Voltage regulation of Transformer

Voltage Regulation of Transformers

Introduction

Voltage regulation is an important performance parameter of a transformer. It indicates how much the secondary terminal voltage changes as the load varies, while the primary input voltage remains constant.

In simple words:
👉 Voltage Regulation = % change in secondary voltage from no-load to full-load condition.

Good transformers are expected to have low voltage regulation, meaning they maintain nearly constant secondary voltage under varying load conditions.

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Definition of Voltage Regulation of Transformer

Voltage regulation of a transformer is defined as:

$$\text{Voltage Regulation} = \frac{V_{no\ load} - V_{full\ load}}{V_{no\ load}}$$

Where:

• $V_{no\ load}$ = Secondary terminal voltage at no load

• $V_{full\ load}$ = Secondary terminal voltage at full load

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Types of Voltage Regulation

1. Down Regulation (most common in practice):
   When load is connected, the secondary voltage drops due to internal impedance of the transformer.

   Formula:

   $$\% \text{Regulation (Down)} = \frac{V_{no\ load} - V_{full\ load}}{V_{no\ load}} \times 100$$

2. Up Regulation (less common):
   In some leading power factor loads (like capacitive loads), the secondary voltage may rise when load is applied.

   Formula:

   $$\% \text{Regulation (Up)} = \frac{V_{no\ load} - V_{full\ load}}{V_{full\ load}} \times 100$$

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Example Calculation

Suppose a single-phase transformer has:

• No-load secondary voltage ($V_{no\ load}$) = 230 V

• Full-load secondary voltage ($V_{full\ load}$) = 210 V

Then:

$$\% \text{Regulation} = \frac{230 - 210}{230} \times 100$$ $$= \frac{20}{230} \times 100 = 8.69\%$$

👉 The transformer has 8.69% voltage regulation.

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Significance of Voltage Regulation

• Low regulation (%) → Better transformer performance.

• Typical range: 0.5% to 5% for large power transformers.

• High regulation means large voltage drop, poor efficiency in supplying constant voltage.

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Practical Notes for Engineers

• Voltage regulation depends on power factor of the load:

  • Lagging power factor → Voltage drop (positive regulation).

  • Leading power factor → Voltage rise (negative regulation).

• Efficiency and regulation are two key parameters considered in transformer design and testing.

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✅ Summary:
Voltage regulation of a transformer shows how much the output voltage changes from no-load to full-load. It is ideally low, ensuring stable voltage supply to loads.

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