Relation between VA and W

Discussion in 'The Projects Forum' started by GT82, Jan 20, 2011.

  1. GT82

    Thread Starter New Member

    Jun 30, 2010
    Please could someone clear this up for me as I keep getting differing information. As far as I know electrical utility companies charge residential consumers in W so power factor does not count. I am looking to convert a house to LED and energy saver lamps and these lamps have very bad power factors. I need to size the transformers for VA not W correct? As the actual power drawn from the transformer will be in VA.

    Secondly if I know the power factor is 0.7 is it correct to say VA=W/pf? This makes the actual consumption huge!
  2. SgtWookie


    Jul 17, 2007
  3. debjit625

    Well-Known Member

    Apr 17, 2010
    VA is the unit for Apparent power,i.e.. the combination of true power and reactive power.Transformer is an inductor and works with AC so their will be reactive power and their will be some true power also for transformer and load, so yes you need to size the transformer for VA (transformers are rated in VA only).

    and yes this is correct....
    Power factor (pf) = True power (W) / Apparent power (VA).

    Good Luck