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In which side addition a capacitor bank could play a key role of compensating the reactive power absorbed by a transformer and achieve the same power factor calculated at the load side? primary or secondary side ? Power factor in the secondary side (after compensation) is: 0.94

oussama aatiq
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  • What makes you think losses can be reduced at all? – Andy aka Sep 04 '16 at 17:44
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    Possible duplicate of [Is it possible to put capacitor bank at the primary side of transformer?](http://electronics.stackexchange.com/questions/256034/is-it-possible-to-put-capacitor-bank-at-the-primary-side-of-transformer) – CL. Sep 04 '16 at 17:45
  • The question is modified to be more clear – oussama aatiq Sep 04 '16 at 17:57
  • If you want to improve an existing question, use the "edit" button below the question. Do not post new questions which are duplicates of existing ones, especially not of questions you asked yourself. –  Sep 04 '16 at 18:02
  • I believe you need to share more information about what you want to do. Why would you need the same power factor as in the load? You problably only need the power factor to be near 1 to lower the electricity bill thus placing the capacitor load at the primary is best. – Krauss Sep 04 '16 at 18:12
  • It's still unclear what do you want to achieve. What do you mean by "power factor"? What is the coefficient of coupling of primary and secondary windings for this transformer? Why do you want to compensate reactive power? In transformers with high coefficient of winding coupling reactive component depends heavily on the load itself, not only on transformer. – BJovke Sep 04 '16 at 18:13
  • @BJovke: See [Power factor](https://en.wikipedia.org/wiki/Power_factor) and http://electronics.stackexchange.com/questions/247752/why-do-we-want-higher-power-factor-in-ac-motors/247757#247757. It is universally used in large industrial installations. – Transistor Sep 04 '16 at 19:01
  • "Power factor" can mean a lot of things, it's simply not accurate enough name. And in this context it could be wrong. Optimal phase shift between voltage and current at "load" side might not be at highest "power factor". It all depends on what your load is and what your circuit actually does. – BJovke Sep 05 '16 at 19:52

2 Answers2

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reactive power absorbed by a transformer

Reactive power is the continuous transfer of energy back in forth between two components that store energy. Reactive power by definition is not absorbed, dissipated or converted to work.

The reactive current required to magnetize a transformer causes a very small amount of reactive power compared to the total power rating of a transformer. That reactive power is considered to be insignificant and no compensation is required.

The kVAR of reactive power due to loads connected to the transformer is reflected to the primary at essentially the same level. It can be compensated by connecting capacitors on either side of the transformer. The advantage of placing the capacitors on the secondary is that compensating the power factor reduces the current that the transformer needs to carry. That reduces losses in the transformer and allows the transformer to supply additional load current because it doesn't need to supply reactive current.

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Placing power-factor correction capacitors on the transformer secondary side is the normal practice. I can think of a couple of good reasons for this.

  • Lower voltage capacitors can be used. More capacitance will be required but the volume will probably be about the same and the cost will probably be lower.
  • Lower voltage switchgear can be used. There may be trade-offs between low-voltage / high-current and vice-versa.
  • PF correction on the LV side means that the transformer current is reduced. For a given VA rating more kW can be drawn from the transformer when the LV side is corrected.
  • For a given kW demand the voltage drop on your transformer secondary will be lower with LV (secondary) correction as the current is reduced.

Your electricity provider won't care which you do. They'll be happy that your power factor is close to unity. You will reduce the amount of useful energy your transformer can supply if you do the correction on the high side.

Transistor
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