A Transformer has 2% Resistance and 5% Reactance

Answer: B. 4.6%

A transformer has 2% resistance and 5% reactance. Its voltage regulation at full load with 0.8 power factor lagging is 4.6%

 

Solution:

Voltage regulation of transformer is defined as the rise in output voltage expressed as a fraction of full load rated voltage. When full load at specified power factor is reduced to zero, keeping the input voltage constant.

V.R=(V_in-V)/V P.U

Here, Vin= input voltage,

V= rated voltage

And approximated PU regulation for full load at lagging power factor cos 2

 V.R=R_PUcosΦ₂ +X_PUsinΦ₂

Here, R_PU= per unit resistance of transformer

X_PU= per unit reactance of transformer

cosΦ₂ = load power factor angle 

Given,

R_PU=2% 

X_PU=5% 

cosΦ₂ =0.8 

Φ₂=cos^-1(0.8) =36.86° 

sinΦ₂ =sin (36.86°) =0.6 

So, voltage regulation V.R=R_PUcosΦ₂ +X_PUsinΦ₂

V.R=(2%×0.8)+(5%×0.6)=4.6%

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