construction details of a dc machine

Construction details of a dc machine

Parts of dc machine

•       Yoke

•       Pole core and pole shoe

•       field winding

•       Armature core

•       Armature winding

•       Commutator

•       Brushes and bearings

Yoke:

–      It is the outermost cover of the M/C, provides mechanical Support for poles

–      It also provide protection to whole machine from dust, moisture etc.

–      It also carries magnetic flux produced by the poles

–      Yoke is also called as frame.

–      For small M/C yoke is made of cast iron.

–      For large M/C it is made of cast steel or rolled steel.

Pole core and Pole shoe:

•       Pole of a generator is an electromagnet.

•       Each pole is divided into two parts

      (i)            Pole core

    (ii)            Pole shoe

Pole core: carries field winding which is necessary to produce flux.

Pole shoe: it is a extended part of pole core, it spreads the flux in air gap.

Materials used:

–      Pole core is made of cast iron or cast steel.

–      The laminations is done to reduce eddy current losses.

Field winding:

•       It is wound around pole core and called as field coil

•       it is connected in series to from field winding

•       When Current is passed through field winding it electro magnetize the poles which produce necessary flux.

•       Made up of aluminium or copper.

Armature:

•       Consists of two parts

      (i)            Armature core

    (ii)            Armature winding

Armature core:

•        It is cylindrical in shape mounted on the shaft and consists of slots on its periphery and air ducts to permit air flow through armature which serves cooling purpose.

•       It provides house for armature winding.

Materials used:

•       Made up of cast iron or cast steel.

•       It has laminated construction to reduce eddy current losses as low as possible.

Armature winding:

•       It is placed in armature slots and generation of e.m.f takes place in armature winding in case of generator.

Two types (i) Lap winding  (ii) wave winding.

Materials used:

•       Made up of conducting materials like copper or aluminium.

Brushes and Bearings:

Brushes:

•       Brushes collect the current from commutator and apply it to external load.

•       They are rectangular in shape and rest ion the commutator segments against spring tension.

Materials used:

•       Brushes are made of carbon or graphite

Commutator:

·         It is cylindrical in shape, made of copper and it has several segments.

·         It converts the induced ac emf into dc emf.

Bearings:

•       Bearings are fitted inside the cover to provide free and smooth rotation to the armature.

•       The types of bearings are ball bearing and roller bearing.