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

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SUMMARY

The discussion centers on the instability of asynchronous AC induction motors, particularly when overloaded, causing the rotor speed to drop below the maximum torque point. This results in the motor stalling, even if the load is subsequently reduced. Key factors include the relationship between the motor's torque and the load's torque, with constant torque loads being more likely to cause stalling. Squirrel cage motors, especially those with modern driving electronics, exhibit different behaviors compared to traditional designs, often preventing stalling under unloaded conditions.

PREREQUISITES
  • Understanding of asynchronous AC induction motor principles
  • Knowledge of torque-speed characteristics in electric motors
  • Familiarity with squirrel cage motor designs and applications
  • Basic concepts of motor control and driving electronics
NEXT STEPS
  • Research the torque-speed curve of asynchronous AC induction motors
  • Study the impact of load types on motor performance, particularly constant torque loads
  • Explore advancements in driving electronics for squirrel cage motors
  • Investigate methods to prevent stalling in induction motors under various load conditions
USEFUL FOR

Electrical engineers, motor control specialists, and anyone involved in the design or maintenance of AC induction motors will benefit from this discussion.

EVriderDK
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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 :)
 
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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.
 
I cannot find anything about this, sorry.
 
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.
 
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?
 
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