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Why Slipring Motor used in Crane

Hello Friends, in this post, we will discuss why we use slip ring motors in cranes. We will also see some important questions related to the slipring motor. So let’s start without wasting time.

Why Slipring Motor used in Crane?

The answer in just one line is in all cranes or lifts, we need a motor whose starting torque is very high.

Now some people will confuse that what is torque. So let’s understand first what is torque. But if you want to understand torque briefly, you can read this post (Click Here). There is a brief explanation of torque. So let’s take a quick revision of torque.

What is Torque in Motor?

To better explain what torque is in the motor, we are taking two conditions.

Case 1-  Suppose you have a bicycle and no one is sitting on this cycle, and now you are asked to ride this cycle, then you can easily run it by giving a pedal in the cycle with less power.

cycle torque

Here you have to apply very little force to start cycle.

Case 2- But now, if in the second case suppose that 3-4 people are now seated behind on this cycle and you are now asked to start the cycle.

So in this second case we will find that it is more difficult to start the cycle.

Now why, difficult to start the cycle in the second example? So this is happening because in the second case, we have to apply more force to start the cycle due to the sitting of 3-4 people on the cycle, which means starting high-pressure need.

So friends, in both the examples, you can understand torque practically. Here in the first case, we need to apply less pressure to start the cycle, which means we needed very little torque, but when it came to starting the cycle by sitting 3-4 people, then in that case we needed high torque. .

So friends, exactly the same thing happens with our cranes. Whenever we talk about a crane, we know that there is heavy  weight on the motor of the crane and the motor has to rotate by lifting that load.

crane slipring

So we need a motor for the crane which can run smoothly even with high load in starting, that means we need a motor whose starting torque is very high.

Friends, till now we have learned in this post that we need a motor in the crane, whose starting torque is very high. The most used motor is the squirrel cage induction motor, but its starting torque is very less, why it is less, We will understand this later.

But before that you should know that after all how is the starting torque of slip ring motor more?

Why Slipring motor starting Torque is High?

slipring motor

High torque of the slip ring motor is related to the construction and working of this motor, when you ever look at the slip ring motor, you will see that this motor looks almost similar to the squirrel cage induction motor. But friends, there is some difference between a slip ring motor and a squirrel cage motor.

Difference between Slipring and Squirrel cage motor?

Friends The main difference between Slipring and Squirrel cage motors is their rotor itself.

difference between slipring and cage

When you look at the rotor of both these motors, you will see that in our slip ring motor, winding is done on the stator as well as its rotor, and after winding on the rotor, one more main thing is connected to a rotor that is Slipring.

What is slipring and its uses?

Friends, you can see in below picture how slipring looks like in the motor.

But if we talk about its use, it works like a carbon brush.

You must have seen the carbon brush installed inside many motors, in the same way, slipring is also applied on the rotor of the motor. With the help of this slipring, we can connect the motor’s rotor with the resistance box kept outside.

On the other hand, if we talk about a squirrel cage motor, then winding is done on the rotor, but the structure of its rotor is simple.

The winding on the squirrel cage rotor is done with the help of a conductor bar, which you can see in the picture. Apart from this, there is no other winding on this rotor, due to this squirrel cage rotor is very simple.

But friends, now let’s talk about a very important question. Why are we connecting the winding of its rotor to the resistance box?

What is the use of Resistance Box in Slipring Motor?

What is the use of a resistance box in a slipring motor? Whole working of this motor is very easy. For this, you just have to always remember one simple thing.

That is, whenever we increase the resistance of the rotor of a motor, that means, if we add a rotor with more resistance , then due to this the current value of the motor decreases, and due to the decrease of this current, and there is a very high torque is produced.

Inside the slip ring motor, we put a slip ring on the rotor, and the wire that comes out from the slipring, we connect it to the resistance box with the help of a contactor.

After this, whenever we need more torque from the motor, at that time we add extra resistance on the rotor with the help of slipring. Due to which, the current of the motor decreases, and we get more torque from the motor.

So friends, till now, we have understood that what is slipring motor, how it works, and what is the difference between a squirrel cage and a slipring motor. But now, after this, we will talk on one last question, can we use squirrel cage motor on crane?

Can we use Squirrel cage Motor on Crane?

The answer to this question is in simple words yes, we can use Squirrel cage motor in a crane. But now, after hearing this answer, most of the people will think that if we can use a squirrel cage motor, then why are we using crane slip ring motor?

So friends, here you should know one thing, that if we ever want to use squirrel cage motor in crane, then at that time we have to take high starting torque from squirrel cage motor. After all, the question comes that how can we get more torque from the squirrel cage motor?

So, friends, you have to connect V.F.D with this motor for this, which means that the variable frequency drive will have to be added.

you can read in detail about VFD (Click Here)

If you want to see it practically, then you can see its use inside the train.

Whenever we have to start a train, a lot of torque is required, and we easily take this torque requirement from our squirrel cage motor. Because inside the train we are using V.F.D.

But when we talk about the industry and in high torque places like inside cranes, there we always use slipring motor, not squirrel cage motor. Because to get more torque from the squirrel cage motor, we have to install VFD, and when we look at the price of VFD Drive, then it is very expensive. So, for this reason, only slipring motors are used in the industry where need for high torque.

We hope that you understand. if still any doubt or question remains then feel free to ask in comment section or you can ask this question on Instagram (Click Here).

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