Transformer

A transformer is an electrical device with no moving parts that transfers energy from one electrical circuit to another by means of magnetic coupling. It works only with an alternating current, i.e. one that periodically reverses. An ideal transformer has perfect magnetic coupling, so that all the power fed into the device is available at its output. In practice there are losses.

A transformer has at least two coils or windings. As current flows through the powered winding, or primary, the winding produces a magnetic field that grows through the unpowered windings. As the magnetic field passes the unpowered winding(s), or secondaries, it causes current to flow in them. As the current changes direction, the direction of the magnetic field and electric flow reverse, causing the same effect in reverse. The changing magnetic field induces mechanical forces that causes the parts of the transformer to vibrate, which is why transformers hum.

The winding with fewer turns of wire has higher current, at a lower voltage. The winding with more turns of wire has less current, at a higher voltage. The ratio of voltages is proportional to the ratio of the numbers of turns of wire. For example, a 5-to-1 step-down transformer might take 1200 volt 60 Hz alternating current, and change it to the 240 volt alternating current distributed to houses. It might have 500 turns of wire on the primary, and 100 turns on the secondary. Many electronic appliances have several secondaries to produce different voltages needed in the appliance.

The high-current low-voltage windings have fewer turns of thicker wire. The thicker wire helps carry more current. The high-voltage, low current windings have more turns of thinner wire. The thinner wire carries less curent, but at a higher voltage.

Some transformers have equal numbers of windings on both coils. These "isolation" transformers are used to prevent direct current flow between electric circuits, while transferring power.

Uses of transformers

Small transformers are often used to isolate and link different parts of radios. See electronics and impedance match.

Some transformers are designed so that one winding turns or slides, while the other remains stationary. These can pass power or radio signals from a stationary mounting to a turning mechanism, such as a machine tool head or radar antenna.

Some moving transformers are precisely constructed in order to measure distances. Most often, they have several primaries, and electronic ciruits measure the shape of the wave in the different secondaries.

Transformers often have silicon steel cores to channel the magnetic field. This keeps the field more concentrated around the wires, so that the transformer is more efficient. The core also keeps the field from being wasted in nearby pieces of metal.

Cores are often made of many stamped pieces of thin steel. This prevents eddy currents from forming in the cores and wasting power by heating the core. Some cores are made of nonconductive magnetic materials, various chemically pure compounds of rust called "ferrite".

High-frequency transformers in low-power circuits where moderate losses are acceptable may have air cores. These save weight and cost.

Power transformers are usually more than 98% efficient. The higher voltage transformers are bathed in nonconductive oil that's stable at high temperatures. These used to be polychlorinated biphenyls, the famous toxic waste, "PCB". Nowadays, nontoxic very stable fluorinated hydrocarbons should be used. The oil cools the transformer, and helps prevent shorts. It has to be stable at high temperatures so that a small short or arc will not cause a breakdown or fire.

"Transformers" is also the name of a line of toys produced by Hasbro, and the cartoon series and movie spinoffs from them.

In the cartoon storyline, a Transformer is a robot that is able to reconfigure itself into the form of a more common and innocuous machine, such as a car or an airplane; the toys had the tagline "More than meets the eye" to reflect this ability for disguise. There were originally two main factions of Transformer, the Autobots and the Decepticons, and they were engaged in a war for the control of their home planet Cybertron. Lacking energy (in the form of "energon"), the Autobots' leader, Optimus Prime sent a mission into space aboard a ship called the "Ark". They encountered an asteroid field, and there the ship was attacked and boarded by the Decepticons, lead by Megatron. The ship was damaged and crashed into Earth, laying dormant until the year 1984.