Voltage Regulation of Transformer

Voltage Regulation Of Transformer

Hello everyone,
In this post we are going to discuss about Voltage regulation of a transformer.

Read here : Differences Between Core And Shell Type Transformers

What is meant my Voltage regulation of transformer?
Voltage regulation of a transformer may be defined as the difference between no load voltage of the secondary terminal of a transformer and full load voltage of the secondary terminal of that transformer at a certain power factor. Voltage regulation of a transformer is expressed in percentage of either no load secondary terminal voltage or full load secondary terminal voltage.

Read here : EMF Equation of Transformer & Voltage Transformation Ratio

Objective to calculate voltage regulation of transformer:

Calculating voltage regulation of transformer gives how much efficiently the transformer is resisting the voltage changes from no load to full load. If there is no change in value of secondary voltage from no load to full load then the transformer is ideal and has voltage regulation 0%. So the lower the value of voltage regulation the higher is the performance of the transformer. 

 Procedure to calculate voltage regulation of transformer:

Consider a transformer which is at no load which means the secondary of the transformer is open circuited. In this case the secondary voltage of the transformer and induced emf are same let it be E2 . Now full load is connected to the secondary of a transformer. In this case current I2 passes in the secondary which will lead to voltage drop and is given by I2Z2. Where Z2 is called secondary impedance of transformer. During this situation primary winding will draw equivalent full load current. Because of the voltage drop the secondary voltage cannot be E2 anymore so secondary induced emf will be V2.

Equivalent circuit for calculating voltage regulation of transformer:



Equation for calculating voltage regulation of a transformer:


Voltage regulation of transformer in percentage can be represented as:

Voltage regulation % = (E2-V2/V2)×100%. This is called regulation down. Power factor is specific.

Calculating voltage regulation of transformer for lagging power factor:

Now lets derive the expression for calculating voltage regulation of transformer for lagging power factor.

Phasor diagram:



here cos𝚹2 is lagging power factor

From diagram,

                       OC = OA + AB + BC
                       
                       OA = V2
                       
                       AB = AEcos𝚹=  I2R2cos𝚹2
          
                       BC=DEsin𝚹2=I2R2sin𝚹2

Angle between OC and OD is very less so OC is approximately equal to OD.

                 E2 = OC = OA + AB + BC.

                 E= OC = V2 + I2R2cos𝚹2 + I2R2sin𝚹2

Now voltage regulation of transformer at lagging power factor is,
Voltage regulation% = (E2-V2/V2) × 100%

Voltage regulation%=( I2R2cos𝚹2I2R2sin𝚹2V2 ) ×100%.

Calculating voltage regulation of transformer for leading power factor:

Now lets derive the expression for calculating voltage regulation of transformer for leading power factor.

Phasor diagram:




here cos𝚹is leading power factor
From diagram,

                         OC = OA + AB - BC

                          OA = V2
                       
                         AB = AEcos𝚹2 = I2R2cos𝚹2
          
                         BC = DEsin𝚹2 = I2R2sin𝚹2  

Angle between OC and OD is very less so OC is approximately equal to OD.

                         E2  = OC = OA +AB - BC.

                          E= OC = V2 + I2R2cos𝚹2 - I2R2sin𝚹2

Now voltage regulation of transformer at leading power factor is,
Voltage regulation% = (E2-V2/V2) × 100%

Voltage regulation%=(I2 R2cos𝚹2 - I2R2sin𝚹2 /V2 ) ×100%.

Thus we have learnt what is voltage regulation of transformer and derived expressions for voltage regulation of transformer for lagging and leading power factors. 
You can download this article of Voltage Regulation OF Transformer as a PDF here.