How 3 Phase Power works: why 3 phases?
Summary
TLDRThis script explores the generation and distribution of AC power, highlighting the role of electrical generators in producing three-phase electricity. It explains how mechanical energy is converted into electrical energy, the significance of different voltages and frequencies used globally, and the impact on household outlets. The script delves into the physics behind the rotation of magnets and wire coils to generate sine waves, the concept of single-phase versus three-phase power, and the practical applications in powering homes and industries. It also touches on the importance of transformers in adjusting voltage levels for efficient power transmission and the calculation of root mean square voltage for measuring AC power.
Takeaways
- 🔌 Outlets provide 120 volts AC at 60 Hz, but other countries use different voltages and frequencies.
- ⚙️ Electrical generators at power stations produce three-phase AC electricity, which is more efficient than single-phase.
- 🧲 The generator's rotor shaft, with a magnet attached, rotates to produce a changing magnetic field that induces a sine wave in the stator's coils.
- 💡 LEDs can demonstrate the direction of current flow in AC, illuminating in sequence as the magnetic field changes.
- 🏡 Home outlets provide either 50 or 60 Hz, meaning the sine wave repeats 50 or 60 times per second.
- 🔄 By adjusting the coil and magnet configuration, the speed of the generator and thus the frequency of the AC can be controlled.
- 🔗 Three-phase systems provide a more constant output power compared to single-phase, which is beneficial for heavy industrial use.
- 🔵 The phase difference in three-phase systems is 120°, which allows for even spacing of the sine waves and efficient power distribution.
- 🌐 Different countries have different standards for voltage and frequency, leading to variations in how electricity is distributed and used.
- ⚡ The voltage provided by outlets is RMS (root mean square), which is a measure that represents the effective value of AC and is used by multimeters.
Q & A
What is the function of an electrical generator?
-An electrical generator converts mechanical energy into electrical energy, typically producing three-phase AC electricity.
What is a single-phase 60 Hz sine wave?
-A single-phase 60 Hz sine wave is a type of alternating current (AC) where the voltage varies in a smooth, continuous cycle 60 times per second.
How does the rotation of a magnet in a generator produce electricity?
-The rotation of a magnet in a generator produces electricity by creating a changing magnetic field that induces a current in the surrounding coils of wire.
What is meant by 'three-phase AC electricity'?
-Three-phase AC electricity refers to an electrical system where three separate sine waves occur at slightly different times on three different wires, providing a more constant output power.
Why are LEDs used in the demonstration of alternating current direction?
-LEDs are used in the demonstration of alternating current direction because they only allow current to flow in one direction, which helps to show the forward and backward flow of current in a sine wave.
How does the frequency of an AC power source affect the magnet's rotation speed?
-The frequency of an AC power source determines how many times the sine wave repeats per second, which in turn affects how many times the magnet must rotate per minute to achieve that frequency.
What is the significance of the 120° spacing between the coils in a three-phase generator?
-The 120° spacing between the coils in a three-phase generator ensures that the sine waves produced by each coil are evenly spaced, providing a balanced and more constant output power.
Why do most homes receive single-phase connections instead of three-phase?
-Most homes receive single-phase connections because they generally require less power and have fewer appliances to power, making single-phase connections sufficient and more cost-effective.
What is the difference between a Y connection and a Delta connection in a three-phase system?
-In a Y connection, the loads connect to a neutral point, providing a lower voltage across each phase and allowing for a neutral wire. In a Delta connection, the loads connect across two phases directly, which can deliver more power but is typically used for balanced loads only.
How is the root mean square (RMS) voltage calculated, and why is it important?
-The RMS voltage is calculated by squaring the instantaneous voltage values to make them all positive, summing them, taking the mean, and then taking the square root. It is important because it represents the effective voltage that produces the same amount of heat in a resistor as a DC voltage of the same value, allowing for accurate power calculations.
Outlines
🔌 Understanding AC Power Generation and Single-Phase Electricity
This paragraph explains the basics of alternating current (AC) power generation and the concept of single-phase electricity. It describes how an electrical generator at a power station converts mechanical energy into electrical energy, typically producing three-phase AC electricity. The paragraph details the components of a basic generator, including the stator, rotor, and three separate coils of wire. It also explains how the rotation of a magnet within the generator creates a magnetic field that induces a sine wave in the coils, resulting in alternating current. The use of LEDs to demonstrate the direction of current flow in a sine wave is mentioned, and the concept of outlets providing a constant voltage despite the alternating current is introduced. The paragraph concludes with a discussion on how the speed of the magnet's rotation can affect the frequency of the sine wave, and how extending the coil or adding another magnet can alter the frequency and voltage of the generated electricity.
⚙️ The Evolution to Three-Phase Electricity and Its Benefits
This paragraph delves into the transition from single-phase to three-phase electricity and the advantages of the latter. It describes how adding additional coils to the stator at 120° intervals creates multiple sine waves that are out of phase with each other, leading to a more constant output power. The paragraph explains the concept of even spacing of sine waves and how moving the coil to different angles affects the sine wave's position. It also touches on the practical limitations of adding more than three phases due to increased complexity and cost. The discussion continues with how different countries have adopted various voltages, frequencies, and distribution designs, leading to a lack of standardization. The paragraph also covers the practical aspects of connecting three-phase systems, such as the use of Y and Delta configurations, and their impact on power delivery and load balancing. The benefits of three-phase systems for powering larger equipment and appliances are highlighted, emphasizing the efficiency and consistency they provide compared to single-phase systems.
🌐 Global Variations in Electrical Systems and the Role of Transformers
This paragraph addresses the global variations in electrical systems, including voltage and frequency standards, and the role of transformers in managing these variations. It explains how transformers are used to step up voltage for long-distance transmission and step down voltage for local distribution. The paragraph discusses the different voltage standards in various regions, such as the UK, Europe, and North America, and how these standards affect the design of electrical systems in residential and commercial properties. It also covers the concept of root mean square (RMS) voltage and how it relates to the peak voltage, which is crucial for calculating power and understanding the performance of electrical devices. The paragraph concludes with a brief mention of how electrical engineering involves complex mathematics and the importance of learning by doing, with a plug for the sponsor, Brilliant, which offers interactive lessons in various fields, including electrical engineering.
Mindmap
Keywords
💡Alternating Current (AC)
💡Generator
💡Three-phase Electricity
💡Sine Wave
💡Stator and Rotor
💡Neutral Wire
💡RMS Voltage
💡Transformer
💡Delta and Y Configurations
💡Frequency (Hz)
Highlights
An outlet provides 120 volts alternating current with a single-phase 60 Hz sine wave.
Different countries use varying voltages and frequencies for AC power.
Electrical generators at power stations convert mechanical energy into three-phase AC electricity.
A basic generator consists of a stator, a rotor shaft with a magnet, and three wire coils.
The rotating magnetic field induces a sine wave in the wire coils.
LEDs can demonstrate the unidirectional flow of current in AC sine waves.
The magnet's rotation creates a single-phase alternating current with a repeating sine wave.
Home outlets provide either 50 or 60 hertz, meaning the sine wave repeats 50 or 60 times per second.
The speed of the magnet's rotation can be adjusted to achieve the desired frequency.
Adding more coils and magnets can reduce the time for the magnetic field to rotate past the coil.
Three-phase electricity is produced by coils placed 120° apart, providing a more constant output power.
The current direction in a three-phase system can be observed using LEDs with opposite polarities.
The voltage in a three-phase system is more constant compared to single-phase.
Countries have different standards for voltage, frequency, and distribution design.
Three-phase systems can be connected in either Y or Delta configurations, each with different applications.
Residential properties typically receive single-phase connections, while commercial properties may have three-phase.
Three-phase systems allow for more balanced power distribution and can handle more appliances.
The voltage and frequency of outlets vary worldwide, with the RMS voltage being a constant value measured by multimeters.
The peak voltage can be calculated using a formula, and the instantaneous voltage can be found from the peak voltage.
The root mean square (RMS) voltage is used to calculate the effective value of AC voltage for practical applications.
Brilliant.org offers interactive lessons in maths, data analysis, programming, and AI for engineering skills development.
Transcripts
sponsored by brilliant this Outlet
provides 120 volts alternating current
if we connect an oscilloscope we find a
singlephase 60 HZ sine wave other
countries use different voltages and
frequencies the AC power is produced by
the electrical generator at the power
station which is some distance away a
generator just converts mechanical
energy into electrical energy typically
they will produce three-phase AC
electricity meaning it outputs three
separate sine waves which all occur at
slightly different times on three
different wires inside a basic generator
we find the main housing or stator and
then in the center is a magnet which is
attached to the rotor shaft we then
Place three separate coils of wire
within the stator the rotor shaft
attaches to basically anything that
rotates when the shaft rotates the
magnet will rotate and this causes the
magnetic field to also rotate the
magnetic field will then pass through
each of the coils at a different time if
I rotate this magnet past this coil of
wire we can see it produces a sine wave
the magnetic field interacts with the
electrons in the wire and forces them to
move imagine the North Pole is pushing
them away and the South Pole is pulling
them back the electrons are alternating
their Direction forwards and backwards
to to prove this we can use LEDs because
LEDs only allow current to flow in One
Direction so by connecting two LEDs in
opposite directions we can tell which
direction current is Flowing but normal
speed it's a little hard to see but in
slow motion we can clearly see that only
one LED illuminates at a time so the
current is definitely flowing forwards
and backwards in the sine wave the
magnet in our generator rotates and
pushes electrons forwards and then pulls
them backwards this will create a
singlephase alternating current with a
sine wave which repeats every time the
magnet makes a full rotation past the
coil the outlets in our homes provide
either 50 or 60 hertz meaning the sine
wave repeats 50 or 60 times per second
to achieve that the magnet needs to
rotate thousands of times per minute
however we can reduce the speed by
extending the co
and adding another magnet because that
will reduce the time taken for the North
and South Pole to rotate past the coil
we can also use gearboxes to increase
the rotational speed but for now we will
stick to a basic model so we have a
singlephase generator the voltage will
start at zero then increase up to the
peak positive value and then decrease
back to zero then on the negative half
the value will increase to the Peak
negative value and again decrease back
to zero this is what the sine wave is
representing notice this value changes
but the voltage at the outlet is
constant I'll explain why later on in
the video we can use this to power a
load like a lamp the lamp will increase
in brightness as the current alternates
with the sine wave as a side note if you
use the slow motion feature on your
smartphone you can see an incandescent
lamp flicker because of the AC current
but it's too fast for the human eye to
see however most lights are now led
which are usually constant so you
probably won't be able to see these
flicker if we look at the output power
of this generator we can see it's not
constant because of the sine wave if we
added another separate coil to the
stator and positioned this 120° away
then the coil will experience the change
in magnetic field at a different time to
the first coil the voltage generated by
the coil will increase and decrease at a
different time so the sine wave will be
delayed this gives us two phases we can
see this will improve the output power
but there's still a gap we can add
another separate coil 120° from the
second coil and this will also
experience the changing magnetic field
at a different time to the other coils
and this gives us three phases we can
see this gives us us a much more
constant output power the current is
flowing back and forth in each phase we
can prove that with this small
three-phase generator and some LEDs we
arranged the LEDs in pairs of opposite
polarities so that only one will
illuminate at any time depending on the
direction of the current in the wire we
can see they are Illuminating and in
slow motion we can clearly see the
current is alternating Direction the
coils in the generator are placed
120° apart simply because that gives us
even spacing of the sine waves that are
produced we can move the coil to any
angle but the sine wave will also move
and we won't have equal spacing by the
way you can download my Excel sheet and
see how the angle changes as well as the
instantaneous phase voltages links down
below for that we could add a fourth
phase a fifth phase or a sixth phase but
the generator becomes more and more
complex and expensive we would also need
more cables more control and protection
equipment complex transmission and
distribution infrastructure more complex
Transformers and Motors Etc it's then
harder to balance the electrical Network
and it's very hard to synchronize
generators to work together so we
instead settled on three phase for
generators and Equipment perfect oh but
unfortunately each country decided to
use a different voltage different
frequency and a different distribution
design great notice on our generator we
have three coils but six wires these
could all connect to individual loads
but notice the sign wave changes from
positive to negative at different times
so the current flows at different times
this means we could join the ends of the
coils and the ends of the loads together
that allows us to use just three wires
which is a lot cheaper the current will
flow back and forth on whichever phase
happens to be going that way we can see
on the three-phase current waveform at
for example
180° phase a has Z amps flowing phase B
has positive current and phase C has
equal negative current flowing this
works great for equal three-phase loads
but with this design we can only connect
across two phases so the voltage will be
very high we can't use this to power our
Outlets because it will just destroy our
appliances but if we reconfigure this
into a y connection then we can run a
neutral wire from the center point back
to the center of the generator we can
also connect this point to ground
meaning that this point in the system is
0 volts if the current is balanced on
All Phases then no current will flow on
the neutral however if one phase
increases to say 30 amps then 20 amps
will flow on the neutral the neutral
will carry the difference back to the
generator or Transformer to keep the
system balanced because we now have a
neutral we can connect across just one
phase and neutral this gives us single
phase we're basically just connecting
across one coil of the generator or
Transformer we can do that on each phase
or we can connect to three phases for
larger equipment like Motors this
connects across two coils but the phases
occur at different times so the voltage
isn't quite double it's just the
difference between the two sine waves we
can either connect the three phases in y
or Delta configuration there are
different reasons but basically if the
loads were the same resistance or
impedance and the phase t-phase voltage
was also the same the current would be
larger in a Delta configuration because
the loads connect across two phases
whereas the Y connected loads connect to
a zero point so they experience
different voltages the Delta can deliver
much more power but it can only Power
balanced three-phase loads if you need a
neutral then we need to use a y
configuration by the way I have made
these cool mugs with the three-phase
basic formulas on and there's also a PDF
guide links down below if you'd like one
each power station generates three
phases a Transformer increases the
voltage to hundreds of thousands of
volts this keeps the current and energy
loss is low over the long transmission
distance when it reaches a city it
enters another Transformer which reduces
the voltage and distributes this on the
sub transmission lines these might feed
large industrial or commercial customers
but it otherwise continues to a
distribution substation where the
voltage is gain reduced and distributed
along the streets to the properties
typically Residential Properties are
provided singlephase connections and
Commercial properties have three-phase
connections although some parts of the
world do provide three phases to homes
homes generally need less power because
they have less stuff to power so a
singlephase connection is usually fine
we can also convert single phase into
three phase using a rotary converter if
we connect too many appliances to a
single phase we will overload the
circuit and trip the breaker three phase
allows us to distribute the power so
that we can connect more appliances a
three-phase heater will use more energy
than a singlephase version but it
produces more heat so it does more work
the heat is also consistent unlike the
pulsating singlephase version we could
use smaller heaters to get the same heat
output with three phases we can connect
three heaters to the single phase but
they will all pulse at the same time the
same with electrical motors imagine
three phase as three people taking turns
to rotate the wheel instead of just one
it's a smoother rotation and is easier
to maintain momentum the voltage and
frequency of the outlets in the
properties vary around the world the
multimeter shows a constant voltage
value but the voltage is actually
varying significantly we can see that in
the sine withd this constant value is
the RMS voltage which is lower than the
peak voltage we can easily find the peak
voltage using this formula if we know
the peak voltage then we can easily
calculate the instantaneous voltage
using this formula the sine wave has
equal positive and negative values for
voltage and current if we added these
all together we get zero so we need a
different way to calculate this someone
realized that if we connected a DC
voltage to a resistor It produced heat
and they could calculate this power then
they applied an ac voltage and they kept
increasing the peak voltage Until It
produced the same amount of heat the DC
voltage was around 70% of the peak ac
voltage so they did some complex maths
and found that if they squared the
instantaneous voltages to turn them all
positive then added them all together
and took the mean value value then
squared that value they got the same ac
voltage as the DC voltage they called
this the root mean squar voltage and
that is what our multimeter calculates
instead of showing a constantly changing
value the local distribution transformer
is designed to provide different
voltages around the world depending on
the local regulations in the UK and
Europe properties are typically provided
230 Volt singlephase or 400 vol three
phase which will also provide 230 bolt
single phase in North America domestic
properties are typically provided 240
volt single phase for large appliances
or they can connect to half of that to
get20 volt for smaller appliances small
commercial properties might be provided
208v 3phase which also provides 120 volt
single phase larger properties might
receive 480 volt three-phase and 277
volt single phase this will power large
equipment and then another Transformer
will reduce this down to 208 volt 3phase
120 volt singlephase when it's needed we
can also then convert singlephase AC
into DC using a rectifier but that's a
topic for another video electrical
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