Concept of transformation :
By the application of kirchoffs laws some problems cannot be solved and finds great difficulty due to number of equations. Such problems can be simplified by using star to delta or delta – star transformations
The figure show two systems of connections of resistances. In star or ‘Y’ connection there is a common point for all the three resistors, and in delta or mesh connection the three are connected in series to form the loop and the
junctions are taken out to form three supply points. The common point in star connection is called ‘Neutral’. The delta connection will have no neutral point Assuming that the star connection is to be converted into delta connection. If the two networks are to be identical the resistance between any pair of lines will be the same when the third loop is opened.
How to remember : The equivalent delta resistance between any two points is given by the sum of star resistances between those terminals plus the product of these two star resistances divided by the third resistor.