DC Motor | Principal Operations | Construction | Parts | Yoke | Poles, Poles shoe and pole core | Field Winding | Armature Core

Principle of Operation of a DC Motor :

The operating principle of a DC motor can be stated asi follows :
When a current carrying conductor is placed in a magnetic field, it experiences a force.
In case of a DC motor, the magnetic field is developed by the field current i.e. the current flowing in the field winding. The armature winding 1s connected to an external dc source, hence it plays the role of the current carrying conductor placed in the magnetic field. i
Due to the force exerted on it when placed in the magnetici field, it starts rotating and the armature starts rotating. The direction of rotation depends on the direction of the magnetic field produced by the field winding as well as the direction of magnetic field produced by the armature, as discussed in section 5.1.3 (Fleming's left hand rule).

Construction of a DC Machine

Yoke

Important Parts of a DC Machine :

The important parts of a DC mschine are as follows: Armature Commutator, brushes and gear

 Yoke is also called as frame. It provides protection to thei rotating and other parts of the machine from moisture, dust i etc.
Yoke is an iron body which provides the path for the flux. This is essential to complete the magnetic circuit. It provides the mechanical support for the poles. Materials used for yoke are basically the low reluctancei materials such as cast iron, silicon steel, rolled steel, cast steel etc. i

Piles, Pole Shoe and Pole Core :

 The important points about the poles are as follows: A pole of a dc machine is an electromagnet. The field winding is wound over the poles.
Poles produce the magnetic flux when the field winding is excited.
Pole shoe is an extended part of a pole. Due to its typical shape, it enlarges the area of the pole.
Due to this enlarged area, more flux can pass through the aur gap to armature.
A kow reluctane magnetic matenal stch as cast steel or cat i iron is used for the constncton of a Dole or Dole shoe The construton of poles is done using the laminations ou particular shape This is to reduce the power loss due to edd

Field Winding

The coils wound around the pole cores are called field coils. The field coils are connected in series with each other to form the field winding.
Current is passed through the field winding in a specific direction. to magnetize the poles and pole shoes. The magnetic flux o is thus produced in the air gap between thei pole shoes and armature.
The field winding is also called as Exciting winding. The material used for the field conductor is copper. Due to the current flowing through the field winding alternate N and S poles are produced. Which pole is produced at a particular core is decided by the right hand thumb rule for a current carrying circular conductor.

Armature Core:

The important information about armature core is as follows; Armature core is a cylindrical drum mounted on the shaft. It is provided with a large number of slots all over its perphery.
All these slots are parallel to the shaft axis. Armature conductors are placed in these slots.