Why these strips are made only on the induction motors?

Guys have you ever noticed that these kinds of strips are only built over frames of the induction motors. However, if we see a DC motor of the same rating, we didn't find these strips.

strips are provide to increase surface area of induction motor to imporve cooling

High rating and low rating DC motor

Let me tell you the reason. the first thing is that the stator of "induction motor". gets more heated as compared to the stator of "DC motor".

stator and winding and stator

As we know we give "AC current" to the stator winding of "induction motor". whether it is a "single phase" or "three Phase". And ac current makes "Changing Magnetic Field"

Any metal comes in the vicinity of this "Changing Magnetic Field. Like, the "winding" of the rotor, an EMF get induced in that. and due to the closed circuit, AC current starts flowing in that.
when three phase supply given to the stator or induction motor it creates changing magnetic field that is rotating field

This also applies to the "stator core" and the "frame". And, cyclones of electric current get produced in both. this cause excessive loss of energy in form of heat and this current is known as "Eddy Current".

flow of eddy current in motor core and frame and produce heat

To reduce this current as much as possible, we make the "stator core" from thin layers so that the "Effective Resistance" of the core is increased. But it is not possible to make the frame in layers, it should be strong. "Eddy Current" does not contribute to the function of the motor. Only, It does energy loss in the form of heat.

laminated core of induction motor three phase or single phase

That's why to dissipate this heat, the strips are placed on the frame of induction motor, this increases the surface area of the motor. and the temperature of the motor remains in the limit. so that insulation of motor doesn't get melt and not cause "short circuit" between turns of the "winding".
strips are provide to increase surface area of induction motor to imporve cooling

Remember that in the "stator winding" of DC motors we give Direct Current, which produces stationary magnetic poles. until the magnetic field associated with the "stator Core" and the "frame" does not changes, no EMF can be induced in them. So, there will be no such "Eddy Currents".  .And, no such production of heat in the stator Core and the "frame" of DC motor.

Dc motor with and without field excitation

That's why the "Pole shoes" of DC motors are made solid, they do not need to "laminate" means no need to make them in layers, and there is no need to do this type of special cooling arrangement in its frame.
DC motor solid pole shoes or stator poles with no winding
But in its rotor Eddy current will produce. Even if the magnetic field of the stator is stationary but the rotor rotates then the rotor will feel like a magnetic field change. Therefore it is necessary to laminate the rotor of the DC motor.
to reduce eddy current rotor of dc motor is laminated

in the winding where we give AC supply or generate, the core must be laminated. Such as in a transformer, in Choke of Tubelight. The stator core of "alternator" is often laminated as AC voltage is produced in its stator winding. whereas the rotor consists of the solid core because it is energized by a DC supply to produce fixed poles.
Hope, now you have understood why these stripes are built only over the frames of induction motors.

Than You

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