电路如图所示,Y—Y对称三相电路中原先电流表指示1A(有效值)。后因故障A相断开(即S打开),此时电流表读数为( )。
A 1A B
<img border="0" alt="" src="https://tuku.weimei168.com/uploads/upimg/20251103/23425399_0_1.png"> C
<img border="0" alt="" src="https://tuku.weimei168.com/uploads/upimg/20251103/23425399_0_2.png"> D
0.5A