Machines
Transformer Voltage Regulation Calculator
Estimate voltage regulation for a declared single-phase or balanced three-phase per-unit series model.
02 / Results
Results
Enter the per-unit series parameters and load point, then calculate.
Calculation method
Ipu = λ(PF − j·s·sinθ); Epu = 1 + Ipu(Rpu + jXpu); regulation = (|Epu| − 1) × 100%.
Worked example
At full load, PF 0.8 lagging, R = 2% and X = 4%: Epu = 1.04 + j0.02, so regulation is approximately +4.01923%.
Frequently asked questions
Does this calculate the loaded terminal voltage?
No. It reports the voltage regulation percentage for the declared per-unit series model; it does not solve a source-voltage operating point.
Can I enter impedance values referred to different sides?
No. Rpu and Xpu must share one consistent base and reference side.
Does a negative result mean a fault?
No. Leading-load conditions can produce negative regulation in this model. It is not a fault or compliance assessment.
Source records
Transformer equivalent circuits and voltage regulation (SRC-061)
Institution: Michigan Technological University
Section: EET3390 Chapter 4, pp. 49–52. Course notes used as model context, not as a standard.
URL on the calculation record: https://pages.mtu.edu/~avsergue/EET3390/Lectures/CHAPTER4.pdf
Verification date: 2026-10-14
Status: verified (record flag, not an external certification)