In this system three similar ends of the phase windings are connected at one point which is known as the star point or neutral point. The remaining three ends are brought out for supply this supply system is known as three phase four wires supply system as shown in Fig. 16.5.
Fig. 16.5 Star connection
Fig. 16.5 (b). Vector diagram
This system has got the following characteristics:
(i) Three similar ends (start or finish) of the three phase windings are connected to one point that is known the star or neutral point.
(ii) The current in neutral wire will be the vector sum of all phase currents. There is no current in the neutral wire in case of balanced
(iii) The phase voltage = line voltage/√3
(iv) The line current is equal to phase current.
(v) The line voltage leads the phase voltage by 30 elect.
(vi) The power is W 3 x Phase power
where Ep is the phase voltage and Ip the phase current.
so the power=a x line voltage x line current x power factor.
In case of unbalanced loads the total power can be given by the algebraic sum of the individual phase powers. This system is generally used because for domestic and industrial purposes both voltages light and power are possible from the same line.