Question

A 2300/230 V, 1-phase transformer, maximum possible voltage regulation is 5% and occurs at p.f. of 0.25. The load voltage at full load, power factor of 0.8 lead is________V.

• A. 234.46

Answer 1

The correct option is A 234.46
Fro maximum voltage regulation of transformer impedance angle ${\theta }_s$ = Power factor angle $\varphi$

${\theta }_s=co{s}^{-1}0.25$

${\theta }_s={75.520}^{\circ }$

$\text{\%z = V.R}$

$\text{and \%z = 5\%}$

$\text{Now at 0.8 lead,}\varphi =co{s}^{-1}0.8={36.86}^{\circ }$

$\text{\%V.R = \%}z\cos ({\theta }_s+\varphi )$

$\text{=5\% cos}({75.52}^{\circ }+{36.86}^{\circ })$

$\text{\%V.R.=}-\text{1.903}$

$\text{\%V.R. =}\frac{V_{R\left(atnoload\right)}-V_{R\left(atfullload\right)}}{V_{R\left(atfullload\right)}}$

$\frac{-1.903}{100}=\frac{230-V_{Rf}}{V_{Rf}}$

$V_{Rf}(1-\frac{1.903}{100})=230$

$\text{0.98097}{V}_{Rf}\text{= 230}$

$V_{Rf}\text{= 234.46 Volts}$