dc motor- load characteristics

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