Voltage Regulation of Transformer

What is Voltage Regulation ?

The voltage regulation is the percentage of voltage difference between no load and full load voltages of a transformer with respect to its full load voltage.

Explanation of Voltage Regulation of Transformer

Say a electrical power transformer is open circuited means load is not connected with secondary terminals. In this situation the secondary terminal voltage of the transformer will be its secondary induced emf E2. Whenever full load is connected to the secondary terminals of the transformer, rated current I2 flows through the secondary circuit and voltage drops comes into picture. At this situation, primary winding will also draw equivalent full load current from source. The voltage drop in the secondary is I2Z2 where Z2 is the secondary impedance of transformer. If now, at this loading condition any one measures the voltage between secondary terminals, he or she will get voltage V2 across load terminals which is obviously less than no load secondary voltage E2 and this is because of I2Z2 voltage drop in the transformer.

Expression of Voltage Regulation of Transformer

Expression of Voltage Regulation of Transformer, represented in percentage, is


Voltage Regulation of Transformer for Lagging Power Factor

Now we will derive the expression of voltage regulation in detail, say lagging Power Factor of the load is cosθ2, that means angle between secondary current and voltage is θ2
voltage regulation at lagging power factor
Here, from the above diagram,
OC = OA + AB + BC
Here, OA = V2
Here, AB = AEcosθ2 = I2R2cosθ2
and, BC = DEsinθ2 = I2X2sinθ2
Angle between OC & OD may be very small so it can be neglected and OD is considered nearly equal to OC i.e.

E2 = OC = OA + AB + BC
E2 = OC = V2 + I2R2cosθ2 +
............(1)

Voltage Regulation of transformer at lagging power factor,


Voltage Regulation of Transformer for Leading Power Factor

Let's derive the expression of voltage regulation with leading current, say leading Power Factor of the load is cosθ2, that means angle between secondary current and voltage is θ2

voltage regulation at leading poert factor

Here, from the above diagram,

OC = OA + AB − BC

Here, OA = V2

Here, AB = AEcosθ2 = I2R2cosθ2

and, BC = DEsinθ2 = I2X2sinθ2

Angle between OC & OD may be very small so it can be neglected and OD is considered nearly equal to OC i.e.

E2 = OC = OA + AB − BC

E2 = OC = V2 + I2R2cosθ2
..............(2)

Voltage Regulation of transformer at leading power factor,


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