How 3 Phase Power works: why 3 phases?

Summary

This 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

00:00

🔌 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.

05:01

⚙️ 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.

10:02

🌐 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.

Keywords

💡Alternating Current (AC)

Alternating Current (AC) is a type of electrical current where the flow of electric charge periodically reverses direction. In the video, AC is explained as the standard form of electricity delivered to homes and businesses. The video demonstrates how AC is produced by electrical generators and how its frequency, such as 50 or 60 Hz, determines how many times the current alternates per second.

💡Generator

A generator is a device that converts mechanical energy into electrical energy, primarily by rotating a magnet inside a coil of wire. The video describes how generators produce AC electricity by creating a magnetic field that passes through wire coils, generating sine waves of electrical current. The role of the generator in power stations is central to the production and distribution of electricity.

💡Three-phase Electricity

Three-phase electricity refers to a system where three separate sine waves of electricity are generated and transmitted, each offset by 120 degrees. The video illustrates how this system allows for more constant power output compared to single-phase electricity. It also shows how three-phase systems are widely used for industrial and commercial power distribution due to their efficiency.

💡Sine Wave

A sine wave is a smooth, repetitive oscillation that represents the alternating voltage and current in AC electricity. The video explains how the sine wave characterizes the rise and fall of voltage in both single-phase and three-phase systems, demonstrating the repeating pattern of electrical flow that occurs in these systems.

💡Stator and Rotor

The stator is the stationary part of a generator, while the rotor is the rotating part. The video explains how the rotor, attached to a rotating magnet, interacts with the stator's coils to generate electricity. As the rotor spins, it induces a magnetic field in the stator, creating the electrical current needed for power generation.

💡Neutral Wire

The neutral wire is a conductor that carries the difference in current between phases back to the power source. The video highlights its role in balancing electrical systems, especially in three-phase configurations. In a 'Y' connection, the neutral wire is used to safely return current to the generator, helping maintain system stability.

💡RMS Voltage

Root Mean Square (RMS) voltage is the effective value of an alternating current voltage, equivalent to a direct current (DC) voltage that produces the same amount of heat in a resistor. The video discusses how RMS voltage is lower than the peak voltage in an AC sine wave and explains its importance in measuring the usable voltage provided to consumers.

💡Transformer

A transformer is an electrical device that changes the voltage of an AC current, typically increasing it for long-distance transmission or decreasing it for local distribution. The video shows how transformers are essential in the power grid, stepping up voltage to reduce energy loss over distances and stepping it down to safe levels for homes and businesses.

💡Delta and Y Configurations

Delta and Y (wye) configurations are two methods for connecting electrical loads to three-phase systems. In the video, the Delta configuration is shown to connect loads across two phases, providing more power, while the Y configuration connects loads to a central neutral point, making it suitable for systems requiring a neutral wire and more balanced load distribution.

💡Frequency (Hz)

Frequency, measured in hertz (Hz), refers to the number of cycles per second in an AC sine wave. The video discusses how different countries use different frequencies, typically 50 or 60 Hz, and how this affects the electrical power systems in homes and businesses. The generator’s rotational speed determines the frequency of the produced AC.

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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