Calculation For Voltage Regulation
The voltage regulation up is expressed mathematically by
Positive sign is for lagging power factor and negative sign is for leading power factor.
1.31.1 Zero Voltage Regulation
For lagging power factor and unity power factor, 0V2 > V2. Therefore, we get positive voltage regulation. For leading power factor, V2 starts increasing. At a certain leading power factor, 0V2 = V2and hence regulation becomes zero. If the load power factor is further increased, 0V2 becomes less than V2 and hence regulation becomes negative. For zero voltage regulation, we have
0V2 – V2 = 0
i.e., I2(R02cosθ–X02sinθ)=0
Equation (1.56) shows the leading power factor at which voltage regulation becomes zero.
1.31.2 Condition for Maximum Voltage Regulation
Maximum voltage regulation can be obtained for lagging power factor. For maximum voltage regula-tion, we have 
i.e., –R02sinθ+X02cosθ=0
i.e., 
This is satisfied only when the power factor of the load is lagging. The regulation is maximum when the load power factor angle is equal to the impedance angle of the transformer.
i.e.,
Equation (1.58) shows the power factor of the load at which voltage regulation is maximum.
Figure 1.41 shows the variation of regulation with the power factor of the load. Figure 1.41 also shows that regulation becomes maximum when the power factor of the load is lagging and it becomes zero when the power factor is leading.