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Transformer




Why do we use transformers? />
Electrical energy has losses by transmitting current. It depends on the magnitude of the current. To keep the losses as low as possible we use higher voltage (Þlower current). This process is done with a transformer.



Main parts
The transformer consists of two main parts: the iron core and the windings.

The iron core is made up of laminations, which have low losses and are insulated from each other to prevent eddy current losses.

The windings usually consist of copper wire, which is insulated to prevent short circuits.




Principle of transformation

The magnetic flux in the primary winding induces a magnetic field in the secondary winding. The field depends on the frequency and the magnitude of the flux and the turns in the secondary winding.

If the secondary winding has twice as many turns as the primary winding, the voltage doubles (E1:E2 = N1:N2 .E - voltage, N - turns) and the current is just the half (I1*N1 = I2*N2 .I - current).



Electric power
Electric power is the product of I*E. If we eliminate the number of turns, we will get this equation: E1*I1 = E2*I2. The power you need on the secondary side is equal to the power applied on the primary side.

When power is transferred from winding to the other, losses arise. These losses are known as the iron or copper losses.




Leakage flux
When a transformer is loaded, current flows in both windings. Every current carrying conductor produces a magnetic field, which encircles the conductor. A winding, which consists of several individual conductors, therefore produces a leakage flux. The leakage flux causes a reactance voltage drop in both windings (primary and secondary). In addition, a resistance voltage drop also occurs in both windings. The reactance and the resistance together are called the impedance.





Single-phase transformer

This transformer consists of a yoke, an iron core and two windings. The windings are wound around the same limb and they are called primary and secondary winding. A transformer has losses because the voltage induces in the iron eddy currents. They can be kept small by using thin laminated sheets that insulate the iron from each other.







































Three - phase transformers
The three - phase transformer is used for energy distributions. This transformer consists of three limbs, connected together by top and bottom yokes. Each limb is carrying a primary and a secondary winding. These windings can be connected in star or delta.

Generally the transformers are classified by their power rating. There are small, distribution and large transformers:

Small transformers are dry-type transformers. They are used to step down the system voltage for particular applications. Transformers which have separate windings are used to prevent direct contact with dangerous voltage.

Distribution transformers are used to increase and reduce the a.c. voltage of primary distribution systems. They are usually filled with a liquid cooling and insulating medium.




loss - Verlust


magnitude - Größe


eddy current - Wirbelstrom


magnetic flux - magnetische Fluss


insulate - isolieren




conductor - Leiter


voltage drop - Spannungsabfall


leakage flux - Streufluss


winding - Spule

iron core - Eisenkern

 
 
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