hi gone transmitting power in DC or
direct current can have great advantages
over AC or alternating current
oh yeah I did try to show you DC was
better by electrocuting those animals if
it wasn't for that meddling Tesla and
his stupid ways now we would be living
in a much better world of DC power line
Edison you didn't know why AC was better
back then and don't know why BC can be
better now so shut up
in fact even I didn't know of these
so-called high-voltage DC power lines
until I heard this guy talk about them
these cables are direct current cables
not alternating current great science
channel check him out I was like is this
a joke or some special experiments but
then I did some in-depth research and
realize that nope it's real like I said
in my previous video Edison was
transmitting 120 volt DC to homes from
the source which would mean huge
currents through the transmission power
lines that would limit the transmission
distance to a kilometer or two the key
success to Tesla's AC was that using
transformers for the same power he could
easily bump up the AC voltage way high
and in return dropped the current way
low and that would minimize the power
loss over the wire resistance for very
long transmission distances then after
the transmission we would just drop it
back down to 120 volt AC using
transformers to distribute between homes
as needed if changing the DC voltage
level was as easy as AC we would just
stick with DC why let me show you some
of the benefits number one every power
line is equivalent to series resistors
and inductors of the wire and parallel
stray capacitance between the power
lines or line to ground the longer the
power line is the more of these
components are added something like this
inductor and capacitor this is a filter
if I try to measure the AC output using
my the power line straight capacitors
don't blow up like that let me just run
it on low voltage AC I have a 1 volt 10
kilohertz running through my inductor
and if I connect the capacitor to the
output you see that at this frequency
the output is attenuated and phase
shifted by 180 degrees the impedance of
the inductor grows by the increase of
frequency while for the
passes or it drops so the inductor tries
to block the AC while the capacitor
tries to short it to ground same thing
on the power lines the AC gradually gets
attenuated to a point that over a great
distance almost no energy gets to the
other side but for DC there is none of
that impedance nonsense at zero Hertz DC
the inductor impedance is zero and the
capacitor impedance is infinite so all
the current that goes in comes out of
the other side untouched only the wire
resistance wastes power
same as AC that's why in AC power lines
they keep them well above ground and far
apart to reduce those stray capacitances
but in some cases where we need to run
the power under the salt water of the
sea say between United Kingdom and
Europe or underground in the cities the
line to earth capacitance becomes huge
sucking so much AC power because the
wire is right beside earth or water this
will waste a lot of active and reactive
power where DC doesn't have any problem
whatsoever
number 2 DC only transmits active power
and there is no reactive power unlike in
AC C in an AC system the total or
apparent power is a complex number made
of two components the first one is real
or active power in watts that actually
does the work the other part is reactive
power which doesn't do any more can
these due to the inductances and
capacitances in the circuit let me show
you here I have my unloaded microwave
transformer connected to 120 volt AC and
if I measure the current going in it's
around five and a half amps although I'm
not powering anything from it WTF it's
because I'm placing the Transformers
primary inductor with around 22 ohm
impedance on 120 volt AC so it draws
current here I'm also measuring the
current using a shunt the current in
green looks a bit ugly due to the ion
core if you see here the current and
voltage are ninety degrees out of phase
power is the product of voltage and
current when that product is positive we
have a positive power which means that
we are sucking power from the source and
when that product is negative we have
negative power which means that we are
pushing power back into the power lines
so in pure inductors and capacitors
where there is 90
agrees between voltage and current the
amount of positive and negative powers
is equal which means the net active
power usage is zero and we only have
reactive power now although the reactive
power is not a waste the current draw
exists and wastes power over all the
wire resistances imagine you have to
send two amps to do something that only
needs one amp
that's four times the power loss over
wire resistance my wires and transformer
are getting warm as we speak with no
output such nonsense doesn't exist in DC
where we only draw active power only the
needed current is transmitted number
three is the skin effect as I've
mentioned before if you look at the
cross-section of a wire for a see the
current is pushed to the surface of the
conductor due to the electromagnetic
fields the higher the frequency the
thinner the skin becomes this reduces
the useable wire and increases its
resistance and so more waste of power
what DC uses the entire cross section
which means with the same wire we waste
less and can transmit more power skin
effect line inductance and capacitance
and reactive power draw waste tons of
power on AC transmission lines where in
high-voltage DC we waste 30 to 40
percent less power
number 4 DC lines are much easier to
connect to each other unlike AC let's
connect to AC lines together here I have
my car inverter running on the 12 volt
battery and here I have the city power
line both of them are exactly at 120
volt AC that and that's why you don't
try that at home being 120 volt AC is
not enough see the sine wave is coming
from the city and the square wave is
coming from the inverter they are not
the same shape and they are not in phase
because their frequencies are slightly
different that creates huge voltage
differences to connect them they must be
the same shape same frequency same phase
same voltage level same background same
ethnicity and graduated from the same
school but for DC we just need to make
sure the voltage levels are the same
right now I've rectified the two sources
with a diode and capacitor and we can
easily connect them together yes we need
