Voltage Regulation of Transformer

What is Voltage Regulation?

Voltage Regulation measures the difference in voltage Magnitude between a Component’s sending and Receiving ends. The percentage voltage difference between the voltages of distribution lines, transmission lines, and transformers at no load and at full load is a term frequently used in power engineering.

Explanation of Voltage Regulation of Transformer

Consider a power Transformer that has an open circuit, which means the load is not connected to the Secondary Terminals. The Transformer’s Secondary Terminal voltage in this instance will be equal to its Secondary induced emf E2. When a full load is connected to the Transformer’s Secondary Terminals, rated current I2 flows through the Secondary circuit, causing a voltage drop. The primary winding will now also draw an Equivalent amount of full load current from the source. I2Z2, where Z2 is the Secondary Impedance of the Transformer, gives the voltage drop in the Secondary.

Now if at this loading condition, any one measures the voltage between Secondary terminals, he 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

The equation for the 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 of Transformer in detail. Say lagging power factor of the load is cosθ2, that means angle between secondary current and voltage is θ2.

Here, from the above diagram,

Since the angle between OC and OD may be negligible,. OD is regarded as being nearly equal to OC, i.e.

Voltage regulation 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.

Here, from the above diagram,

Since the angle between OC and OD may be negligible,. OD is regarded as being nearly equal to OC, i.e.

Voltage regulation of transformer at leading power factor,

Zero Voltage Regulation

When a device has “zero voltage regulation,” its “no-load voltage” and “full-load voltage” are the same. This indicates that voltage regulation is equal to zero in the equation above for voltage regulation. This is not realistic and is only conceivable in theory for a Ideal transformer.