When to Use This Calculator
Use this calculator when a transformer, source, or equipment impedance is given on one MVA and kV base but your study uses a different common base.
Enter Base Values
Formula Summary
Zpu,new = Zpu,old × (MVAnew ÷ MVAold) × (kVold ÷ kVnew)2
Zbase = kVLL2 ÷ MVA3φ
Ibase = MVA3φ × 1000 ÷ (√3 × kVLL)
Example
An impedance of 0.10 pu on a 50 MVA, 13.8 kV base becomes 0.20 pu on a 100 MVA, 13.8 kV base.
Assumptions
The MVA values are total three-phase bases and voltage is line-to-line. Base voltages on opposite sides of a transformer should follow the transformer ratio.
A base conversion changes the numerical per-unit value, not the physical impedance.
Common Mistakes
- Mixing single-phase and three-phase base quantities.
- Using line-to-neutral voltage where line-to-line voltage is expected.
- Adding per-unit impedances before converting them to a common base.
- Changing voltage base across a transformer without following the winding ratio.
Reference Notes
These are standard per-unit base-conversion relationships for balanced three-phase power-system studies. Confirm base definitions and transformer voltage bases before combining impedances.