Need help with this problem: Power factor

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trobbins313

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It is desired to add a load of 5MW (5000000 watts) at unity power factor to 25 MVA Transformer which is already carrying its rated load at Power factor 0.8 P.F. Lagging. In order not to exceed the transformer MVA Rating, static capacitors will also be added. Determine the minimum MVA rating of the capacitors.

Here is how I went about solving it then I got stuck;

Present KW = 25MVA x 0.8 = 20MW

(sqrt)25?+20? = 15MVA


20 MW + j15
+5MW +j0
= 25 + j15

(sqrt)25?+15? = 29.15 MVA but this is over the rating of the transformer.

Thank you!

Tim
 
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You did good so far. Since you will use all 25 MVA for the 25MW there will be none left for the Mvar. To get rid of all 15 Mvar of inductive load it will take 15 Mvar of capacitors, of course.
 
mivey said:
You did good so far. Since you will use all 25 MVA for the 25MW there will be none left for the Mvar. To get rid of all 15 Mvar of inductive load it will take 15 Mvar of capacitors, of course.
Click to expand...
that would be 20 + 5 +j15 -j15
 
Phil Corso said:
Besoeker...

If the OP answers, I will provide an answer!

Phil
Click to expand...

OK.
Try this.
Would the answer Mivey provided, which addresses the question posed, change if the transformer was say, a cast resin unit, open frame air cooled, or immersed?
I think you know................
 
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