characteristics:-
Effect of Magnetic saturation in B-H curve or Flux-Current curve
So, speed VS current characteristics
SHUNT MOTOR
SERIES MOTOR
COMPOUND MOTORS
So, torque VS current characteristics
SHUNT MOTORS
T
I
SERIES MOTOR
COMPOUND MOTORS
So, torque VS speed characteristic
SHUNT MOTORS
SERIES MOTORS
COMPOUND MOTORS