Why Rotor Slots are Skewed?

Why Rotor Slots are Skewed

If you are from electrical engineering, you know that many questions about motors are asked in exams and interviews.

But friends, one such question that most people ignore is, Why Are Rotor Bars Skewed in An Induction Motor? So today, we will give you the answer to this question in easy words.

So let’s first know what are slots and why they are made. Then we will also know Why Rotor Slots Are Skewed?

What is the Slot?

Friends, slots are made in both rotor and stator. As you can see in the photo below, space is created in this way to keep the windings inside our rotor and stator.

rotor-slot

Friends, the space made for keep winding, this is called slot. Mean we keep the winding inside the slot. But friends, now this question must be coming to your mind that there is a winding in the stator, so slots are made. But inside the rotor, we do not have any winding, so why are slots made in it?

Why are Slots made on Rotor?

Friends, you always have to remember that winding is also done inside the rotor, but in the rotor, we do not winding with copper wire. We do winding with strips of copper.

rotor-bar

You can easily understand by looking below how our original rotor looks and how slots are made in it. Inside these slots, we place a copper strip or bar. Here we keep the copper bar in the slot and sort them instead of winding them. Due to this, it acts like a winding.rotor-slots

So, friends, one thing has become clear to you from here: what are the rotor slots, and why are they made? So let us now understand our main question why are rotor slots skewed?

Why are Rotor Slots Skewed?

Friends, whenever this question is asked in the interview, you first have to tell one line that not only in squirrel cage motor the rotor slots Skewed but in slip ring motor rotor slots are also skewed.

slip-ring-rotor

The next question will be asked what the difference is between a slip-ring rotor and a squirrel-cage rotor; then, you can say that inside the slip ring, we make winding in the rotor slot, which is not short. Whereas inside the squirrel cage, we keep the copper bar inside the slot, which is intertwined.

Friends, now you have to say there are four main reasons behind Rotor Slots Skewed. Let’s understand one by one:-

  1. Increased starting torque
  2. Prevents Cogging
  3. Prevents Crawling
  4. Humming Sound

Increased starting torque: The starting torque of our motor increases due to the Skewed of the rotor slot. Torque means the pressure exerted on our motor due to rotating. So by keeping the slot Skewed, there is more force applied to our motor, so we can start the motor by adding more load.

RPM Torque difference in motor

Now the question must be coming into everyone’s mind how is the torque increasing by keeping the slot Skewed? So friends, you have to keep in mind that when our current decreases, our torque increases.

When we keep the slot of the rotor Skewed, the length of the copper strip increases; when the length of something increases, its resistance increases.

When resistance is increased, then less current will flow. So current is decreased, and torque will increase.

Mean with slot Skewed resistance is increased and current decreased due to which torque is increased.

Prevents Cogging: Skewed slot in the rotor helps to avoid cogging. Cogging is a type of magnetic locking in which the rotor gets jammed or stops rotating. When the slots of the rotor and the slots of the stator become equal, then the condition of magnetic lock arises.

Cogging-in-motor

For example, our rotor has five slots, and the stator also has five slots, so at that time the magnetic flux produced by our stator is canceled by the magnetic flux produced by the rotor and our rotor is locked. We call this condition cogging.

So friends, you have to keep in mind one thing that slot Skewed helps to avoid cogging.

Prevents Crawling: Friends, you must know that our motor is non-linear load. A non-linear load always produces harmonics. Harmonic is our kind of electrical disturbance, due to which the speed of our motor decreases. If our motor is running at 1000 RPM, then the speed of the motor becomes 300, 400 RPM due to harmonic.

induction-motors-harmonics

Therefore, Skewed slots placed so that all the harmonics produced in the motor can be eliminated.

Humming Sound: There is also an advantage when the slot of the rotor is skewed that the humming sound produced due to the rotation of the motor is also reduced.


So friends in this post we have understood that what is slot and and why slots are placed Skewed. If any question left then you can comment out below or you can send question to us on Instagram Electrical Dost.”

If you like to see video of electrical then you can visit our channel Electrical Dost.” 

Thank You 🙂

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Aayush Sharma is an Assistant Engineer in a Semi-Government Company and Owner of "Engineering Dost" and the Electrical Dost YouTube Channel. He Provides you Engineering inquiry and support of engineering market facts with Practical experience.

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