ElectricalPower SystemseasyFE ExamCourseworkPE / Advanced

Voltage Regulation of a Transformer

A transformer delivers $240\ \text{V}$ at no load and $230\ \text{V}$ at full load.

Find the percentage voltage regulation.

Given

Vnl	240 V	No-load voltage
Vfl	230 V	Full-load voltage

Hint 1

Voltage regulation measures how much the output sags from no load to full load.

Hint 2

The difference is normalised — but against which voltage?

Hint 3

By convention, the denominator is the full-load voltage.

Worked solution — try the problem first

$\%VR = \frac{V_{NL} - V_{FL}}{V_{FL}} \times 100$

$= \frac{240 - 230}{230} \times 100 = \frac{10}{230} \times 100 = 4.35\%$

$\boxed{\%VR = 4.35\%}$

The denominator is full-load voltage, not no-load. Using 240 gives 4.17% — close enough to look plausible, which is exactly what makes it a dangerous error. The convention normalises against the voltage the load actually receives.

Lower regulation means a stiffer supply. A large distribution transformer might achieve 2-3%; a small one with high winding impedance could exceed 6%.

Concepts:Voltage regulationTransformersPower quality

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