This simulator is a single-phase transformer with five controls: primary voltage, turns ratio, kVA rating, load and efficiency. The schematic shows the primary and secondary blocks with their voltages and currents, coils on a laminated core, and flux particles moving through the core. Change the ratio to see a step-down become a step-up, and watch current move in the opposite direction to voltage.
• A schematic with a primary block, a secondary block and a core between them, each labeled with live voltage and current. • Five sliders: primary voltage (120-4,160 V), turns ratio (1:1-20:1), kVA rating (5-1,000 kVA), load (0-150 percent) and efficiency (85-99.5 percent). • Readout tiles for primary voltage, secondary voltage, output power in kW, losses in kW and efficiency. • Expandable notes on turns ratio, voltage and current trade-off, core flux, efficiency and losses, with formulas and a worked example.
Secondary voltage is the primary voltage divided by the turns ratio. Current at each winding is the kVA rating converted to VA, divided by that winding's voltage, and scaled by the load percentage. Output power is the loaded kVA times the efficiency, and losses are the difference between loaded kVA and output power. Because the same kVA flows at both windings, a winding at one quarter of the voltage carries four times the current.
A transformer with more turns on the primary than the secondary steps voltage down and current up, which is how a 480 V feeder becomes 120 V at a panel. The reverse arrangement steps voltage up and current down, which is why generator step-up transformers and transmission lines use high voltage to keep current and conductor losses low. The kVA rating limits the current a transformer can deliver at its voltage before it overheats; the load slider runs to 150 percent so you can see what overload looks like.
The primary-to-secondary voltage ratio equals the primary-to-secondary turns ratio. With 480 V on the primary and a 4:1 ratio, the secondary voltage is 480 divided by 4, or 120 V. The simulator divides the primary voltage by the ratio slider value to get the secondary voltage.
A transformer passes nearly the same apparent power from primary to secondary, apart from losses. If voltage falls by a factor of four, current must rise by about a factor of four to carry the same kVA. The simulator computes each current from the kVA rating, the load percentage and that winding's voltage.
Real transformers convert a small part of their throughput to heat through core losses and winding resistance. The efficiency slider sets the fraction of loaded kVA delivered as output kW, and the losses tile shows the remainder. It is a single efficiency value, not a separate core-loss and copper-loss model.
It is an ideal, single-phase teaching model. It does not model power factor, impedance and voltage regulation, inrush current, saturation, three-phase connections, taps or temperature rise. See the Three-Phase Transformer and Power Transformer labs for more detailed equipment models.