CI Problem 4-30

[stinkycheese]

This is a PF correction problem which I thought I could do in my sleep until I got this one wrong. I calculated that this delta-connected 460V motor, 96A phase current, at a 0.70 lagging pf has S=132kVA <45.6. A capacitor then corrects this to a 0.95 lagging pf and it asks for the real power produced by the motor (I assume they mean consumed).

The solution states that you can simply take 132kVA x 0.95 = 126kW. But isn't P unchanged regardless of PF here, at 132kVA (cos 45.6) = 92kW?

 

[genie17]

You are correct. Their solution is wrong. When you add capacitor to improve the power factor, the current would be reduced. They are taking initial current at the new PF which is wrong.

 

[stinkycheese]

Thanks genie17 for the quick reply!

-sc