Transformer

Transformer is an electric device used for conveying AC power by induction from one circuit to another, with original frequency. Normally you change the voltage at the same time (except for the isolation transformer, where the voltage does not change).

Transformer is build of 2 or more coils (windings) wounded on a common magnetic core. Core is usually made of magnetically permeable material. Transformer have  a primary winding and a secondary Winding which are  separated. In autotransformer the primary and secondary winding are connected.

When the primary winding is connected to an alternating voltage source U1, it will sail alternating electric current. This will result in the induction of alternating magnetic field, which penetrates through the other coil it produces - as a result of electromagnetic induction, - the variable electromotive force.

The electromotive force (SEM) is a source of alternating voltage U2 at the output of the transformer.

A major application of transformers is to increase voltage before transmitting electrical energy over long distances through wires. Wires have resistance and so dissipate electrical energy at a rate proportional to the square of the current through the wire. By transforming electrical power to a high-voltage (and therefore low-current) form for transmission and back. Transformers are also used extensively in electronic products to step down the supply voltage to a level suitable for the low voltage circuits they contain. The transformer also electrically isolates the end user from contact with the supply voltage. We used it in TV, power station’s.

Efficiency of transformer dependent loss on core and loss on wire’s

Up we have equivalent circuit, with loses on elements of transformer

Rr- core

Jxg- main winding

Jx1- primary winding reactance

R1- primary winding resistance

Jx2’- second winding reactance

R2`- second winding resistance.

Efficiency = $\frac{\text{Power}\ \text{output}}{\text{Power}\ \text{input}} = \frac{\text{Pwy}}{\text{Pwe}}\ $x 100

Power input = (Power output + copper loss + core loss)