Also known as the Teetopi or YDelta transform, the startriangle transform allow to
transform a star shaped
tripolar electrical network to a triangle shaped network with he same
behavior and backwards. Suppose we start from the following star/T/Y (the two bottom
nodes are in fact only one same node, as they are supraconductively connected) :
 
0 A  B 0
  


 
C
 


00
The triangle/Pi/Delta we want to transform to is the following :

0 c 0
  
 
 
   
b a
   
 
 
00
The transformation
formulas are the as follows :
a=(A.B+B.C+A.C)/A
b=(A.B+B.C+A.C)/B
c=(A.B+B.C+A.C)/C
And backwards :
A=(b.c)/(a+b+c)
B=(a.c)/(a+b+c)
C=(a.b)/(a+b+c)
This is esily
proved by calculating the
impedance between each node. This gives a set of three equations that can be added / substracted to isolate any of the variables.