Correct Answer - Option 1 : 4.6%

Concept:

In transformer voltage regulation is given by,

Voltage regulation = x (Rpu cosθ ± Xpu sinθ)

Where x = fraction of load

Rpu = resistance in pu (we can use % resistive drop in fraction)

Xpu = reactance in pu (we can use % reactive drop in fraction)

+ for lagging load

– for leading load

Calculation:

Given that, transformer is working at 0.8 lagging power factor at full load

⇒ cos θ = 0.8, sin θ = 0.6

x = 1

Rpu = 2%

Xpu = 5%

%V.R. = 1 × (2 × 0.8 + 5 × 0.6) = 4.6%