Question

Describe how a DC motor works. Be sure to list the parts and describe the function for each.

Answer 1

Working Principle Of A DC Motor:-

A motor is an electrical machine which converts electrical energy into mechanical energy. The principle of working of a DC motor is that "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 it's magnitude is given by F = BIL. Where, B = magnetic flux density, I = current and L = length of the conductor within the magnetic field.

Construction of Dc motor nearly looks like the construction of Dc generator, originally when the Dc machine starts working we can’t identify whether it’s a Dc generator or motor, briefly Dc motor consists of:

• Stator: it’s the stationary part containing the field winding and receives the supply.
• Rotor: which is the rotating part.

Construction of dc motor in detail, there is a yoke (Magnetic frame), pole core and pole shoes, the armature core, armature winding (conductor), commutator, and brushes and bearings. Each part of those has its identity and great importance, advantage and sometimes problems, now we will separately explain each part.

• The yoke of DC motor:

The yoke is the outer cover (frame) of the machine, it’s made of cast iron in small machines where cheapness is an important consideration and in large machines, it’s made of cast, silicon, or rolled steel to provide high permeability.

• Pole shoes and pole core of DC Motor:

Pole core is a solid piece made of cast iron or cast steel build of thin laminations which are perfect to reduce power losses due to eddy current.

• Field Winding of DC Motor:

It’s usually a copper conductor wound around pole core with a definite direction, We usually connect it in series and when the current passes through it the poles electro magnetized and produce the necessary flux.

We must make the Field winding of conducting materials like aluminum or copper because it carries the produced current.

• Armature core of DC Motor:

Armature core is a cylindrical shape mounted to the shaft and rotates between the field poles and keyed to the machine shaft it uses high permeability low reluctance materials like cast iron or cast steel, there are also laminations coated with a thin film to reduce losses due to eddy current, laminations also provide mechanical security to the armature winding.

There is a large number of slots in the armature core periphery and we place in those slots.

• Armature winding of Dc motor:

Armature winding is the interconnection of armature conductors.

And we can make those windings of conducting materials like copper.

When we use a prime mover to rotate the armature a magnetic flux and voltage induced in it.

It’s important because it carries the current supplied to the machine.

• The commutator of DC Motor:

The commutator is a cylindrical mechanical rectifier made of edge shaped copper segments insulated from each other by a thin layer of mica those segments are made of hard drawncopper.

• Brushes of DC Motor:

Brushes are carbon or graphite rectangular shapes inspected regularly because they wear with time, they rest on the surface of the commutator.

We use brushes to collect the current from the commutator and apply it to the external load; in another meaning, they ensure the electrical connection between the rotating commutator and the stationary external load circuit.

Since we are talking about brushes you should know that there are brushless Dc motors that we can use in high-speed applications.

And multiple machines have the number of brushes as the same of the number of the poles.

• Bearings of Dc motor:

Ball bearings are the most popular because they are more reliable so they are the perfect on heavy duty machines.