A Transformer has 2% Resistance and 5% Reactance

By Varadi Hema|Updated : July 26th, 2022

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

  1. 5.3%
  2. 4.6%
  3. 0.53%
  4. 0.46%

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=(Vin-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=RPUcosΦ2 +XPUsinΦ2

Here, RPU= per unit resistance of transformer

XPU= per unit reactance of transformer

cosΦ2 = load power factor angle 

Given,

RPU=2% 

XPU=5% 

cosΦ2 =0.8 

Φ2=cos-1(0.8) =36.86° 

sinΦ2 =sin (36.86°) =0.6 

So, voltage regulation V.R=RPUcosΦ2 +XPUsinΦ2

V.R=(2%×0.8)+(5%×0.6)=4.6%

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