△Y变换的等效条件 1Y △ 12△ 31△ R R R u12Y 12 R R 2Y Y+ 2 R 23Y 等效的条件:i1A=i1y,2△=2y,i3△=3y 且a12=12y,234=123y,u31A=31yR12 R31 R23 i3  i2  i1 1 2 3 + + + – – – u12 u23 u31 R1 R2 R3 i1Y i2Y i3Y 1 2 3 + + – + – – u12Y u23Y u31Y 等效的条件: i1 =i1Y , i2  =i2Y , i3  =i3Y , 且 u12 =u12Y , u23 =u23Y , u31 =u31Y —Y 变换的等效条件: