What is a DC Machine : Construction & Its Working

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What is a DC Machine Construction & Its Working
What is a DC Machine Construction & Its Working

Construction of DC Machines (Motor & Generator) With Diagrams

Construction of DC Machine

A Direct Current (DC) machine is an energy conversion device. It converts electrical energy to mechanical while working as a motor and the mechanical energy to electrical energy while working as the generator. Hence, it is known as electromechanical energy conversion device. It consists of stator and rotor. The stator is the assembly of main parts like the yoke, main poles, pole shoe, inter pole windings etc., and the rotor is the assembly of the armature, armature winding, commutator fan etc.

DC Machines

Major Parts of DC Machine Construction

Yoke

The yoke is the outer cover of the machine supporting and protecting the internal parts. It is made of low reluctance ’ material like silicon steel or cast iron, Since, it has to carry the magnetic flux i.e., to provide the closed path for the flux produced through the poles.

Pole Core and Pole Shoe

Pole core is generally a solid material and pole shoe is a laminated one in small machines, but the pole shoe and pole core both are laminated made of annealed steel in modern days. The purpose of the pole core is to provide flux and to support the field windings, Whereas the pole shoe is stretched so as to provide uniform air gap along the armature core and also to provide uniform flux distribution in the air gap.

Brush and Brush Holders

Brushes are the structures placed on the rotating commutator through which the unidirectional current is to be collected. Generally, it is made of carbon, which can give smooth surface to the contacts so as to reduce the spark and wear and tear of the commutator bars. These are fixed to the stator core (yoke) by means of brush holders.

Field Windings

The field windings are wound initially on a wooden former and then installed into the pole cOre. These are generally made of low resistivity materials like copper or aluminum. There are two ways of connecting the field winding to the armature in case of the self-excited machine. They can be connected in series or shunt. If it is connected in series less numbered turns with larger cross-sectional conductors are used. If it is connected in shunt, the winding would be of large turns, whose cross-section is less, so as to withstand for the whole supply voltage.

 

 

Interpoles

These are the pole structures generally smaller than main poles and is placed in between the main poles. These windings of the inter poles are of less turns since it is connected in series with armature windings. The main purpose of these inter poles is to reduce the armature reaction, thereby reducing the sparks at the brush contacts. The polarity of the inter pole is made same as that of the main pole ahead of it in the direction of rotation.

Rotor

 

The rotor is generally rotating part which carries the armature, armature windings and the commutator on the same shaft. The armature core is made of laminated silicon steel. The main purpose is to hold the armature windings and to provide the low reluctance path for the flux.


Commutator Construction In DC Machines

The commutator helps in converting this alternating emf into direct current emf. This is, therefore, also known as the mechanical converter.

WORKING OF A DC MACHINE

As we said earlier, Construction wise both DC motor and DC Generator are same but working principle of both are very different.

WORKING OF DC MOTOR

DC Motor converts the Electrical energy (in DC) into Mechanical Energy. Working of DC Motor is based upon the fact that, when a current carrying conductor is placed in a magnetic field, then it experiences a mechanical force whose direction is given by “Fleming’s Left Hand Rule” and magnitude of that force is given by:

F = B * I *L

where,  F = Force Experienced by the conductor.

            B = Flux Density

            I = Magnitude of Current carried by conductor

            L = Length of Conductor

WORKING OF DC GENERATOR

DC Generator converts the Mechanical Energy into Electrical Energy (in DC). Its working principle is Faraday’s Law of Electromagnetic Induction which states that, whenever a conductor is placed in a varying magnetic field (or conductor is moved in magnetic field), then an emf is induced in it. If the circuit of the conductor is closed, then current also starts flowing through it. Direction of the Induced Current can be determined by Fleming’s Right Hand Rule.

Armature Windings In DC Machines

The windings placed in the armature is called the armature windings and is generally connected in two ways,
(i) Lap windings
(ii) Wave windings.
Lap windings are preferred for higher currents and low voltage and wave windings are preferred for higher voltages and lower currents.

READ HERE  How A DC Motor Works?

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