Power factor corrector - selecting number of banks and steps

Discussion in 'General Electronics Chat' started by Avinash Govind, May 14, 2009.

  1. Avinash Govind

    Thread Starter New Member

    May 14, 2009
    1
    0
    Hello,

    Can anyone advise on how we decide the number of banks and switching steps that we require for commercially available Automatic power factor corrector units (Merlin Gerin, ABB..)

    Thanking you for your kind reply.
     
  2. rvh002@gmail.com

    Active Member

    May 15, 2009
    118
    2
    Hi, Power facror correction is not an of the shelf buy-it item. Firstly it is only called for in places like factories,mines or industries with a fair amount of motors. They are the main culprits that inherently has a power factor of about 0,8. With powe factor correction you can correct this to about 0,95 normally. (This will save you a fair amount in electricity costs)
    You need to calculate your total load, check with an instrument your power factor when all is running, or look at every motor and compile a list of power factors. All this can the be used to calculate the capacitor bank size. This is normally split into 4 to 5 units which are then controlled by an industrial control unit. Typically the first step is normally about 50% of the total capacitance and the rest is switched in as necessary The complete system is connected to the main supply ditribution board. This is not a DIY system.
    I hope this helps you a bit
     
  3. mik3

    Senior Member

    Feb 4, 2008
    4,846
    63
    Power factor correction does not save you money for the electricity bill. You perform power factor correction because you minimize the reactive power drawn by the factory and thus the losses in the transmission lines are reduced. However, the real power needed by the factory, which is this the power meter measures, will be the same. That is why electric power suppliers penalize customers with low power factors.
     
  4. kubeek

    AAC Fanatic!

    Sep 20, 2005
    4,670
    804
    And that is why you "save a fair amount in electricity cost", isn´t it.
     
  5. mik3

    Senior Member

    Feb 4, 2008
    4,846
    63
    This saves money for the company which produces and distributes electricity. However, it does not save money for the user.
     
  6. kubeek

    AAC Fanatic!

    Sep 20, 2005
    4,670
    804
    No, if the company penalizes you for having low power factor, then you sure save some money if you correct the power factor to the right value and don´t have to pay the penalty.
     
  7. mik3

    Senior Member

    Feb 4, 2008
    4,846
    63
    You won't pay the penalty but you will pay the real power consumed with or without power factor correction.
     
  8. rvh002@gmail.com

    Active Member

    May 15, 2009
    118
    2
    People, I think you miss the point. You pay for the kVA used. It could be supplied by a transformer off the network or a standby generator or whatever. What you use is kW. The basic calculation is kW X power factor equals kVA.
    Now for an example:
    Factory load is 280kW at 0,70PF = 400kVA
    280kW at 0,96PF = 292kVA

    Reduction = 108kVA (27% less load for the same job and therefore a saving)

    And unles you live in some very strange country, that is how electricity is charged.

    Power factor correction is big bussiness in most parts of the world because of the bad POWER FACTOR of induction motors. The installation normally pays for itself in 6 to 9 months. After that, it is money in your pocket. And the suppliers of electricity loves it because it brings down the load on their network.
    Q.E.D.
     
  9. kubeek

    AAC Fanatic!

    Sep 20, 2005
    4,670
    804
    This article http://en.wikipedia.org/wiki/Electricity_meter says that the typical old disk-based meter measures real power and not apparent power ("This produces eddy currents in the disc and the effect is such that a force is exerted on the disc in proportion to the product of the instantaneous current and voltage"). That means you pay for kWh not for kVAh.
     
  10. rvh002@gmail.com

    Active Member

    May 15, 2009
    118
    2
    Well maybe you should read the bit highlited as reactive power on your recomended link.
     
  11. the_guth

    New Member

    Sep 8, 2008
    8
    0
    I'm pretty sure the newer dgital polyphase meters can bill for volt-amps not watts? anyone seen this?
     
  12. mik3

    Senior Member

    Feb 4, 2008
    4,846
    63
    As far as I know electricity meters measure real power and not apparent power.

    Also KVA=KW/power factor and not

    KW*power factor
     
  13. rvh002@gmail.com

    Active Member

    May 15, 2009
    118
    2
    It is impossible for electricity supply companies to measure everybody's power factor and therefore they charge you on kVA use and in most cases on max. demand systems. This subject is now getting a bit long in the tooth, so please do some research and not negative remarks all the time.
    R, van Heerden, Msc. Elec. eng.
     
  14. mik3

    Senior Member

    Feb 4, 2008
    4,846
    63
    Every site I have read on the internet says they measure the electricity in kWh.

    Electric companies don't have to measure each house's power factor because houses don't have large inductive loads to cause a dramatic reduction in the power factor. Power factor correction is applied to big factories.

    Also, the fact that you have MSc does not mean you know everything.
     
  15. recca02

    Senior Member

    Apr 2, 2007
    1,211
    0
    AFAIK industries (not common users) are penalized for low power factor. Thus correcting power factor can save money.
     
Loading...