No-load voltage: The secondary terminal voltage of transformer when no load is connected to the transformer is known as the no-load voltage of the transformer. At no load, the secondary terminal voltage will be equal to induced EMF in the secondary winding.
 
So, no-load voltage = E2 volts
 
Full load voltage: It is the secondary terminal voltage of transformer when a rated load is connected to the transformer. We will denote it by V2.
 

Voltage Regulation of Transformer Definition

 
The voltage regulation of transformer is defined as the change in secondary terminal voltage (V2) from no-load to full load at constant primary voltage and temperature. It is expressed as a percentage of the secondary no-load voltage.
 
Mathematically, % Regulation of transformer = (E2 – V2) x 100 / E2
 
When a transformer is loaded a voltage drop in primary and secondary impedances of transformer takes place. As the load current increases, this voltage drop will increase. This will reduce the secondary terminal voltage V2. The ideal value of voltage regulation of transformer is 0%.
 
The approximate expression for the total voltage drop (E2 – V2) in a transformer as referred to secondary is given by
 
regulation of transformer
 
Where,
R02 = equivalent resistance of transformer referred to secondary
X02 = equivalent reactance of transformer referred to secondary
R01 = equivalent resistance of transformer referred to primary
X01 = equivalent resistance of transformer referred to primary
 
Here it has been assumed that φ1 = φ2 = φ.
 
The positive sign is used for a lagging power factor and the negative sign for a leading power factor.
 
It is clear from the above expressions regulation of transformer does not depend only on the magnitude of load current. But it also depends on the type of load. The transformer regulation is positive for the resistive and inductive loads but it can be negative for the capacitive loads.
 
We can determine the values of R01, X01, R02, X02 of a transformer from short circuit test and calculate percentage regulation of transformer.
 

Transformer Regulation Calculation

 
Example: A 100 kVA transformer has 400 turns on the primary and 80 turns on the secondary. The primary and secondary resistances are 0.3 Ω and 0.01 Ω respectively and the corresponding leakage reactances are 1.1 and 0.035 Ω respectively. The supply voltage is 2200 V. Calculate:

  • equivalent impedance referred to primary and,
  • the voltage regulation and the secondary terminal voltage for full load having a power factor of 0.8 leading.

 
Solution: K = 80/400 = 1/5,
 
R1 = 0.3 Ω,
R01 = R1 + R2/K2 = 0.3 + 0.01/(1/5)2 = 0.55 Ω
X01 = X1 + X2/K2 = 1.1 + 0.035/(1/5)2 = 1.975 Ω
Z01 = 0.55 + j 1.975 = 2.05 ∠74.44o
 
Z02 = K2Z01 = (1/5)2 (0.55 + j 1.975) = (0.022 + j 0.079)
 
No-load secondary voltage = KV1 = (1/5) × 2200 = 440 V,
I2 = 10 × 103/440 = 227.3 A
 
Full-load voltage drop as referred to secondary
= I2 (R02 cos φ − X02 sin φ)
 
= 227.3 (0.022 × 0.8 − 0.079 × 0.6 ) = − 6.77 V
 
% regn. = − 6.77 × 100/440 = − 1.54
 
Secondary terminal voltage on load = 440 − (− 6.77) = 446.77 V
 
Thanks for reading about transformer regulation calculation.
 

Transformer–10 | Objective Type Question Answers

#1 Which of the following statement concerning parallel operation of transformers is incorrect?

Transformers must have equal kVA

#2 Current transformers for meters and relays usually have

5-A  secondaries

#3 All day efficiency is the ratio of output to input in

kWh during 24 hours

#4 While performing back-to-back test, the amount of power consumed is equal to

iron and copper losses of two transformers at full load

#5 The purpose of performing Surnpner’s test is mainly to find out

the temperature rise on full load economically

#6 When 240 V D.C. supply is given to an unloaded 220 V, 50Hz transformer

primary will carry heavy current and may possibly burn

#7 In a transformer, if the magnitude of magnetizing current is more

its power factor will become low on lagging side

#8 In measuring voltage or current by means of instrument transformer

only ratio errors need to be considered

#9 In which of the following the highest rating transformer is likely to find application ?

Generator

#10 In a transformer maximum voltage regulation occurs when the power factor of the load is

lagging

#11 In a transformer minimum voltage regulation occurs when the power factor of the load is

leading

#12 When a delta connected primary of a 3-phase transformer is connected to 3-phase supply

magnetizing current in phase winding will carry third harmonics but line current will be free from it.

#13 Scott connections are used to convert

three-phase supply to two-phase supply

#14 Which of the following 3-phase connections of transformer create disturbances in communication systems

star/star

#15 Delta-delta power transformer is protected by current transformer having

star/star connections

#16 Star-star power transformer is protected by current transformer having

delta/delta connections

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Categories: Transformer

3 Comments

windingproducts · 01/09/2018 at

Toroidal winding machine has included changing parameters with the support of controller unit and this is multi-reason bound controller. The setup can be changed to pass on the sensible application for fundamental application. In like way, the toroidal winding machine has included with major stepper engine drive, DC engine drive, and power supplies in a control box. All around, this sort of winding machines has controlled for transformers.Choke winding

jagannath · 07/05/2019 at

While performing back-to-back test, the amount of power consumed is equal to
iron and copper losses of two transformers at full load + iron and copper losses of voltage injection unit

cable size calculator · 11/18/2019 at

Hi there. I could never understand these calculations in class. You have explained in a very simple and easy way. My assignment got rejected twice because I messed up the calculations. Hopefully, I’ll pass my quiz now.

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