Transformer Efficiency & Turns Ratio Calculator
Calculate transformer turns ratio, voltage transformation, current transformation, and efficiency for any AC transformer.
Transformer Guide
Transformer Basics
A transformer is two coils (windings) sharing a magnetic core. Alternating current in the primary creates a changing magnetic field, which induces an EMF in the secondary. Only works with AC — DC produces no changing field, so no induction. Turns ratio: N_p / N_s. Determines voltage ratio. Voltage ratio: V_p / V_s = N_p / N_s. Current ratio (ideal): I_p / I_s = N_s / N_p (inverse of voltage ratio). Step-up: secondary has more turns than primary. V_s > V_p. Used in: power transmission (generators
Why High-Voltage Transmission
Power transmitted: P = V × I. For given power, doubling V halves I. Resistive loss in cables: P_loss = I²R. Halving I quarters losses. Why pylons carry 132-400 kV: minimises transmission losses across long distances. Substations step down progressively: 400 kV → 132 kV → 33 kV → 11 kV → 400 V (domestic 3-phase) → 230 V (single phase domestic). Each step-down via large transformer. Power station typically produces 11-25 kV initially. Step up to 400 kV for grid distribution. Step down at consumer
Real Transformer Losses
Ideal transformer: 100% efficient. Real transformers: 95-99% for power transformers. 85-95% for small domestic transformers. Losses come from: copper losses (I²R in windings) — depend on load. Iron losses (eddy currents in core + hysteresis) — constant regardless of load. Laminated cores: reduce eddy currents (insulating layers between thin steel sheets). Silicon steel: reduces hysteresis losses. Toroidal cores (donut-shaped): minimal magnetic leakage, higher efficiency. Larger transformers more
Applications
Domestic: every plug-in 'wall wart' adapter contains a transformer (or modern switch-mode equivalent). Steps 230V to 5-12V for electronics. Computer PSUs: combine transformer with rectification and regulation. EV charging: charging stations contain transformers stepping down grid voltage. Welding: massive step-down transformers (240V to ~30V at hundreds of amps). Audio: output transformers in valve amplifiers match speaker impedance. Isolation transformers: 1:1 ratio. Used for safety isolation r
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