Formula for new number of turns whit new power

[pontussweden]

Hello,

Some of you may be familiar whit the formula for calculating the new numbers of turns when the voltage or the frequency change

ns*u2/u1*f1/f2=ns2

ns = numbers of turns (start)
u2 = new voltage
u1 = voltage
f1 = Frequency
f2 = New Frequency.

But do anyone here knows he formula if you also want to concider to change the power.
I know that for exampel if you decrease the power the new number of turns must increase.
I have a application, but i dont have the formula.

Please share

Best regards

 

[ScottyUK]

Substitute the secondary volatge term for one derived from secondary power.

 

[pontussweden]

Thanks for the answer!

Do you think you can put it in a formula ?

 

[electricpete]

You didn't really describe the application or what it is that you want to "maintain" when you change these other variables.
If you want to keep flux density constant, the keep the quantity u/(n*f) constant.

=====================================
(2B)+(2B)' ?

 

[electricpete]

Now I see you mentioned change of power. I don't understand that question

=====================================
(2B)+(2B)' ?

 

[pontussweden]

Hum if i start over.

Say you have a motor winded for 400 D 50 Hz rated 75kW whit 20 turns, if i want to make a new winding for 360 D 50 Hz whit the same power, then i need to take 20 * 360/400 = 18 Turns, 18 turns will my new winding have to fit the new voltage.

But i cant figure out how to calculate the new numbers of turns if the power also change.

 

[waross]

The power of a motor depends in part on the strength of the magnetic field. Induction motors are capable of outputting more than rated power but if the load exceeds the motor power rating by much, the motor will overheat.
There are a few things you can do to achieve incremental increases in power.
1> Raise the voltage. If you drop the voltage the power will drop.
2> If there is space, wind the motor with heavier gauge wire to allow more current with the same heat developed.
3> Wind the motor with a higher temperature rated wire so the current can be increased and the motor allowed to run hotter.
4> Add more cooling.
Be aware that the more load is applied to a motor, the further back on the speed/torque curve it will operate and the more slip there will be.
There is a limit to the magnetic field strength. Motors are designed to run close to magnetic saturation. This is a characteristic of the stator and rotor iron and can't be changed by changing the windings. You can't use much more than 110% of rated voltage before saturation becomes an issue.
You may use a VFD and run the motor at a higher voltage and frequency. At double voltage and double frequency you have double the HP.

Bill
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"Why not the best?"
Jimmy Carter