In this post, I will explain how transformers work. Thanks to transformers, it is possible to transmit electric energy in alternating current over long distances, receiving a voltage level and transmitting another level.
Working principle
A transformer consists of two coils linked by a core made of blades of ferromagnetic material.
The primary coil receives current and creates a magnetic field.
Since the coil receives an alternating current, the magnetic flux changes direction and intensity constantly.
The magnetic flux generated in the primary coil goes through the nucleus and arrives in the secondary coil. Since the flux is variable, there is an induced voltage in the secondary coil’s terminals.
The equation of Faraday’s Induction Law tells that the average value of induced voltage depends on the number of turns N and the magnetic flux’s variation speed \frac{\partial \phi }{\partial t}.
\varepsilon_{m} =-N \frac{\partial \phi }{\partial t}
The relation between the voltages E and the number of turns in the primary and secondary.
\frac{E_{p}}{E_{s}}=\frac{N_{p}}{N_{s}}
Why is the transformer’s nucleus is in blades and not a massive block? The magnetic flux’s variation creates an induced voltage in the ferromagnetic nucleus and creates a current called Foucault’s current. This current in a massive block, which has a great area, causes a great power loss because the conductor has a very low resistance and a big area, which produces a big current, which produces a magnetic field that disrupts the flux.
To reduce this parasite current, the nucleus must be divided into blades and insulate one from another to reduce this effect, this way many small currents are generated in blades, and the loss is lower. The insulation between the blades is usually made of varnish or an oxide layer.
Commercials transformers
Coils and a nucleus aren’t enough to make a transformer. A power transformer generates too much heat because the current is very high, therefore it needs to have a refrigeration system, usually with oil. The nucleus and the coils stay immersed in the oil.
The cooling tubes by side serve to heat exchange, the hotter oil goes to the top, enters the tubes above and loses heat, and goes to the bottom part. more above, we have terminals with porcelain insulators. Many transformers have an oil tank to accommodate the oil volume exchange in the thermal convection.
