every day we use dozens of
electrical and electronic devices and many times these require a transformer which although generally
we don't give much importance is the component that allows us to use electricity in a more controlled way since if we connect our devices directly to a socket we will not have good results and even more, these same components make it possible to obtain in our home electricity that was probably generated
tens of kilometers away in general terms a transformer is made up of two or more coils of different characteristics components that as we saw
in a previous chapter are capable of generating a magnetic field
when a current passes through them and also induce a current when they are affected
by a varying magnetic field understanding this, a transformer is simply made up
of a primary winding which when receiving an alternating current induces a continuously varying magnetic field and a secondary winding that when interacting
with the magnetic field of the primary winding induces an alternating current output the main result of the configuration is that
we can reduce or increase the output voltage depending on how are built the two coils in addition to allowing us
to reduce considerably energy losses when we transmit electricity over long distances But there is much more than that in this chapter we will see
how a transformer works but first I want to thank PCBWay
for sponsoring this chapter PCBWay offers a wide range of products including standard and advanced PCBs flexible printed circuits assembly, templates and PCB design and also when registering you will get
a voucher for five dollars with which they can buy their first 10 PCBs
completely free so take a look at their website www.PCBWay.es first of all we must understand why the transformers work with alternating current and not with direct current this occurs due to the Faraday's Law which in simple terms tells us that in order
to induce a current in a conductor the magnetic field must be changing over time
either increasing or decreasing therefore if we use direct current the primary winding will generate a magnetic field that will eventually stop growing and be constant over time and as a consequence the secondary winding
is only going to induce a current at first but once the magnetic field is constant it will simply stop inducing a current understanding this, let's analyze a transformer
closer to reality During this video we will focus on a
shell-type transformer consisting of a laminated core with three columns whose coils are wound on the central column the position of the coils is a little different
to what we had seen before but remember that as long as the magnetic field from the primary winding reaches the secondary winding everything will work basically the same for now let's just focus on the coils later we will focus on the laminated core in this particular case the primary coil
is the one located in the center while the secondary coil,
with higher voltage is located outside for security reasons since is preferable to keep it far away from the core
to avoid contact one of the main characteristics, depending
of the application in which we use the transformer is the transformation ratio
between primary and secondary winding that is, how much larger or smaller is the output voltage with respect to the input voltage this relationship mainly depends on the difference between the number of turns of the two coils although for simplicity, suppose that the quantity in the primary winding is going to be constant if by adding a single turn we will be inducing
a small output voltage by adding a second turn we will obtain twice the voltage since basically we will be connecting
two voltage sources in series exactly like when we put
several batteries in series in this way, if we have fewer turns in the secondary coil than in the primary coil the output voltage will be lower if the number of turns is the same,
the voltage will be the same and if the number of turns is greater,
the voltage will be higher it's a pretty simple relationship in fact we can apply it in reverse Well, if we know the input voltage
and the output voltage we could estimate the relationship between
the number of turns and furthermore, in addition to the voltage,
the current output will also vary but in reverse an easy way to remember this
is resorting to the law of conservation of energy if the voltage increases,
somewhere we have to be losing specifically this conservation occurs
when we calculate the nominal power of each coil the nominal power, which is measured in watts,
equals voltage times current therefore the only way that power stay constant and the voltage is increased at the same time,
is reducing the current which also directly affects another
characteristic of transformers that is the diameter of the cables
used on each coil because by reducing the current we can
use thinner cables without worrying about these melting in theory we could use the same diameter but remember that less material means:
less weight, more compact sizes and obviously less cost of materials
for the companies that produce them which is even more important when we are talking
about high voltage transformers so there's no point in making the wires
bigger than necessary this same difference in diameters means that
in case we have a transformer in which we do not know which terminal
corresponds to which coil since they are generally covered we could measure both resistances and deduce that the one that is smaller
corresponds to the coil with the fewest turns since, as we saw in the chapter on resistors a greater cross-sectional area and a smaller
length means less resistance now getting back to the topic
of energy conservation in an ideal world the energy delivered
