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Monday, 9 February 2015

Transformers

transformr

Electromagnetic transformers are static devices that starting from an alternating voltage connected to its input, other than the previous gain in the transformer output voltage varying alternating. And allow to provide an adequate tension to the receiver characteristics. They are also essential for transporting electricity over long distances at high voltages, with minimal losses and moderate conductive sections.

Consist essentially of a closed magnetic circuit on which two windings, so that both windings are crossed by the same magnetic flux are wound. The magnetic circuit is constituted (for industrial frequency of 50 Hz) of steel sheets stacked little thickness, to prevent eddy currents.

Winding where the input current is connected is called the primary, and the winding where the payload is connected, is called secondary. The alternating current flowing through the primary winding magnetizing the core alternately. And the secondary winding is traversed by a variable magnetic flux in an approximately sinusoidal flux variation and this engenders by Lenz's law, an alternating voltage in said winding.

FUNDAMENTAL EQUATIONS

The effective value of the electromotive force in the windings of the transformer is determined by the following formulas:



U1 = 4.44 BM A f n1

U2 = 4.44 BM A f n2

Where:

U1 = voltage at the primary winding (volts)

U2 = voltage in the secondary winding (volts)

BM = maximum value of the flux density in the core (Tesla). (In magnetic iron core transformer usually has a maximum value of 1.4 Tesla)

f = frequency of the alternating current (Hz)

n1 = number of turns of the primary winding (dimensionless)

n2 = number of turns of the secondary winding (dimensionless)

A = cross sectional area of the magnetic core (m2)



If the primary and secondary are traversed by the same maximal induction BM & A section of the core remains constant, then;

U1 / U2 = n1 / n2

This ratio is called transformation ratio, and indicates the relationship between input and output voltage, when the transformer is idling, or unloaded, in the secondary.