Single-phase transformer
Curvo Studio

Current model·Electromagnetic induction

Single-phase transformer

Observe how alternating magnetic flux transfers energy from the primary winding to the secondary winding.
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Primary windingSecondary windingLaminated coreMagnetic flux
Turns ratio0.1 N₂/N₁
Secondary voltage0 V
Secondary current0 A
Core flux density0 T
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Induction experiment

Voltage and magnetic flux waveforms

Change turns, frequency and load to observe the induced secondary voltage and core flux.

Live winding valuesApply power to generate the curves
Primary and secondary voltageTwo AC cycles with individual normalized amplitudes
PrimarySecondary
010203040+10−1Time (ms)Normalized voltageApply power to generate the curves
Core magnetic flux densityFlux lags the applied voltage by approximately 90°
Bmax 0 T
010203040+10−1Time (ms)Flux densityApply power to generate the curves

What is a single-phase transformer?

Working principle

A transformer transfers electrical energy between two circuits using a shared magnetic field, with no electrical connection between them. Alternating current in the primary winding sets up an alternating flux in the laminated iron core; that flux links the secondary winding and induces a voltage in it according to Faraday's law. Because the mechanism relies on a changing flux, a transformer works only on AC — connect one to DC and the primary is simply a low-resistance short circuit.

Turns ratio and impedance

Voltage is transformed in proportion to the turns ratio, and current in inverse proportion, so an ideal transformer neither creates nor destroys power. A 10:1 step-down transformer gives one tenth of the voltage and can supply ten times the current. Impedance is transformed by the square of the turns ratio, which is why transformers are also used for impedance matching in audio and radio-frequency circuits rather than only for changing voltage.

Losses and efficiency

Real transformers lose energy in two places. Copper losses are the resistive losses in the windings and rise with the square of the load current. Iron losses — hysteresis and eddy currents in the core — depend on flux and frequency and are essentially constant whenever the transformer is energised, which is why laminated, grain-oriented steel is used. Efficiency peaks where the two are equal and typically reaches 95–99 % in a well-designed unit.

Where it is used

Transformers make the AC grid possible: generation at medium voltage, transmission at hundreds of kilovolts to keep line current and losses low, then stepping back down for distribution and household use. Smaller single-phase transformers appear in power supplies, isolation and safety applications, welding sets, doorbells and audio equipment. Isolation transformers with a 1:1 ratio provide no voltage change at all — their whole purpose is safety and noise separation.

Frequently asked questions

How do you calculate the turns ratio and secondary voltage of a transformer?
For an ideal transformer, Vs / Vp = Ns / Np, and the currents scale the other way, Is / Ip = Np / Ns. With 500 primary and 50 secondary turns on 230 V, the secondary gives about 23 V. Real transformers give slightly less under load because of winding resistance and leakage flux, which the simulator shows through the coupling coefficient and load.
Why does a transformer only work with alternating current?
A transformer needs a changing magnetic flux to induce voltage in the secondary (Faraday's law). DC creates a constant flux, so no secondary voltage appears once it settles, and the primary current is limited only by the small winding resistance, which can overheat the winding and saturate the core.
What happens if a transformer is run at a lower frequency than it was designed for?
For a given voltage the core flux is inversely proportional to frequency (V ≈ 4.44 × f × N × Φ). Running a 50 Hz design at a lower frequency with the same voltage pushes the core into saturation, and the magnetizing current and heating rise sharply. The simulator warns about core saturation as you lower the frequency.
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