by the primary winding would be equal to that received
by the secondary winding however in the real world this is not so,
because there are multiple losses as losses in the transfer of the magnetic flux voltage drops in conductors
that make up the coil and heat losses among others and it is precisely to solve these problems
that a core is used in transformers being the material that composes it the determining factor in the effect it will produce this due to a fundamental characteristic of the materials known as magnetic permeability and that in simple terms indicates
the capacity of each material to affect and be affected
by a magnetic field to get an idea, just by changing
an air core for a steel core the magnetic flux that will pass
through the steel sections it will be between 2000 and 6000 times stronger
than with the air core with which we will increase considerably
the induced current in the secondary coil although keep in mind that regardless
how high is the core permeability we will never get as a result
an output power greater than the input because there phenomenon
known as magnetic saturation in which, beyond a certain limit
magnetization of materials it keeps getting harder to increase it further So far it sounds pretty good
since we increase the magnetic flux however when using a core
we will meet new problems the first of them are stray currents,
Eddy's currents or Foucault's currents a steel core in addition to having high magnetic permeability is a conductive material and even when it is
electrically isolated from windings the magnetic field of the primary coil
is going to induce currents in the core just like it does on the secondary coil of course these currents are not going anywhere because we are talking about a metal block
which forms a closed circuit but still the electrons are going to be flowing inside and as we have already mentioned above,
a current generates a magnetic field which by the way, according to Lenz's law is going to oppose the magnetic field that generated it in the first place in a nutshell these stray currents are going to be negatively affecting
the efficiency of our transformer but we can still do something to control them and in fact the solution is quite simple if we don't want there to be currents in the core the easiest way to stop them
is putting up a resistance literally look for a material
that have at the same time high magnetic permeability
and a high coefficient of resistivity one of the most commonly used solutions are the steel sheets with small
silicon percentages, around 4% which are also electrically isolated from each other that is, not only does the material have
a higher coefficient of resistivity but also its design of sheets
decrease cross section which is another variable that increases
the resistance of a component in short, we reduced as much as we could
the stray currents although it should be noted that in this process, by opposing a resistance to the movement of currents an increase in the temperature of the material
will be generated and in fact, the higher the
oscillation frequencies of the magnetic field the greater the losses will be the second problem we will encounter is that the amount of the magnetic flux
present in the core depends not only on the amount of current
applied to inductors at any given time but also from the magnetic flux
that previously existed in the core this property is known as hysteresis and we could understand it as an inertia of the core when changing the direction of its magnetic flux or an energy expense
that we must make for it to reorient luckily the steel and silicon cores also have hysteresis losses
much smaller than a common steel core which is why they are ideal for a
large number of applications in addition to being relatively cheap to produce however they have a high density, which causes an increase in the weight of the transformers and also when working with frequencies that exceed hundreds of thousands of Hertz Stray current losses and the temperature
generated as a result of their dissipation exceed acceptable limits for applications requiring a high-frequency
alternating current source there are other materials such as ferrite,
which is a non-conductive ferrous ceramic material that is, it is not affected by stray currents
no matter how high the frequencies are in addition to being less dense than steel however they usually have
lower magnetic permeability all this information is for reference only because there are several alloys
with different amounts of each element and therefore different magnetic permeabilities, resistivity coefficients density, hysteresis effects
and of course also different costs that is, there is no core that works for all contexts in fact there may be cases where
we don't even want to use a core like in tesla coils after having talked about all these problems and different losses that occur in a transformer surely you must be thinking that they should not
be very efficient in transferring energy from primary coil to secondary coil however these manage to reach
efficiencies greater than 95% an extremely high value compared to energy transfer in mechanical systems where the friction between the parts
generates much greater losses but, as I mentioned at the beginning of the video transformers not only play a role
in energy transformation to be able to use it on different devices they are also extremely important
to transmit power over long distances which by the way has a close relationship
with an epic battle Between Thomas Edison and Nikola Tesla and how we end up using
alternating current around the world but clearly that will be a topic
for a next chapter if you consider the work I do to be worthwhile remember that you can support me through PATREON
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