Construction:-
DC Motor
1.Magnetic frame ( yoke):- The outer cylinder frame to which the main poles are fixed. it serve two purpose
a. It provide mechanically protection to the inner part of the machine and from external damage and lightining .
b. It provide lower reactance path for the magnetic flux . it is made up of cast iron.
2. Pole core and pole shoe :- The pole core and pole shoe are fixed on the yoke by bolts. These are made of thin cast steel or wrong iron lamination .Which are riveted together poles produce the magnetic flux . When the field winding is excited pole shoe is an extended part of pole . Due to its shape the pole are is enlarged and more flux can pass through the air gap to the armature.
3. Field winding :- The coils around the poles are known as field ( or exciting) coils and are connected in series with fields winding copper wire is used for the construction of fields coils when the Dc currents is passed through the field winding . it poles which produce magnetic flux.
4.Armature core:- IT is a cylindrical drum and keyed to the rotating shaft. A large no. of slots are made all over its periphery which accomodates the armature winding . Low reluctance and 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 currents losses. The air holes are also provide on the armature core for the air circulation which helps inn cooling the motors.
5. Armature winding :- The armature winding plays very important role in construction of a DC motors because the conversion of power takes place in armature winding on the basis of connection, there are Two types
There are two types of Armature winding
a. Lap winding :- In a lap winding the armature conductor and divided into a p group . All the conductor in group are connected in series and all such group are connected in parallel .For a Lap winding the number of parallel path(A) is equal to the number of poles(p)
Due to existence of a large number of parallel paths, the lap wound armature is capable of supplying l.arge load currents therefore , lap winding is used for low voltage high current DC motors.
b.Wave winding:- In wave winding , all the conductor are connected i series to form a single closed circuit . The closed circuit is tapped at various point . The two carbon brushes touch two diametrically opposite . tappings
for wave winding the number of parallel is equal to two irrespective of the no. of poles . The wave winding is usefull for high voltage low currents motors.
6. Commutator:- It is mounted on the shaft. it is made up of large no. of wedge -shape segment of hard drawn copper , insulated from each other by thin layer of Mica.
The commutator connects the rotating armature conductor to the stationary external circuit through carbon brushes. It convert alternating torque into un directional torque produce in the armature .
7. Carbon brushes :- The current is conducted from voltage sources to armature by the carbon brushes which are held against the high - grade carbon steel and are rectangular in shape.
8.Bearings:- The ball or roller bearing are fitted in the end housing . The friction between stationary and rotating part of the motors is reduced by bearing
Bearing is made up of high carbon steel as it very hard materials.
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