Electrical transformers are used to "transform" voltage from one level to another, usually from a higher voltage to a lower voltage. They do this by applying the principle of magnetic induction between coils to convert voltage and/or current levels.
In this way, electrical transformers are a passive device which transforms alternating current (otherwise known as "AC") electric energy from one circuit into another through electromagnetic induction. An electrical transformer normally consists of a ferromagnetic core and two or more coils called "windings". A changing current in the primary winding creates an alternating magnetic field in the core. In turn, the core multiplies this field and couples the most of the flux through the secondary tranformer windings. This in turn induces alternating voltage (or emf) in each of the secondary coils.
Electrical transformers can be configured as either a single-phase or a three-phase configuration. There are several important specifications to specify when searching for electrical transformers. These include: maximum secondary voltage rating, maximum secondary current rating, maximum power rating, and output type. An electrical transformer may provide more than one secondary voltage value. The Rated Power is the sum of the VA (Volts x Amps) for all of the secondary windings. Output choices include AC or DC. For Alternating Current waveform output, voltage the values are typically given in RMS values. Consult manufacturer for waveform options. For direct current secondary voltage output, consult manufacturer for type of rectification.
Cores can be constructed as either a toroidal or laminated. Toroidal units typically have copper wire wrapped around a cylindrical core so the magnetic flux, which occurs within the coil, doesn't leak out, the coil efficiency is good, and the magnetic flux has little influence on other components. Laminated refers to the laminated-steel cores. These steel laminations are insulated with a nonconducting material, such as varnish, and then formed into a core that reduce electrical losses. There are many types. These include autotransformer, control, current, distribution, general-purpose, instrument, isolation, potential (voltage), power, step-up, and step-down. Mountings include chassis mount, dish or disk mount, enclosure or free standing, h frame, and PCB mount.