Transformer Construction System

Transformer Objec

A transformer is a device that changes ac e lectric power at one voltage level to ac e lectric power at another volt age level through the action of a magnetic fie ld. It consists of two or more coils of wire wrapped around a common ferromagnetic core. These coils are (usually) not directly connected. The onl y connection betwecn the coils is the common magnetic nux present within the core.

One of the transfonner windings is connected to a source of ac electric power, and the second (and perhaps third) transformer winding supplies electric power to loads. 1lle transfonner winding connected to the power source is called the primary winding or input winding, and the winding connected to the loads is called the secondnry winding or output winding. I f there is a third winding on the transformer, it is called the tertiary winding.

Transformer Construction

TIle invention of the transfonner and the concurrent development of ac power sources eliminated forever these restrictions on the range and power level of power systems. A transfonner ideally changes one ac voltage level to another voltage level without affecting the actual power supplied. If a transfonner steps up the voltage level of a circuit, it must decrease the current to keep the power into the device equal to the power out of it. 1llcrefore, ac electric power can be generated at one central location, its voltage stepped up for transmission over long distances at very low losses, and its voltage stepped down again for fmal use. Since the transmission losses in the lines of a power system are proportional to the square of the current in the lines, raising the transmission voltage and reducing the resulting transmission currents by a factor of 10 with transformers reduces power transmission losses by a factor of lOll Without the transfonner, it would simply not be possible to use electric power in many of the ways it is used today.

In a rmx:lern power system, electric power is generated at voltages of 12 to 25 kV. Transfonners step up the voltage to between 110 kV and nearly 1000 kV for transmission over long distances at very low losses. Transfonners then step down the voltage to the 12- to 34.5-kV range for local distribution and fmally pennit the power to be used safely in homes, offices, and factories at voltages as low as 120 V.