Voltage Regulation

The change in secondary voltage from no load to full load, as a percentage of full-load voltage.

Intermediate

$\text{VR} = \frac{V_{nl} - V_{fl}}{V_{fl}} \times 100\%$

Approximate formula (per-unit values):

$\text{VR} \approx \varepsilon_r\cos\phi \pm \varepsilon_x\sin\phi$

using + for lagging and − for leading power factor. A leading load can even produce negative regulation (the voltage rises with load). Distribution transformers use tap changers to keep the customer voltage within limits.

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