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Saturday, 28 December 2019

How DC MOTOR Works? and Its Construction, Types, Applications.

ELECTRIC  MOTORS


  • An electric motor is an electrical machine that converts electrical energy into mechanical energy.
  • Most electric motors operate through the interaction between the motors magnetic field and electric current in a wire winding to generate force in the form of rotation of a shaft. 
  • Electric motors can be powered by direct current (DC) such as from batteries, motor vehicles or rectifiers.
  • And powered by an alternating current (AC) called ac motors.

DC MOTORS

DC MOTOR
DC MOTOR
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DC motor is  electrical machines that converts direct current electrical energy into mechanical energy.

Construction of DC Motor

A DC motor or a DC machine consists of two windings namely field winding and armature winding. The field winding is stationary and armature winding can rotate.
 
The field winding produces a magnetic flux in the air gap between the armature and field windings and the armature is placed in this magnetic field.


 The construction of DC motor or machine is shown in Figure.





construction of dc motor
Yoke
  • The yoke acts as the outer cover of a DC motor and it is also known as the frame. 
  • The yoke is an iron body, made up of low reluctance magnetic material such as cast iron, silicon steel, rolled steel etc
  • It provides mechanical protection to the outer parts of the machine
  •  It provides low reluctance path for the magnetic flux. 
 Pole and pole shoe
  • The pole and pole shoe are fixed on the yoke by bolts. 
  • These are made of thin cast steel or wrought iron lamination which are riveted together. Poles produce the magnetic flux when the field winding is excited. 
  • Pole shoe is an extended part of a pole. Due to its shape, the pole area is enlarged and more flux can pass through the air gap to the armature.
Field Winding 
  • The coils around the poles are known as field (or exciting) coils and are connected in series to form the field winding. 
  • Copper wire is used for the construction of field coils. 
  • When the DC current is passed through the field winding, it magnetizes poles which produce magnetic flux. 
Armature Core
dc motor construction
  • It is a cylindrical drum and keyed to the rotating shaft. A large number of slots are made all over its periphery, which accommodates the armature winding. 
  • Low reluctance, high permeability material such as cast iron and cast steel are used for armature core. 
  • The laminated construction is used to produce the armature core to minimize the eddy current losses.

Armature Winding
  • The armature winding plays very important role in the construction of a DC motor because the conversion of power takes place in armature winding. 
  • On the basis of connections, there are two types of armature winding named:                                               Lap winding                                                                                                                                     Wave Winding
 Commutator
  • It is a mounted on the shaft. It is made up of a large number of wedge-shaped segments of hard drawn copper, insulated from each other by a thin layer of mica. 
  • The commutator connects the rotating armature conductor to the stationary external circuit through carbon brushes. 
  • It converts alternating torque into unidirectional torque produced in the armature.
Brushes

  • The current is conducted from voltage source to armature by the carbon brushes which are held against the surface of commutator by springs. 
  • They are made of high-grade carbon steel and are rectangular in shape.
Bearings
  • The ball or roller bearings are fitted in the end housings. 
  • The friction between stationary and rotating parts of the motor is reduced by bearing. 
  • Mostly high carbon steel is used for making the bearings as it is very hard material.
Working principle of DC Motor 
  • "Whenever a current carrying conductor is placed in a magnetic field, it experiences a mechanical force". 
  • The direction of this force is given by Fleming's left-hand rule and its magnitude is given by 
  • F = BIL. 
                 Where,   B = magnetic flux density, 
                                I = current and 
                                L = length of the conductor within the magnetic field.
Fleming's Left Hand Rule: If we stretch the first finger, second finger and thumb of ur left hand to be perpendicular to each other, and the direction of magnetic field is represented by the first finger, direction of the current is represented by the second finger, then the thumb represents direction of the force experienced by the current carrying conductor.
DC Motors working
DC Motors working
Types of DC Motor

DC motors are usually classified on the basis of their excitation configuration, as follows -
  • Separately excited (field winding is fed by external source)
  • Self-excited -
    • Series wound (field winding is connected in series with the armature)
    • Shunt wound (field winding is connected in parallel with the armature)
    • Compound wound -
      • Long shunt
      • Short shunt
Applications 
  • Blowers and fans
  • Centrifugal and reciprocating pumps
  • Cranes 
  • Hoists, elevators 
  • Rolling mills
  • Drilling machines



1 comments:

Dexter Magnetic Technologies said...

This article is charming. The people who need this information about it. It's enlightening and sensible for those all. Permanent magnets

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