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I think I understand how to answer this question but am missing how to do a certain part which stops me from getting their.

For this question this is all I know how to do.

cos-1(0.31) = 71.94°

sin(71.94°) × ? = kVAr

I dont know how I am supposed to calculate this missing value "?". Am i on the correct track? The answer to the question is 27.12 to verify your own working.


I don't understand how you've gotten this far without having seen a phase diagram, but here's what it would look like for your problem:


simulate this circuit – Schematic created using CircuitLab

You have been told what the total apparent power is, and you have been told that the real power is 0.31 times the total. Now you just need to figure out the reactive power, which is the third side of the triangle.

  • \$\begingroup\$ To try and get the third side of the triangle I tried -tan(71.94) / 0.31 and added that to the final equation and still dont have the correct answer \$\endgroup\$ – JakeeYm Sep 6 '19 at 13:01
  • \$\begingroup\$ I dont understand what you mean i dont have any sides to the triangle, only the angle being 71.94 \$\endgroup\$ – JakeeYm Sep 6 '19 at 13:02
  • 2
    \$\begingroup\$ Do you understand that power = voltage * current? Do you understand the relationship between the sides and the hypotenuse of a right triangle? Seriously, without these fundamental concepts, you're way out of your depth here. \$\endgroup\$ – Dave Tweed Sep 6 '19 at 13:06
  • \$\begingroup\$ Yes, I understand that \$\endgroup\$ – JakeeYm Sep 6 '19 at 13:09
  • \$\begingroup\$ So 230V x 124A, what does that do for me? \$\endgroup\$ – JakeeYm Sep 6 '19 at 13:14

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