회로이론
교류전력
2전력계법
2018.8 기출
2전력계법 지시가 700W, 1400W일 때 피상전력은 약 몇 VA인가?
- ① 2425 정답
- ② 2771
- ③ 2873
- ④ 2974
📖 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
\(P=700+1400=2100\)W, \(Q=\sqrt3(1400-700)=1212\)var, \(S=\sqrt{2100^2+1212^2}\approx2425\,\text{VA}\).
\[ P=W_1+W_2,\quad Q=\sqrt3(W_1-W_2),\quad \cos\theta=\frac{W_1+W_2}{2\sqrt{W_1^2+W_2^2-W_1W_2}} \]
풀이
\(P=700+1400=2100\)W, \(Q=\sqrt3(1400-700)=1212\)var, \(S=\sqrt{2100^2+1212^2}\approx2425\,\text{VA}\).