Question

Briefly describe the meaning of the expression star connected as applied to 3phase AC practice. What is the ratio of he maximum line voltage to the maximum phase voltage in each case.

Star or Y connection shows the arrangement as follow.

The 3 coil or phase winding are connected so that either all the starts or finishes are joined together to form the star point i.e. corresponding ends are connected together.

Similarly the supply lines are connected to the free ends remote from the start point.

Consider the phasor diagram

Let the line voltage Vr-y = 2X

But X / Vr = cos 30deg

X = √3/2 Vr or 2X = √3Vr

Hence Vr-y = √3Vr

Or voltage between lines = √3 X a phase voltage

Thus Vl =√3Vph