Transformer Calculator: Turns Ratio, Primary and Secondary Current
Enter the transformer kVA rating and primary and secondary voltages. You get the turns ratio, full-load currents on both sides and, if you give primary turns, the secondary turns.
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Turns ratio
9.583 : 1
Step-down- Primary current
- 4.348 A
- Secondary current
- 41.667 A
- Secondary turns
- 52.2 turns
Ideal transformer; real units have a few percent loss and voltage drop.
Show working
- a = 230 ÷ 24 = 9.5833
- Ip = 1,000 ÷ (230) = 4.348 A
- Is = 1,000 ÷ (24) = 41.667 A
- Ns = 500 × 24 ÷ 230 = 52.17
How to use
- Choose single- or three-phase.
- Enter kVA rating and primary and secondary voltage.
- Optionally enter primary turns to get secondary turns.
Good to know
For an ideal transformer, Vp ÷ Vs = Np ÷ Ns = Is ÷ Ip. Full-load current: single-phase I = VA ÷ V; three-phase I = VA ÷ (√3 × line voltage). A 1 kVA 230/24 V transformer carries 4.35 A on the primary and 41.7 A on the secondary.
For three-phase transformers, the ratio shown is between line voltages. Actual turns per winding depend on the star or delta connection on each side (for example an 11 kV/433 V Dyn11 distribution transformer).
Real transformers have losses and regulation, so the secondary voltage drops a few percent at full load and the no-load voltage is slightly higher. Size cables and fuses from these full-load currents with proper margins.
Questions
What is the current of a 100 kVA transformer at 433 V?
100,000 ÷ (1.732 × 433) = 133 A per phase on the LV side.
What is the turns ratio of 230 V to 12 V?
230 ÷ 12 = 19.17 : 1.
Does a step-down transformer increase current?
Yes. Power stays about the same, so lower voltage means higher current on the secondary.
How many secondary turns for 24 V if primary is 500 turns at 230 V?
500 × 24 ÷ 230 = 52 turns (plus a few for losses in practice).
Is this for an ideal transformer?
Yes. Real units have losses and a few percent voltage drop at load.