Fundamental Physics/Electricity/Transformer

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Transformer3d col3.svg

TRANSFORMER is a static device which simply steps-up or steps-down the voltage,or current without changing the supply frequency. (An isolation transformer does not change the voltage except for losses.)

Transformers are used, as an example, because the generation of electricity is at very high voltage and consumption is at very low voltages, so in order to maintain these requirements we use transformers. High voltage is used in transmission of power to keep current down, because losses due to wire resistance increase with the current.

Transformer stands for "the thing which coverts."

Let us now assume that there are Np turns on the primary side and Ns on the secondary side.

(An isolation transformer has the same number of turns on the two sides. Isolation transformers are used to present a barrier to low frequency or direct current power, while passing AC or higher frequency power.)

Let us also assume we have connected the generating station side wires to the primary side. We are connecting the load across the secondary side.

We can say that the two windings over the transformer core are nothing but inductors. Flux is emitted from the coil which is excited(the primary side).

The flux lines travel through the less susceptible (magnetically resistive) iron core and a few lines travel through air (leakage in electrical terms). So the flux lines which travel through the core excite the secondary coil. If we neglect loss and leakage, the voltage and current in side of the transformer will represent the same power, i.e., power equals voltage times current. So if the voltage is stepped down, current will be stepped up, and vice–versa if the voltage is stepped up.

In an ideal transformer (no losses or leakage) the voltage ratio, output/input, is the turns ratio, i.e, Ns divided by Np.

Transformer construction and operation[edit]

Transformer3d col3.svg

Let vs and v_p be output and input voltage . We can see that transformer provide

Voltage step up (voltage amplification) if vp > vs or Np > Ns
Voltage step down (voltage attenuation) if vp < vs or Np < Ns
Voltage buffer (voltage conduction) if vp = vs or Np = Ns


Impedance matching[edit]

See also[edit]