Single phase induction motor Torque under increased frequency and Same/Constant current.

[StoyanElectroTech]

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 ) = N


What is Power(Supply frequency 500 Hz, Supply current 10 Amps) = ?
Thank you.

 

[schmitt trigger]

Is this homework or technical curiosity?
An induction motor will never, never, never run at 10X the base frequency. Either the centrifugal forces or the core losses will destroy it long before you reach that speed.
To answer your question in a theoretical matter, I need to know whether this is homework or not.

 

[StoyanElectroTech]

Hi and THANK YOU. It is curiosity in ideal situation.

 

[rjenkinsgb]

Power is proportional to torque x speed.
Ten times speed with the same torque would be ten times power.

It would take 10x current to maintain the same torque.

 

[Diver300]

Power is proportional to torque x speed.
Ten times speed with the same torque would be ten times power.

It would take 10x current to maintain the same torque.

I think that it would need about the same current to get the same torque. At 10x the frequency and 10x the speed, it would need about 10X the voltage. Obviously, all sorts of other effects will actually come in at 10x the speed and frequency, so it wouldn't work quite like that. The fan would take lots of power, the eddy current losses would be terrible and the rotor would probably burst.

Generally on a motor,
Torque is approximately proportional to current.
Speed is approximately proportional to voltage

Additionally, on ac motors, speed is approximately proportional to the frequency.

Inverters generally keep the voltage and frequency in proportion. That is something that I found and described here:-
https://www.electro-tech-online.com...e-phase-motor-from-single-phase-mains.161572/

 

[StoyanElectroTech]

Thank you for the answers.
It is of course ideal motor situation .
No Eddy current losses .

Ten times higher frequency.
Same supply current.

What will be the Output Torque?
What will be Output Power?

Let's consider squirell cage induction motor
Single phase shaded pole.

https://www.google.com/url?sa=t&source=web&rct=j&opi=89978449&url=https://circuitglobe.com/shaded-pole-induction-motor.html&ved=2ahUKEwjP9vXWtvSDAxXWS_EDHemkCscQFnoECBEQAQ&usg=AOvVaw3NtCHepmiGP2I7mDGPzv9X

 

[schmitt trigger]

AC INDUCTION motors (not the AC SYNCHRONOUS) are constant V/f ratio devices. If you increase the frequency without increasing the voltage, the rotor slip will increase and the torque will drop like a rock.
You would have to increase the input voltage 10 times, meaning that the applied voltage would be 2.3 kilovolts.
Thus, in addition to the core overheating, the bearings overheating, the 10X centrifugal forces pulling the rotor apart, you would have the insulation arcing all over the place!

 

[StoyanElectroTech]

AC INDUCTION motors (not the AC SYNCHRONOUS) are constant V/f ratio devices. If you increase the frequency without increasing the voltage, the rotor slip will increase and the torque will drop like a rock.
You would have to increase the input voltage 10 times, meaning that the applied voltage would be 2.3 kilovolts.
Thus, in addition to the core overheating, the bearings overheating, the 10X centrifugal forces pulling the rotor apart, you would have the insulation arcing all over the place!

lers consider ideal situation.
No eddy currents
Perfectly insulated conductor windings
No friction

 

[StoyanElectroTech]

Increasing the frequency 10 times while keep same input current
T =
P=

 

[Diver300]

lets consider ideal situation.
No eddy currents
Perfectly insulated conductor windings
No friction
Increasing the frequency 10 times while keep same input current
T =
P=

Torque and power are both raised by 10 times.

Of course, to get the current and torque to be 10 times as big, you have to adjust the load as well as the input frequency, and the input voltage will need to be 10 times as much as well.

 

[StoyanElectroTech]

Torque and power are both raised by 10 times.

Of course, to get the current and torque to be 10 times as big, you have to adjust the load as well as the input frequency, and the input voltage will need to be 10 times as much as well.

Thank you.
P=T*w
P = 10*T*10*w=100*T*w

 

[Diver300]

Thank you.
P=T*w
P = 10*T*10*w=100*T*w

Torque and power are both raised by 10 times.

Of course, to get the current and torque to be 10 times as big, you have to adjust the load as well as the input frequency, and the input voltage will need to be 10 times as much as well.

I now think I got that wrong. I should have said that speed, frequency, voltage and power are all raised by 10 times.

The torque will remain much the same, because it is approximately proportional to current, and the current should remain the same.

 

[Tony Stewart]

We are talking available torque since actual torque depends on a non linear load to decrease with increasing voltage and increasing BEMF with RPM in order to keep current constant. At some point there will be 0 torque and it can't go any faster due to rising EC and thermal losses. Take a look at VFD dynamics for current and synchronous voltage control with variable loads.