transformer voltage regulation formula

Definition of Voltage Regulation.

The primary voltage of any transformer is kept constant and as the load increases, the secondary terminal voltage decreases. This voltage drop is due to the resistance reaction of the transformer coil.

The voltage regulation is obtained by dividing the total voltage drop from no load to full load by the full load voltage. This regulation is usually expressed as a percentage.


VR= voltage regulation,

`V_{NL}`= no load voltage,

`V_{FL}`= full load voltage,

This Regulation may also be published in the primary term. The lower the standard of regulation, the better During the testing of different transformers at the same KVA rating, the lower the regulation value, the better.

Regulation can again be expressed as "up" and "down" E. g .


and `\%V.R(up)=\frac{V_{N.L}-V_{F.L}}{V_{F.L}}\times100`

The factors to consider when determining voltage regulation are: -

  1.  Voltage, current and frequency = These will mean rated values ​​when determining transformer regulation.

  2. Load = Rated load if no specific information is provided

  3.  Web form = sine wave voltage |

  4.   Load power factor = Load power factor is usually given But if you don't say something like that, it will mean 100% power factor

  5.  Temperature = At ​​all loads the reference temperature is usually 75 C

Voltage regulation depends a lot on the type of load

Electric load: 3 types of electric load Namely: -

  1. Resistive load: Heater, Electric Iron, Incandescent Lamp, etc. The power factor of such load is always unity

  2.  Inductive load: induction motor, transformer, etc. Also, most of the loads belong to inductive loads. Power factor lagging occurs in such loads.

  3.  Capacitive load: capacitor, synchronous condenser, etc.  Power factor leading occurs in such loads.

Equation of voltage regulation.

The no-load voltage of voltage regulation usually depends on three factors Namely: -

  1.  Unity Power Factor,

  2.  Lagging Power Factor,

  3.  Leading Power Factor,

1. Unity Power Factor: This happens in the case of resistive load. 

Resistive Drop = IsRe ”

Inductive Drop = IsXe”

Impedance Drop = IsZe ”


The drops are captured at secondary in the no load state from the triangle ACD -





2. Lagging Power factor: - in the case of load it is Inductive.

Resistive Drop = IsRe ”

Reactive Drop = IsXe”


Triangle I get from ACF: -






3. Leading power factor: - It happens in case of capacitive load

Resistive Drop = IsRe ”

Reactive Drop = IsXe”


Triangle I get from ADF: -






Capacitive In the case of loading the value of voltage regulation is negative 

Near Formula Stand Diameter Voltage Regulation Diagnosis: -

Total near voltage drop secondary of the transformer,





Q = Theta

The positive (+) sign is used for inductive load and the negative (-) sign is used for a capacitive load. The lower the voltage regulation value, the better the device. 

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