# Total Approximate Voltage Drop Of A Transformer

During no-load condition, induced voltages at the primary and secondary windings are equal to the applied voltage and secondary terminal voltage respectively. If _{0}*V*_{2} be the secondary terminal voltage at no load, we can write *E*_{2} = _{0}*V*_{2}. Let *V*_{2} be the secondary voltage on load. Figure 1.40 shows the phasor diagram of a transformer referred to as secondary.

In Figure 1.40, *R*_{02} and *X*_{02} are the equivalent resistance and reactance of the transformer, respec-tively, referred to as secondary side. With *O* as centre, an arc is drawn in Figure 1.40, which intersects the extended *OA* at *H*. From *C*, a perpendicular is drawn on *OH*, which intersects it at *G*. Now *AC* = *AH*represents the actual drop and *AG* represents the approximate voltage drop. *BF* is drawn perpendicular to *OH*. *BE* is drawn parallel to *AG*, which is equal to *FG*.

The approximate voltage drop

= *AG* = *AF*+ *FG* = *AF*+ *BE*

= *I*_{2}*R*_{02}cos*θ*+*I*_{2}*X*_{02}sin*θ* (1.39)

**Figure 1.40** Phasor Diagram of a Transformer Referred to as Secondary

This approximate voltage drop shown in Equation (1.39) is for lagging power factor only.

For leading power factor, the approximate voltage drop will be

= *I*_{2}*R*_{02}cos*θ*–*I*_{2}*X*_{02}sin*θ* (1.40)

where ‘+’ sign is for lagging power factor and ‘-’ sign is for leading power factor.

The above calculation is referred to as secondary. It may be noted that voltage drop referred to as primary is

*I*_{1}*R*_{01}cos*θ*±*I*_{1}*X*_{01}sin*θ* (1.41)

∴% voltage drop in secondary is=

=*v _{r}*cos

*θ*±

*v*sin

_{x}*θ*(1.42)

where

and