Short Answer:

Voltage regulation in transformers refers to the difference between the no-load and full-load output voltages, expressed as a percentage of the full-load voltage. It shows how much the voltage drops when the transformer is supplying current to a load.

When there is no load connected, the output voltage is slightly higher. As the load increases, the output voltage drops due to internal impedance of the transformer. A good transformer has low voltage regulation, meaning its output voltage remains nearly constant under varying loads.

Detailed Explanation:

Voltage regulation in transformers

Voltage regulation is an important performance parameter of a transformer that tells us how well the transformer maintains its output voltage when the load changes. When a transformer operates with no load, the voltage at the secondary side is at its maximum. But when a load is connected, current starts flowing through the windings, and due to the internal impedance (resistance and reactance), some voltage drop occurs inside the transformer.

This voltage drop results in a lower output voltage under full-load conditions compared to the no-load condition. The difference between these two voltages gives us an idea of how much the voltage is regulated or controlled. The smaller the difference, the better the performance of the transformer in maintaining constant voltage.

Mathematical Expression:
Voltage regulation is calculated using the following formula:

Voltage Regulation (%) = ((No-load voltage – Full-load voltage) / Full-load voltage) × 100

Here:

No-load voltage is the secondary voltage when the transformer is not supplying any current.
Full-load voltage is the secondary voltage when the transformer is supplying the rated load current.

Let’s take a practical example. Suppose a transformer provides 230 V under no-load and 220 V under full-load. The voltage regulation is:

((230 – 220)/220) × 100 = 4.55%

This means there is a 4.55% drop in voltage when the transformer goes from no-load to full-load.

Causes of Voltage Drop:

The drop in voltage mainly happens due to:

Internal Resistance of windings – causes real power loss.
Leakage Reactance – due to magnetic flux not linking both windings perfectly.
Load Power Factor – voltage regulation is worse at lagging power factor (inductive loads).

Good vs. Poor Regulation:

Good voltage regulation: Output voltage stays almost the same under all load conditions. This is ideal for sensitive devices.
Poor voltage regulation: Output voltage drops significantly when load increases. This is not suitable for precise electronic devices.

Effect of Load Power Factor:

Lagging power factor (inductive load): Higher voltage drop → poor regulation.
Unity power factor (pure resistive load): Medium voltage drop → better regulation.
Leading power factor (capacitive load): May cause output voltage to rise → negative regulation.

Why It Matters:

Voltage regulation is important in:

Ensuring stable voltage for sensitive equipment.
Maintaining efficiency in power delivery.
Protecting devices from over-voltage or under-voltage conditions.

Transformers used in communication systems, hospitals, laboratories, and electronic applications must have very low voltage regulation for accuracy and safety.

Conclusion:

Voltage regulation in transformers measures how much the output voltage changes from no-load to full-load. It depends on the internal resistance, reactance, and type of load connected. A transformer with low voltage regulation is preferred, as it ensures stable voltage delivery under varying loads. Understanding voltage regulation helps in selecting the right transformer for reliable and efficient power supply.