Hi friends in this video we are going to
see three-phase AC supply if I consider
a single turn generator it will generate
a voltage which is single-phase AC and
having very less value of voltage if I
want to increase the value of AC voltage
I need to connect more number of turns
in series so that will become armature
winding remember in generator AC voltage
is generated at the armature sometimes
that much of voltage is not even
sufficient to supply three-phase heavy
industrial practical loads at that time
what we can do we can connect such
single-phase supplies in such a manner
that it will give you more power to
supply such a heavy loads here comes the
need of three-phase supply
while we needed three-phase supply
because of voltage produced by a
single-phase supply is very less and
that is not enough to supply practical
industrial loads you must have seen in
industry big machines are there for a
production purpose those machines cannot
work on single-phase supply that we are
having at our house for that we need a
very high voltage which cannot be
provided by single-phase supply so
industrial heavy loads require polyphase
supply what is the meaning of phase
phase means branch or circuit or you can
even say it is winding while poly means
many so obviously I need to connect many
circuits many single-phase circuit such
a way that it will give me high voltage
and high power so what is that in a
polyphase system in polyphase system
there are
many independent AC voltages present
simultaneously
how many that depends upons number of
phases
we will strictly talk in terms of a
three-phase system so what does
three-phase system means obviously it is
a three-phase so three independent AC
voltages will be there but there will be
some relationship between magnitude of
those issue-- voltages frequency of the
same and some phase difference will be
there among them so let's narrate this
so three phase system the magnitudes and
frequencies of AC voltages are same and
a phase difference of 360 degree divided
by three which is nothing but 120 degree
with respect to each other
I repeat so in the three phase system
you will having a three voltages whose
magnitudes and frequencies are same and
there will be a phase difference between
all of them and that phase difference is
120 degree so that is what a three-phase
system is all about why we are studying
a three phase system there are certain
advantages of a three phase system over
single-phase system so let's list out
one by one
the first and most important advantage
is the output of three-phase machine is
always greater than output of
single-phase machine of same size second
advantage transmission of three-phase
power is very much economical as it
needs less copper or less conducting
material as compared to single-phase
power
this is what obvious because we can
raise the voltage in three-phase system
if you transmit the power at high
voltage there will be less core losses
happening which means less conducting
material required therefore we got a
single-phase supply but actually we
generate three-phase supply at the
generating station then three-phase
supply is raised its voltage to the
transformer and then it is transmitted
because of this reason third advantage
rotating magnetic field or you can also
call it as RMF can be generated in
three-phase supply
hence three-phase machines are self
starting
with the help of single-phase supply we
cannot produce RMF that is rotating
magnetic field
hence single-phase machines are not self
started a very important point you must
have seen a single-phase motor in our
house and that is nothing but a fan in a
fan capacitor is provided to provide one
more phase so actually we are having two
phases over there and because of that
whenever we are having more than one
phases rotating magnetic field can be
produced so this is the advantage of a
three-phase supply because three phases
are there so rotating magnetic field can
be produced and because of that no need
to do any arrangement the way we have
done in a single-phase motors next
advantage is suppose I am having a
three-phase supply if I have only two
wires I can get a single-phase supply
meaning three-phase supply give rise to
three single-phase supplies but vice
versa is not possible that means we
cannot obtain three-phase supply from
single-phase supply whereas from
three-phase supply we can get three
single-phase supplies next advantage is
suppose I am converting this three-phase
supply into DC the curve or the DC I
will get is much more smoother than that
of a single-phase supply DC what does
that mean ripple will be very low so
rectifier DC output voltage
is smoother what do you mean by smoother
having less ripple if number of phases
are increased at the supply side so
these are the certain advantages we are
having in three-phase system compared to
single phase system hence it is obvious
that whenever there is a high power
requirement we should go for three-phase
supply thank you
