hardware//electronics//component//electrical transformer
An electrical transformer is a device that changes an alternating voltage to a higher or lower one by electromagnetic induction, with two coils wound on a shared iron core and no electrical connection between them, and it is what lets the grid carry power at hundreds of kilovolts and deliver it at 230 V. Phone chargers, welding machines and the substation at the end of a street are all built around one.
An electrical transformer is a device that changes an alternating voltage to a higher or lower one by electromagnetic induction, with two coils wound on a shared iron core and no electrical connection between them, and it is what lets the grid carry power at hundreds of kilovolts and deliver it at 230 V. Phone chargers, welding machines and the substation at the end of a street are all built around one.
The mechanism is induction in two steps. The alternating current in the first coil, the primary, makes a magnetic flux in the core that rises and falls fifty times a second; the core guides almost all of that flux through the second coil, the secondary, where the changing flux induces a voltage. Every turn of either coil sees the same flux, so the voltage per turn is the same on both sides, and the voltages are in the ratio of the turns:
VsVp=NsNp.\frac{V_s}{V_p} = \frac{N_s}{N_p} .VpVs=NpNs.
A secondary with ten times the turns gives ten times the voltage. Energy is conserved, so the current goes the other way: ten times the voltage comes with a tenth of the current, and the power in equals the power out, minus the losses.
More turns, more volts, fewer amperes.
The transformer trades voltage for current at almost no cost, and that trade is what makes long-distance transmission affordable, because the heat lost in a line depends on the current squared.
The losses are small and known. Large power transformers reach efficiencies above 99 %; what is lost is heat in the copper of the windings (Joule heating) and in the core, where the alternating flux both drives eddy currents (hence the core is built of thin insulated sheets) and wastes a little energy remagnetising the iron each cycle.
It does nothing with direct current. A steady current makes a steady flux, which induces no voltage, so a transformer on a battery only heats its primary.
The coils are also an isolation barrier: the secondary has no wire connection to the primary, which is why a transformer can separate a safe low-voltage circuit from the mains.