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low power factor in submersible induction 3 phase motor


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#1 vanraj s chawda

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Posted 28 May 2006 - 10:05 AM

hey

I am new member and facing one probelm in my product

achiving the low power factor in 5.5 kW and 7.5 kW submersible induction 2 pole motor.

in my view whether , we should increase turns per coil to reduce the current ,it will lead higher power factor

OR what changes to be done in design

Power factor for 7.5 hp is 0.73 and 10 hp is 0.66 , i want to increase the PF to 0.82

regards

vanraj


#2 marke

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Posted 28 May 2006 - 07:00 PM

Hello vanraj s chawda

Welcome to the forum.

The lower power factor is predominantly due to the high magnetising current associated with submersible pump designs.

To reduce the magnetising current, you need to reduce the flux in the iron. This will reduce the torque output from that motor and effectively reduce its rating.
The design is a compromise between cost and performance.
More iron -> higher cost and larger size but lower flux density, lower losses, and improved power factor.

The maximum operating flux density of a given frame is related to the heat generated and the ability of that frame to get rid of the heat.
Small motors have a high surface area to volume ratio and therefore have a higher ability to dissipated losses per KW rating. This enables designers to operate the motor at a higher flux density and therefore pack a higher KW rating into a smaller frame. As the frame size increases, the surface area to volume ratio gets worse and the losses must be reduced. The flux density is reduced to reduce the iron losses.

Submersible motors have a much higher cooling efficiency and so they can operate at a much higher flux density in the iron, reducing the frame size even further.

Increasing the turns per coil will reduce the flux density, reduce the iron loss, increase the copper loss, increase the power factor but will reduce the maximum torque output from that frame.

Best regards,

#3 Tua

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Posted 14 June 2006 - 06:54 AM

Hello vanraj s chawda!
Why do you want to increase PF?
Do you really need it?
You can add some capacitors which will improve your motor's PF.




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