to make sure they are the same voltage
level and the same polarity of course
and of course if we connect them with
diodes
like this it protects against reverse
polarity and ensures that always the
highest voltage will go to the output so
the voltage levels don't need to be the
same either so considering all these
benefits why don't we use DC all over
the place well I've already told you
it's much harder to convert DC for such
super power high voltage lines at low
voltages converting DC is done very
easily using the new circuits and
transistors like the buck or boost
switching converters but imagine doing
it at 10 kilovolt hundred kilowatts or a
million volts in fact I had to talk to
one of my friends Mike Piner who's a
senior electrical technician in a high
voltage DC transmission station you see
Mike here in his natural habitat among
the huge components needed to chip those
super high voltage DC lines apart he
helped me understand how they convert
such huge voltages the bottom line is
that at least with the current
technology this in-line conversion is
more expensive and requires more
maintenance compared to AC lines that
use transformers especially in urban
areas that you need a power converter
almost every block now let me show you
how to convert AC into DC of course you
know that we can use a puny single diode
rectifier and I'm using a light bulb as
the load and on the scope you can see
that the yellow line is the input sine
wave and the blue is the output of the
diode where the negative of the input is
cut off now to make it a DC all we need
to do is the connected capacitor across
the map I always pick a properly rated
capacitor for your voltages now if I
connect it in you see that the light
goes brighter as the capacitor is
helping to keep the voltage up
discharging between the pulses are
charging with the next positive peak
coming in the capacitor here is doing a
lot of filtering because the AC
component here is pretty large we could
also use a full bridge rectifier instead
I'm using a differential probe here to
measure the output because the input and
output reference voltages are different
here and you see that the bridge is also
flipping the negative wave of the input
up and using it and that's why the light
is at full brightness now if I connect
the capacitor you see that the light
goes even brighter and the ripple
voltage is much smaller because the
peaks are coming that double the
frequency and the voltage doesn't have
time
to drop too far now imagine if we had
three phases so I have to make my own
three phases I had made this contraption
before where I'm using a brushless DC
motor to turn another one as a generator
these motors work with three phases
coming in to turn a permanent magnet and
in Reverse if you turn them they
generate three-phase output here we are
if I run the motor we get three phases
coming out of the other end the
reference point of the three phases is
the center of the resistors between the
phases now we can use a three-phase even
fuller bridge rectifier or EFB are every
phase being more positive than the other
phases feeds the positive line through
the top diodes or being more negative
than the other phases gets fed from the
negative line through the bottom diodes
okay I have my EF BR hooked up to my
three phases let's turn it on see the
blue is the output measured by the
differential Rome because my voltage
levels are smaller the effect of the
diode drop is more significant let me
turn off the three phase voltages the
fascinating thing is that now I have six
positive waves per cycle that add up and
create my output which is already pretty
DC looking without a capacitor now the
AC component is much smaller and higher
frequency and easy to filter when I
connect my capacitor in those high
voltage DC centers they kind of do the
same thing first off there needs to be
three phases coming in then they use a
transformer to bump them super high to
100 kilovolt 250 kilo volt or more they
also use another transformer to shift
those three phases 30 degrees to create
six phase AC then they rectify these six
phases using the mother of all fullness
bridge rectifier or ma FB are also
instead of diodes they use something
called silicon controlled rectifier
which they also call valves they can
open and close these scr's are like
diodes that can be turned on using an
external signal when the voltage across
them is positive
imagine these components have to be huge
so they can withstand a million volts
and carry tons of current rectifying six
phases they get a huge DC voltage with a
smaller ripple voltage at 12 times the
main power frequency much easier to
filter and yet they have to put huge
capacitors and inductors size of a
building to be able to handle the super
high voltage and current Wow that power
plant is like my makeup I could ride
those rectifiers forever too bad they
won't let me in due to liability issues
a bunch of kittens anyway of course
there will be a bunch of power loss
converting AC to high-voltage DC but
then you can transfer it much more
efficiently over continents until it
reaches the next station where you have
to convert it back down to AC to
distribute they use the same kind of
valve circuit and set up to switch the
DC back into AC and through a
transformer and filter to create a
three-phase output of course the created
three phases have to be synchronized
with the existing power system otherwise
explosion that's why they use the
existing three phases to time and switch
those huge valves to make perfect
signals let me show you how to create AC
from DC here I have two switches that
are controlled by the same signal and
switch the DC input to the AC output if
the switches are up they send the
forward voltage out and if they switch
down they send a reverse voltage out so
if it switches back and forth
it creates an AC at the output here I
made the circuit with ad Walpole twelfth
row switch and if I switch it I can
create AC and if I make two more of
these and switch them 120 degrees out of
phase I can make three phase signals and
filter them into a nice sine wave now we
just need to hire a bunch of underpaid
workers to switch these at sixty Hertz
high voltage DC lines are currently used
for backbone power transmission only but
maybe in the future the technology
lowers the cost and increases the
reliability of DC conversion so that we
can use DC all over the place as I
always intended get out