Ok, but WHY does the asynchronous AC induction motor have an unstable zone?

In summary, an asynchronous induction motor can become unstable and stall if it is overloaded and the rotor speed drops below the maximum torque point. This is because the motor's torque decreases faster than the load's torque. However, newer squirrel cage motors are designed to avoid stalling and can even continue running when unloaded. The use of driving electronics also plays a role in the stability of the motor. Despite this, some motors, such as fans, still use bare squirrel cage motors. When a motor stalls, the only solution is to turn it off and on again, even if it becomes unloaded. The cause of stalling may be due to the rotor becoming over magnetized.
  • #1
EVriderDK
56
0
I have been tought several times that if an asynchronous induction motor is overloaded, so that the rotor speed goes below where the maximum torque point is, the motor will become unstable, and simply stall, even if you unload it.

Why does it do that?

fx. here: http://youtu.be/ze8LY4yq9Wk?t=38m20s

Thanks in advance :)
 
Engineering news on Phys.org
  • #2
Do a search on this forum about induction motors. There have been a number of threads that discuss the operation in depth. I think it would help you.
 
  • #3
I cannot find anything about this, sorry.
 
  • #4
It is unstable if the motor's torque decreases with the lower rotation speed faster than the load's torque decreases.

A load with constant torque can let the motor stall, an fan for instance never does.

Squirrel cage motors born after you and I won't stay stalled if unloaded. Better, they can be built so that their torque doesn't decrease at low speed.

These days, squirrel cage motors tend to have a driving electronics which changes everything. Bare squirrel cages still exist for fans. And since driving electronics are common, squirrel cage motors replace most other motors.
 
  • #5
Yes, i get that, but my teacher said, that if it stall, there is nothing else to do, than turning it off and on again, also if it gets unloaded. I cannot understand how it can stall with the stators magnetic field still fluxing around?!

Is it because the rotor gets over magnetized or something like that?
 
Last edited:

1. What is an asynchronous AC induction motor?

An asynchronous AC induction motor is a type of electric motor that uses alternating current (AC) to induce a magnetic field in the rotor, causing it to rotate. It is commonly used in industrial and household applications due to its simple design and low maintenance requirements.

2. How does an asynchronous AC induction motor work?

An asynchronous AC induction motor works by using the rotating magnetic field of the stator to induce currents in the rotor, which in turn creates a torque and causes the rotor to rotate. The speed of the rotor is slightly less than the speed of the rotating magnetic field, hence the term "asynchronous".

3. What is the unstable zone in an asynchronous AC induction motor?

The unstable zone in an asynchronous AC induction motor refers to a range of speeds where the motor experiences instability and can potentially stall or trip. This usually occurs at low speeds, close to the synchronous speed of the motor. It is a limitation of the motor design and can cause issues in certain applications.

4. Why does the asynchronous AC induction motor have an unstable zone?

The asynchronous AC induction motor has an unstable zone due to its design, which relies on the difference in speed between the rotating magnetic field and the rotor to create torque. At low speeds, this difference decreases, resulting in a weaker torque and potential instability. Additionally, factors such as load variations and power supply fluctuations can also contribute to the unstable zone.

5. How can the unstable zone in an asynchronous AC induction motor be managed?

The unstable zone in an asynchronous AC induction motor can be managed by using speed control techniques, such as variable frequency drives, to keep the motor operating within a stable speed range. Proper motor sizing and load balancing can also help to reduce the risk of instability. In some cases, a different type of motor, such as a synchronous motor, may be more suitable for the application to avoid the unstable zone altogether.

Similar threads

Why can't a 2 pole ac induction motor run a 6 pole induction generator
    • General Engineering
Replies
4
Views
2K
DC motors and Induction motor: What does "no load conditions" mean?
    • Engineering and Comp Sci Homework Help
Replies
10
Views
2K
Eddy currents in case of synchronous and asynchronous motors
    • Electrical Engineering
Replies
14
Views
3K
Increasing induction motor frequency
    • Electrical Engineering
Replies
9
Views
722
Engineering Calculating Power Losses in an AC Induction Motor
    • Engineering and Comp Sci Homework Help
Replies
7
Views
2K
Can an Induction Motor be Used as a Generator for a Micro-Hydro Power System?
    • General Engineering
Replies
2
Views
4K
Design choices for running an Electric train (and network)?
    • Electrical Engineering
Replies
6
Views
1K
Electric Trains (in general)
    • Electrical Engineering
Replies
11
Views
1K
Poles of AC Induction Motors
    • Electrical Engineering
Replies
2
Views
1K
Asynchronous Motor Starting: Understanding the Initial Current Flow
    • Electrical Engineering
Replies
12
Views
3K

Hot Threads

Recent Insights

Back
Top