Single phase induction motor Torque under increased frequency and Same Current

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Discussion Overview

The discussion centers on the torque and power characteristics of a single-phase induction motor when the supply frequency is increased while maintaining the same supply current. Participants explore the implications of these changes on motor performance, including theoretical considerations and practical limitations.

Discussion Character

  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant questions the torque of the induction motor when the supply frequency is increased to 500 Hz while keeping the current constant at 10 Amperes, suggesting it might be 10 times the original torque.
  • Another participant argues that maintaining the same current results in the same torque, regardless of frequency, and notes that increasing frequency leads to a proportional increase in RPM and thus power, but requires a corresponding increase in voltage.
  • A later reply emphasizes that in an idealized scenario without friction or losses, torque does not increase with frequency if current remains constant.
  • One participant explains that torque is related to the product of current and magnetic flux (I*ø), indicating that higher frequency reduces flux, necessitating higher voltage to maintain it.
  • Another participant suggests using simulation software to explore different scenarios for motor behavior, mentioning various modeling approaches including Finite Element Method (FEM) and analytical models.

Areas of Agreement / Disagreement

Participants express differing views on the relationship between torque and frequency under constant current conditions. There is no consensus on whether torque increases or remains the same with increased frequency.

Contextual Notes

Participants mention idealized conditions such as the absence of friction and eddy current losses, as well as practical concerns regarding motor design limitations at higher speeds.

StoyanNikolov
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TL;DR
Single phase induction motor Torque under increased frequency and Same/Constant current.
Hi ,

Consider Single phase induction motor.

What will be torque of induction motor, if we increase supply frequency 10 times, if the motor uses same supply current.

Let's say Torque (Supply frequency 50 Hz, Supply current 10 Amperes ) = N

What is Torque (Supply frequency 500 Hz, Supply current 10 Amps) = ?

Will it be 10*N ?
------------------------------------------
Also what will be the Output Power?

Let's say Power (Supply frequency 50 Hz, Supply current 10 Amperes ) = NWhat is Power(Supply frequency 500 Hz, Supply current 10 Amps) = ?
Thank you.
 
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Same current = same torque.
Ten times frequency = 10 X RPM.
10 X RPM * same torque = 10 X power.

But you will need 10 X the voltage to get that much current at that frequency. The rotor and bearings are normally not designed for that speed, so it could self destruct due to rotor hitting stator at critical speed or bearing failure or rotor exploding or stator windings shorting or cooling fan exploding or ....
 
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Thank you for Reply. It is idealised situation .
No friction.
No Eddy current losses.

So Torque doesn't increase if we increase supply frequency, when motor uses same current.
 
The torque is related to I*ø . With higher frequency, the flux will be reduced and you have to maintain it with the voltage .
Simple simulation can help to try different scenarios. Is there any easy to use simulator for electrical motors?
 
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alivakilian said:
The torque is related to I*ø . With higher frequency, the flux will be reduced and you have to maintain it with the voltage .
Simple simulation can help to try different scenarios. Is there any easy to use simulator for electrical motors?
There are a lots of software you can use to model motors. Some of them using Finite Element Method and some just use the analytical models. Of course the analytical models are faster, but FEM results are more accurate and trustable. According to my own experience, I used EMWorks software. I think it has both simulation models and you can Choose to use FEM or not. search them on net and you will find useful videos as tutorials to start.
 

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