3-phase power: getting incorrect phase

Question

Here's my working:

$$ V_P = \frac{V_L}{\sqrt{3}}$$ $$ \therefore V_P = \frac{21.651kV}{\sqrt{3}} = 12.5kV$$ $$ S = 3V_PI_P$$ $$ \therefore I_p = \frac{S}{3V_p} = \frac{2400+j1800kVa}{(3)(12500)} = 80\angle36.86^\circ$$

The solution given in the answer sheet is $$80\angle-36.86^\circ$$

Is there a mistake I made? because this messes up the answers for the rest of the tut. Thanks!

Answer 1

Your equation for complex power isn't correct:

$$S = 3VI^* $$

Remember that you use the complex conjugate of current. This makes \$ I_p = 80 \angle -36.86 ^\circ \$ as the answer sheet suggests.