Transformers alone cannot do the following:
- Convert DC to AC or vice versa
- Change the voltage or current of DC
- Change the AC supply frequency.
However, transformers are components of the systems that perform all these functions.
Energy losses An ideal transformer would have no losses, and would therefore be 100% efficient. In practice, energy is dissipated due both to the resistance of the windings known as copper loss or I2R loss, and to magnetic effects primarily attributable to the core (known as iron loss). Transformers are, in general, highly efficient: large power transformers (over 50 MVA) may attain an efficiency as high as 99.75%. Small transformers, such as a plug-in "power brick" used to power small consumer electronics, may be less than 85% efficient.
Transformer losses:
- Winding resistance. Current flowing through the windings causes resistive heating of the conductors (I2 R loss). At higher frequencies, skin effect and proximity effect create additional winding resistance and losses.
- Eddy currents. Induced eddy currents circulate within the core, causing resistive heating. Silicon is added to the steel to help in controlling eddy currents. Adding silicon also has the advantage of stopping aging of the electrical steel that was a problem years ago.
- Hysteresis losses. Each time the magnetic field is reversed, a small amount of energy is lost to hysteresis within the magnetic core. The amount of hysteresis is a function of the particular core material.
- Magnetostriction. Magnetic flux in the core causes it to physically expand and contract slightly with the alternating magnetic field (producing a buzzing sound), an effect known as magnetostriction. This in turn causes losses due to frictional heating in susceptible ferromagnetic cores.
- Mechanical losses. In addition to magnetostriction, the alternating magnetic field causes fluctuating electromagnetic forces between the primary and secondary windings. These incite vibrations within nearby metalwork, creating a familiar humming or buzzing noise, and consuming a small amount of power.
- Stray losses. Not all the magnetic field produced by the primary is intercepted by the secondary. A portion of the leakage flux may induce eddy currents within nearby conductive objects, such as the transformer's support structure, and be converted to heat.
- Cooling system. Large power transformers may be equipped with cooling fans, oil pumps or water-cooled heat exchangers designed to remove the heat caused by copper and iron losses. The power used to operate the cooling system is typically considered part of the losses of the transformer.
Losses may be either load-dependent('load-losses') or independent of it ('no-load loss'). Winding resistance dominates load-losses, whereas hysteresis and eddy currents losses contribute to over 99% of the no-load loss.
IV. Find the equivalents to the following.
iron losses
energy losses
winding resistance losses
eddy current losses
hysteresis losses
magnetostriction losses
mechanical losses
stray losses 㳿
cooling system losses
copper loss
V. Find English equivalents to the words:
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