Consider a balanced star connected system as shown in
figure below. Let VR , VY and VB represent the
phase voltages (Vph) while
line voltages (VL) are given by VRY , VYB and VBR
.
Since it is a balanced
system
It may be observed that when we say line voltage VRY , it means the voltage of terminal R with respect to terminal Y and can be represented in vector terms as
To summarise, in star connection
but 120 ° (electrical) displaced from each other. Negative of a vector is obtained by just reversing it. The figure below shows vectorial addition of phase voltages.
It may be observed that when we say line voltage VRY , it means the voltage of terminal R with respect to terminal Y and can be represented in vector terms as
On the other hand, observation revealed that each line
is in series with its individual phase winding. Hence in a star connection, the
line current in each line is the same as the current in the phase winding to
which the line is connected.
Let current in line R be IR , current in
line Y be IY and current in line B be IB . Since IR = IY = IB=
Iph ( balanced connection) ,
in a star connection it is generalined as
IL= Iph
i.e line currents = phase currents
To summarise, in star connection
1.The line voltages are 120
° apart from each other.
2.The phase voltages are
120 ° apart from each other.
3.The line voltages lead
their respective phase voltages by 30 °.
4.The line voltage
magnitude is √3 times the phase voltage magnitude.
5.The line currents and
phase currents are same.
