Full Load Current Turns Ratio calculator for Transformer
Compute transformer full-load current for single/three-phase and find turns ratio a = Np/Ns = Vp/Vs = Is/Ip. Includes examples and quick reference tables.
full load current calculator transformer
Rated kVA, voltage give full-load current: single-phase I = S/V, three-phase I = S/ ( sqrt 3 VLL ). Is/Ip connects the primary and secondary currents in an ideal transformer with the turns ratio a = Vp/ Vs.
Formula & Table Summary:
- Turns ratio (ideal): a = Np/Ns = Vp/Vs = Is/Ip
- Single-phase FLA: I = S / V
- Three-phase FLA: I = S / (√3 × V_LL)
- Rearrangements: S = V × I (1φ), S = √3 × V_LL × I (3φ)
- Current scaling: Is = a × Ip, Ip = Is/a
transformer turns ratio calculator
This calculator determines transformer full-load current (FLA) on primary and secondary and compares them using the turns ratio. In a single-phase unit, full-load current is I = S/V. For a three-phase unit, I = S/(√3·V_LL). The ratio of the turns is a = Np/Ns = Vp/Vs = Is/Ip (ideal transformer), and therefore current is inversely proportional to voltage. Give rated kVA, voltage(s), and system phase to obtain Ip FL and Is FL immediately, and refer currents and impedances across sides with a to. Always use nameplate information and comply with the following standard protection size as specified by your code and coordination study.
single phase transformer FLA
| S (kVA) | Vp (V_LL) | Vs (V_LL) | a | Ip_FL (A) | Is_FL (A) |
|---|---|---|---|---|---|
| 100 | 11000 | 415 | 26.506 | 5.25 | 139.20 |
| 500 | 13800 | 480 | 28.750 | 20.93 | 601.04 |
| S (kVA) | Vp (V) | Vs (V) | a | Ip_FL (A) | Is_FL (A) |
|---|---|---|---|---|---|
| 25 | 2400 | 240 | 10.000 | 10.42 | 104.17 |
Frequently Asked Questions - Full Load Current Turns Ratio calculator for Transformer:
How do I calculate transformer full-load current?
Single-phase: I=S/V. Three-phase: I=S/(√3·V_LL).
What is the turns ratio formula?
a = Np/Ns = Vp/Vs = Is/Ip for an ideal transformer.
How are primary and secondary currents related?
Is = a·Ip and Ip = Is/a, inverse to the voltage ratio.
Does frequency change full-load current?
For a given kVA and voltage, FLA formulas are unchanged; frequency affects design limits, not the algebra.
How do I get kVA from amps?
Single-phase: S=V·I. Three-phase: S=√3·V_LL·I (kVA by ÷1000).
Can I use line-to-neutral voltage?
Use V_LL for 3φ formulas. If using V_phase, compute per-phase and multiply by 3.
What about transformer efficiency and regulation?
They slightly change real currents under load; use nameplate kVA/voltage for FLA and protection sizing.
How do I refer currents between sides?
Multiply/divide by a: I'primary-side = I_secondary/a, etc.
Is inrush current the same as FLA?
No. Inrush is a transient many times FLA and not used for continuous rating.
How precise should results be?
Two decimals are typical; always verify against nameplate and protection coordination.
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