How Three Phase Electricity works – The basics explained

hey there guys Paul here from the
engineering mindset .com in this video we’re going to be looking at Three phase
electricity and this follows on from our series on Electrical Engineering so if
you haven’t watched the previous videos on this so far then please do this first
links are in the video description below coming up we’re going to be looking at
how a simple AC generator works then we’ll look at a single phase power then
two phase power and then finally three phase power as well as how three phase
power is used and why also while we don’t use four five six phase etc power
so first of all let’s start with a simple AC generator we’ll start with a
single phase to understand what’s happening and then we’ll add in other
phases until we get two three phases let’s take a copper wire and wrap it
into two coils and then place these coils or perceive each other within a
stator and connect the ends together to create a complete circuit now if we
place a magnet in between these coils and we start to rotate the magnet then
the magnetic field will disturb the free electrons within the copper wire and an
electrical current will begin to flow we’ve covered how the free electrons
flow in a previous video on the electricity basics so please check that
out if you’ve not done so already links are in the video description below as
the magnet rotates so does the polarity of the magnetic field as you can see in
the illustration the North and South Pole of the magnet are rotating and as
they rotate they pass across the coils which force electrons to move notice the
lines of the magnetic field are in these oval shapes on each side and they meet
through the central axis of the magnet you can think of these as one side being
positive and the other side being negative and in between these overalls
the magnetic field is neutral you can see that the intensity of the magnetic
field increases on either side until the center where it is at is maximum
strength and then it decreases again until it gets back to the neutral point
so as this field rotates through the coil the coil will experience an
increasing intensity of the magnetic cause positive half and during this
increase the free electrons within the copper coil will be pushed and begin to
move faster and faster in one direction up until it reaches the maximum point of
the magnetic field then as the magnetic field decreases the flow of electrons
will begin to slow all the way until it reaches a neutral point where no
electrons will flow then comes a negative side of the magnetic field and
as this passes through it’s going to pull the free electrons backwards the
game the flow of electrons will flow faster and faster up until the maximum
point of the magnetic field and then it will decrease back to the neutral point
this is why AC electricity is called alternating current because the current
of electrons alternates in direction backwards and forwards just like the
tide of the sea if we were to plot on the graph the speed of the electrons
flowing during the rotation then we would get a sine wave pattern in this
sine wave you can see that the electrons are stationary at the start in the
neutral zone and then the speed increases through the positive half all
the way up to the maximum and then it begins to decrease all the way back down
to the neutral where no electrons will flow again after this comes a negative
half where the electrons speed up to the maximum point and then they begin to
slow down again until the magnet has completed one full rotation where this
will then repeat this complete rotation is known as a cycle and the number of
cycles per second is called the frequency which is measured in Hertz
you’ve probably seen 50 Hertz or 60 Hertz written on your electrical goods
this means that the generator of the power station is completing a full
rotation either 50 or 60 times per second so the direction of the current
is therefore also changing 50 or 60 tones per second also when it is written
on electrical products this is just telling the user what type of
electricity the product should be connected to now coming back to the sine
wave that we saw earlier this product of current also represents power and if we
connect a lamp into the circuit we’ll see that it will increase in brightness
all the way to the peak that maximum point then it decreases in brightness
all the way down until the neutral point where the lamp is actually
off because no current is flowing but then it will increase in brightness
again as a negative half of the cycle comes fruit and the electrons start to
flow back through in the opposite direction and tell again it reaches the
neutral point so at these points in the cycle the lamp is not producing any
light and at these points in the cycle the lamp is not very bright so it’s not
of much use so if you’re working in a room and this lighting is flickering
like this it’s going to get really annoying to improve this we can add
another set of coils or a second phase into the generator we can do this by
placing the coils a hundred and twenty degrees rotation from the first set of
coils and then connect this up to another lamp this rotation means that
the coils will experience the changing intensity of the magnetic field at
different points in time the first coil reaches maximum current and brightness
and as it decreases the second coil will begin to increase this has improved the
lighting for there’s still a gap which will cause a flicker so we can add in a
third set of coils or a third phase and this will mean that one of the lamps are
almost always at its maximum brightness so the lighting is nearly constant there
are still some small gaps between the phases and you could keep adding more
and more phases to fill these gaps but this will become more and more expensive
to keep running all these cables so three phase became widely accepted as it’s a
good compromise between power provided and cost to build now in the real world
you’re not going to use three different lamps on different phases to create
lighting the lamps in your homes are all on single phase but they are flickering
it’s just that they are turning on and off so fast that the human eye can’t see
it unless you record the lamp in slow motion a more practical application is
the power electrical induction motors and other commercial and industrial
equipment as three phase will provide a lot more power to these items meaning
you can pump water higher or you can run motors faster etc etc power is generally
generated and distributed in three phase and transformers are used to change the
voltage if you want to learn how transformers work we’ve also
covered that two links are in the video description below now one of the
interesting things with three phase power is that you can connect all three phases
and power large industrial equipment or you can also connect to only one of the
phases and also power small electrical goods this is generally how large tower
blocks and skyscrapers distribute electricity through the building the
lift motors and air conditioning pumps etc will need three-phase power but the
computers and office equipment will need single-phase power so they distribute
three phase power up the building and then draw off from this as needed the
same occurs with the distribution of electricity across a city houses will be
connected to only a single phase because they do not require much power whereas a
large building will be connected to a three phase supply as they will require a
lot of power okay guys that’s it for this video thank you very much for
watching I hope this has helped you and you’ve enjoyed it if so then please
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