Page 435 - Basic Electrical Engineering

Figure 4.8 (a) Balanced star-connected system; (b) phasor diagram

To derive the relation between V and V , consider line voltage V RY .
L
Ph

V RY = V RN + V NY

V RY = V RN + (−V YN )

Similarly V YB = V YN + (−V BN )

and V BR = V BN + (−V RN )

The procedure for drawing the phasor diagram of Fig. 4.8 (b) is as follows.
Draw three phasors V , V , and V representing the phase voltages. These
Y
R
B
voltages are of equal magnitude but displaced by 120º. The line voltage
phasors, V RY , V YB , V are drawn by vectorially adding the phase voltages.
BR
For example, to draw line voltage V RY we have to add the phase voltages as

V RY = V RN + V NY = V RN + (– V YN )

The phasor V YN is obtained by reversing V NY . V RY is obtained by vectorially
adding V RN and V YN as has been shown in Fig. 4.8 (b). Similarly the other