Jump to content


Photo

Pf Standard


  • Please log in to reply
4 replies to this topic

#1 bestsajid

bestsajid

    Junior Member

  • Members
  • PipPip
  • 2 posts

Posted 23 January 2007 - 07:54 AM

why the motors & generators desine at .8 pf ?

#2 marke

marke

    Posting Freak

  • Moderator
  • PipPipPipPipPipPip
  • 2,600 posts
  • Gender:Male
  • Location:Christchurch, New Zealand

Posted 23 January 2007 - 10:16 AM

Hello bestsajid

Welcome to the forum.
The motors and gnerators are not designed to have a pf of 0.8, it is just something that has to happen as a result of their basic design.

You need to have magnetic flux in order for these machines to work properly. The magnetic flux is caused by current flowing through what is in effect, an electro magnet. This means that there must be an inductive component of the toatl current. - Power faactor must be less than 1.0 due to the magnetic component.

The actual power factor of motors can vary from around 0.6 for small motors to better than 0.9 for very large motors.

I believe that most designers would design for maximum efficitncy and maximum power factor and the figures achieved are the best that they are able to within the frame size.

Best regards,

#3 bestsajid

bestsajid

    Junior Member

  • Members
  • PipPip
  • 2 posts

Posted 24 January 2007 - 07:21 AM

QUOTE(marke @ Jan 23 2007, 10:16 AM) View Post

Hello bestsajid

Welcome to the forum.
The motors and gnerators are not designed to have a pf of 0.8, it is just something that has to happen as a result of their basic design.

You need to have magnetic flux in order for these machines to work properly. The magnetic flux is caused by current flowing through what is in effect, an electro magnet. This means that there must be an inductive component of the toatl current. - Power faactor must be less than 1.0 due to the magnetic component.

The actual power factor of motors can vary from around 0.6 for small motors to better than 0.9 for very large motors.

I believe that most designers would design for maximum efficitncy and maximum power factor and the figures achieved are the best that they are able to within the frame size.

Best regards,

i dont understand plz tel me the motors can design at 12 pf? if no than why?


#4 AB2005

AB2005

    Senior Member

  • Full Member
  • PipPipPipPipPip
  • 406 posts

Posted 25 January 2007 - 01:47 AM

QUOTE(bestsajid @ Jan 24 2007, 12:21 PM) View Post

i dont understand plz tel me the motors can design at 12 pf? if no than why?


Hello,

You havn't basic understanding about power factor. i recommend you to read about power factor then ask question here.

http://www.lmphotonics.com/pwrfact.htm


"Don't assume any thing, always check/ask and clear yourself".

#5 marke

marke

    Posting Freak

  • Moderator
  • PipPipPipPipPipPip
  • 2,600 posts
  • Gender:Male
  • Location:Christchurch, New Zealand

Posted 25 January 2007 - 03:26 AM

Hello bestsajid

The power factor can never exceed 1.0 That is the power factor of a purely resistive load.

An induction motor must be inductive, otherwise it would not function. Therefore, the power factor must be a lagging power factor less than 1.0
The actual power factor is a result of the magnetising current and leakage reactance of the motor, and although the designers try to maximise the efficiency and power factor, on small motors both are lower than on large motors.
If the small motors were wound on a larger frame (at higher cost) then they would probably have a higher power factor and efficiency.

Best regards,




0 user(s) are reading this topic

0 members, 0 guests, 0 anonymous users