회로이론
교류전력
2전력계법
2019.4 기출
2전력계법에서 지시가 500W, 1500W일 때 피상전력은 약 몇 VA인가?
- ① 2000
- ② 2310
- ③ 2646 정답
- ④ 2771
📖 해설
2전력계법(3상전력)
\[ P=W_1+W_2,\quad Q=\sqrt3(W_1-W_2),\quad \cos\theta=\frac{W_1+W_2}{2\sqrt{W_1^2+W_2^2-W_1W_2}} \]
풀이
\(P=W_1+W_2=2000\)W, \(Q=\sqrt3(W_2-W_1)=\sqrt3\times1000=1732\)var. \(S=\sqrt{P^2+Q^2}\approx2646\,\text{VA}\).
\[ P=W_1+W_2,\quad Q=\sqrt3(W_1-W_2),\quad \cos\theta=\frac{W_1+W_2}{2\sqrt{W_1^2+W_2^2-W_1W_2}} \]
풀이
\(P=W_1+W_2=2000\)W, \(Q=\sqrt3(W_2-W_1)=\sqrt3\times1000=1732\)var. \(S=\sqrt{P^2+Q^2}\approx2646\,\text{VA}\).