Where Compensate a transformer how load inductive ?

[neira]

Where may conect a capacitor bank to compensate the inductive kvar of a power transformer 4160 / 480 Vac, 3~,60Hz, on the 4160 V or 480 V? The reader bill energy is on the 4160 V side.
Thanks

 

[busbar]

Please search this site using terms like "PF correction" and "power-factor correction." There has been considerable discussion and links presented here.

 

[advidana]

Are you really compensating the kvar of the transformer or the motor loads. I would place the capacitors on the same voltage line as the motors or what ever device is causing the major inductance.

 

[neira]

Adividana, It's to compensate the inductive load of power transformer, only.

 

[rbulsara]

I would place the caps on the LV side (load side).

This lowers the kVA burden on the transformer and redcues I^2*R losses in the tranformer.

LV caps would also be less expensive and requiring lesser degree of competence to operate and maintain.

As far as the primary side meter goes it would see the net corrected kVA or kVAR of the system, regardless of where the capacitor is.

I must add that I never added a PF cap only for a transformer.

 

[advidana]

The transformer has no load and you want to compensate for that condition? Just disconnect the transformer.

 

[stevenal]

Interesting question. In general, you want to place caps close to the inductive loads you are compensating for, and avoid crossing transformers in order to avoid losses between the load and caps. But in the case of the transformer, your inductance is in both windings. The ideal solution is to place the caps on both sides in proportion to the inductive losses contributed by each winding. In practice, I think insulation levels and the associated cost difference will argue for the 480 caps.

Rbusara,

Assuming the 480 load is purely resistive, VAr flow from your low side caps flows back into the transformer, some of it crossing over the turns ratio to compensate for the high side winding. Have you really lowered the (I^2)*R losses in the transformer? You've reduced the VArs flowing in from the high side, but increased them on the low. Since the losses increase with the square of the current, high side resistance must be that much higher than the low side to come out even.

 

[rbulsara]

stevenl:

If you have all resistive load, the power factor is nearly unity and no need to apply any PFC? What is your point?

If you add PFC to a unity pf load, the load becomes leading you increase the KVA (same effect as a lagging pf) and obviously you increase the I^R losses!!!

 

[stevenal]

Rbusa,

Take another look at neira's posts. He is not compensating for the downstream load, only for the transformer. Load by itself is resistive, or close enough.

 

[advidana]

I do not understand why you would want to correct pf of just the transfomer.

If you do just have resistive loads and need a pf correction for only the transformer. I would think that inductive pf would be low on a typical transformer that supplies 480v on the secondary.

I believe it would not be cost effective to correct just for pf for bthis condition. The first cost, maintenance and other problems that the capacitor bank would experience are not worst it.

What kind of pf readings are you getting that you think you need pf correction?