How do you calculate transformer voltage regulation?

How do you calculate transformer voltage regulation?

• A. VR% = [(V_full-load − V_no-load) / V_no-load] × 100
• B. VR% = [(V_no-load − V_full-load) / V_full-load] × 100
• C. VR% = [(V_no-load + V_full-load) / 2] × 100
• D. VR% = [(V_full-load − V_no-load) / V_full-load] × 100

Answer: (B)

Voltage regulation shows how much the secondary voltage falls when the transformer goes from no load to full load, due to the impedance of the windings. When the primary is energized at its rated voltage, the open-circuit secondary voltage is V_no-load. Once the rated current is drawn, the secondary voltage drops to V_full-load. The regulation is expressed as the percentage drop relative to the loaded voltage, because that is the voltage you actually rely on under load: VR% = [(V_no-load − V_full-load) / V_full-load] × 100. This form makes the drop a positive percentage when V_no-load is higher than V_full-load, which is the typical case. Using a denominator of V_no-load or averaging the two voltages would not reflect the practical, load-dependent drop in a meaningful way, and swapping the order of subtraction would yield a negative value. For example, if V_no-load = 120 V and V_full-load = 115 V, regulation is (5/115) × 100 ≈ 4.35%, representing how much the voltage is reduced under load relative to the loaded voltage.

Voltage regulation shows how much the secondary voltage falls when the transformer goes from no load to full load, due to the impedance of the windings. When the primary is energized at its rated voltage, the open-circuit secondary voltage is V_no-load. Once the rated current is drawn, the secondary voltage drops to V_full-load. The regulation is expressed as the percentage drop relative to the loaded voltage, because that is the voltage you actually rely on under load: VR% = [(V_no-load − V_full-load) / V_full-load] × 100.

This form makes the drop a positive percentage when V_no-load is higher than V_full-load, which is the typical case. Using a denominator of V_no-load or averaging the two voltages would not reflect the practical, load-dependent drop in a meaningful way, and swapping the order of subtraction would yield a negative value. For example, if V_no-load = 120 V and V_full-load = 115 V, regulation is (5/115) × 100 ≈ 4.35%, representing how much the voltage is reduced under load relative to the loaded voltage.