# Asynchronous motors - the heat of the rotor

• fawk3s
In summary, the efficiency of an asynchronous motor is affected by the resistance of the rotor, with lower resistance resulting in higher mechanical work output. However, it is important to also consider other factors such as copper and iron losses in the motor. Comparing two motors with different rotor resistances, the more efficient motor will have lower losses to heat and can operate at a higher power.

#### fawk3s

So I was reading about asynchronous motors, and it seems the motor works better when the resistance of the rotor is smaller. This is fairly obvious, because the smaller the resistance, the bigger the inductive currents and therefore more mechanical force is applied on the rotor, thus its doing more mechanical work (leaving out the frequency of the current at the moment for simplification).
Now as I started thinking about it in more depth, I stumbled upon this question:

If the resistance of the rotor of one motor is say 2x smaller than the resistance of the rotor of another motor, and therefore the first motor (with the smaller-resistance-rotor) is able to do say 2x more mechanical work in a time unit, does the rotor of the first motor also do more work via heating than the second?
Because of P=V*I=I^2*R

fawk3s

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To good approximation you can lump all the losses due to source resistance, lead resistance, winding resistance and core loose together as a single resistance in series with the load. The load is an effective variable resistance. This should make your comparative analysis of two motors fairly simple.

When considering the total losses to heat, a 80% efficient motor will have double the losses to heat of a 90% efficient motor. Assuming the same temperature limit and rate of heat dissipation, the 90% efficient motor can operate at twice the power of the 80% efficient motor.

I would respond by saying that the relationship between rotor resistance and mechanical work in asynchronous motors is indeed important to consider. However, it is not the only factor that affects the amount of heat generated in the rotor.

In an asynchronous motor, the heat generated in the rotor is a result of the losses in the motor, including copper losses (caused by the resistance of the rotor and stator windings) and iron losses (caused by the magnetic properties of the motor's core). So while a lower rotor resistance may result in more mechanical work being done, it does not necessarily mean that the rotor will also generate more heat.

Other factors that can affect the amount of heat generated in the rotor include the design and materials used in the motor, the operating conditions (such as speed and load), and the efficiency of the motor. So while a lower rotor resistance may contribute to more heat being generated, it is not the only determining factor.

It is also important to note that the heat generated in the rotor is not necessarily a bad thing. In fact, some amount of heat is necessary for the motor to function properly. However, excessive heat can lead to reduced efficiency and potentially damage to the motor.

In conclusion, while a lower rotor resistance may result in more mechanical work being done, it does not necessarily mean that the rotor will also generate more heat. The overall design and operating conditions of the motor also play a significant role in determining the amount of heat generated in the rotor.

## What is an asynchronous motor?

An asynchronous motor is a type of electric motor that operates by using an alternating current (AC) power supply. It is commonly used in industrial and commercial applications due to its simple design, low cost, and reliable performance.

## How does an asynchronous motor work?

An asynchronous motor consists of two main parts: a stationary stator and a rotating rotor. The stator has a set of windings that produce a rotating magnetic field when connected to an AC power source. The rotor, which is made of conducting material, is placed inside the stator and is free to rotate. As the magnetic field of the stator rotates, it induces an electric current in the rotor, causing it to turn and drive the motor.

## Why does the rotor of an asynchronous motor heat up?

The rotor of an asynchronous motor heats up due to the flow of electric current through its conducting material. This current is generated by the interaction between the rotating magnetic field of the stator and the stationary rotor. The resistance of the rotor material causes it to heat up as a result of this current flow.

## What are the consequences of excessive heat in the rotor of an asynchronous motor?

Excessive heat in the rotor of an asynchronous motor can lead to several consequences, including decreased efficiency, reduced motor life, and even motor failure. The heat can cause the rotor material to expand, leading to mechanical stress and potential damage. Overheating can also affect the insulation and cause short circuits, leading to motor failure.

## How can the heat in the rotor of an asynchronous motor be managed?

The heat in the rotor of an asynchronous motor can be managed by proper design and maintenance. This includes using materials with low resistance and high heat tolerance, ensuring proper ventilation and cooling of the motor, and monitoring the motor's temperature during operation. Regular maintenance and timely repairs can also help prevent excessive heat buildup in the rotor and prolong the motor's lifespan.