13.正相序的三相電源 ， 若負載為平衡Y接當A相相電流為sin(120πt)A， 則A相線電流為何?(A)sin(120πt)A(B)sin(120πt-30°)A(C)1.732sin(120πt-30°)A(D)1.732sin(120πt-120°)A