Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Power Factor Correction VARS?

  1. Apr 29, 2012 #1
    Hi Guys-

    So, I'm new to the Power Quality world but have worked in the VFD world for some years.

    The term "KVARS or VARS" is new to me.

    Looking for a simple explanation and how they work in a system.

  2. jcsd
  3. Apr 29, 2012 #2


    User Avatar

    Staff: Mentor

    KVARs are like watts in that they represent current through your meters and (usually) consequent billing by your electricity retailer. But unlike watts, KVARs do not perform work or do anything productive. KVARs are a consequence of non-resistive devices in your workshop, such as motors and solenoids. KVARs represent losses to you, and losses to the electricity supplier because he is supplying you with more current than you really need for the work your motors are performing. There are ways to reduce your KVARs, but none of these measures is inexpensive so efforts are almost never made to try to reduce KVARs right down to zero, through some measure of reducing them is encouraged by the supplier's punitive billing structure.
  4. Apr 30, 2012 #3


    User Avatar
    Gold Member

    In regards to motors and most inductive loads.......

    Watts is the power that is measured at the shaft of the motor....in other words, how much power the motor makes at it's shaft is the watts or HP of the motor. KVA is the amount of electrcity it takes to power that motor. KVAR is the amount of reactive power in the power triangle.

    If a motor it rated at 10 Killowatts (about 13.5 HP) and uses 13 KVA of power......

    To find the power factor....divide watts by VA......in this case 10/13 = .77 PF.

    To find full load amps you need to base your amps on KVA....not watts.

    Assuming 480 volts three phase......


    Current will equal 15.65 full load amps per phase. Do not base full load amps on watts!

    In regards to the power triangle....picture a triangle with one vector on the x axis...this is watts. Now picture another vector at 20 or 30 degrees or so from the same axis. Now connect the triangle at the end of those two vectors and the vertical line you just drew is reactive power. You can use simple geomotry to figure exact numbers.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook