Physics Project On Transformer
Physics Project On Transformer
Physics Project On Transformer
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For safety isolation of your lower voltage AC Supply from the main
power supply.
An ideal transformer is an imaginary transformer which has
In other words, an ideal transformer gives output power exactly equal to the
input power. The efficiency of an idea transformer is 100%. Actually, it is
impossible to have such a transformer in practice, but ideal transformer model
makes problems easier.
Infinite permeability of the core: Higher the permeability, lesser the mmf
required for flux establishment. That means, if permeability is high, less
magnetizing current is required to magnetize the transformer core.
No leakage flux: Leakage flux is a part of magnetic flux which does not get linked
with secondary winding. In an ideal transformer, it is assumed that entire amount
of flux get linked with secondary winding (that is, no leakage flux).
100% efficiency: An ideal transformer does not have any losses like hysteresis
loss, eddy current loss etc. So, the output power of an ideal transformer is exactly
equal to the input power. Hence, 100% efficiency.
Limitations
Transformer Temperature Limitations
For dry (air-cooled) transformers (that normally have their windings insulated with silicone resin), a
temperature limit of 155°C is usually imposed. Allowing air to circulate through the windings and over
the core cools these transformers. Assuming a maximum ambient temperature of 40°C, then the
temperature rise is limited to 155° – 40° = 115°C.
For oil-insulated transformers, there is usually a measurement of oil temperature and winding
temperature provided. The simulated winding temperature is called hot-spot. It is derived by passing
a representative amount of load current through a resistor located in the oil and measuring the resulting
temperature
Current Limits
1. It produces heat in the windings of the transformer as we have just discussed above.
2. It produces a voltage drop across the output winding proportional to the load current. As the
transformer is loaded, the secondary voltage will fall due to the affects of winding resistance
and reactance.
We have previously discussed how the operating voltage and frequency must be kept within rated
values due to the physical design (winding insulation and core construction). The subtle effect of these
parameters on the overheating of the core is sometimes overlooked.
When any transformer is operating at its rated voltage and frequency, it will be operating with its rated
value of flux in the core.
If the voltage rises while the frequency remains constant, or the frequency falls while the voltage
remains constant, the core flux will increase. The core will heat up due to the effects of hysterisis and
eddy currents in the core.
Typical magnetization curve for a transformer core; Figure 6 (right) Relationship between core flux and
core heating
A voltage increase of 10% above the rated value will give a flux level of 10% above its rated value. From
Figure 5, it can be seen that, if the flux level is 10% above normal, the iron has commenced to saturate.
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