Y-△等效变换 R 31 2 23 R R 12131 R R12+R23+R31 12 R R 2312 R12+R22+R 23=12+/+2 RoR R r3/ 十n十 R12+R23+R311 2 2 3 3 1 2 3 3 1 3 1 2 2 3 3 1 2 3 1 2 2 1 2 2 3 3 1 1 2 3 1 1 R R R R R r R R R R R r R R R R R r + + = + + = + + = 2 3 1 3 1 3 1 1 2 3 2 3 2 3 3 1 2 1 2 1 2 rr r R r r r r r R r r rrr R r r = + + = + + = + + r 1 r2 r3 1 2 3 Y -  等效变换 R12 R23 R31 1 2 3