Transformers Explained - How transformers work

Summary

This educational video explores the inner workings of transformers, essential devices in modern electrical systems that transfer and alter voltage levels. It explains how transformers operate only with alternating current, using coils and an iron core to efficiently step up or step down voltages for various applications, from small devices to entire cities. The script delves into the physics behind transformers, discusses energy losses, and provides a basic understanding of calculations related to transformer operation. Additionally, it touches on the use of transformers in rectifier circuits and the importance of apparent power in transformer ratings.

Takeaways

• ⚡ Transformers are essential devices that transfer electrical energy and are used to change voltage and current levels.
• 🔄 They only work with alternating current (AC), not direct current (DC).
• 🏠 Transformers are found in various sizes, from small ones in doorbells to large ones supplying entire cities.
• 🌀 They consist of two coils of wire wrapped around an iron core, with one coil connected to the power supply (primary side) and the other to the load (secondary side).
• 🔋 Transformers are rated in volt-amps (VA) or kilovolt-amps (kVA), not watts, because they transfer power between coils.
• 🔧 Step-up transformers increase the voltage output, while step-down transformers decrease it, allowing for efficient power transmission over long distances.
• 🌐 By increasing voltage and reducing current, transformers minimize energy losses during transmission.
• 📉 Transformers have efficiency losses due to eddy currents and resistance in the coils, which generate heat and cause the characteristic humming sound.
• 🔧 The efficiency of transformers is enhanced by using laminated iron cores to reduce eddy currents.
• 🔄 Transformers are integral in rectifier circuits to convert AC to DC, with diodes and capacitors smoothing the output.

Q & A

What is the primary function of a transformer?

A transformer is used to transfer electrical energy between two or more circuits through electromagnetic induction. It can change the voltage and current levels, making it essential for transmitting electrical power efficiently.

Why do transformers only work with alternating current (AC) and not with direct current (DC)?

Transformers only work with alternating current because AC generates a changing magnetic field, which induces a voltage in the secondary coil. DC creates a constant magnetic field that does not induce a voltage in the secondary coil, except briefly when the DC is switched on or off.

What units are transformers rated in, and why?

Transformers are rated in volt-amperes (VA) or kilovolt-amperes (kVA) because they transfer apparent power. The actual power (in watts) depends on the efficiency and the load connected to the transformer.

What are the typical applications of small and large transformers?

Small transformers are commonly used in devices like doorbells and laptop chargers. Larger transformers supply power to homes and businesses, while the largest transformers can supply entire regions, towns, or cities.

How does a step-up transformer differ from a step-down transformer?

A step-up transformer increases the voltage on the output side, typically used for long-distance power transmission to reduce energy loss. A step-down transformer decreases the voltage on the output side, used to lower high transmission voltages to safer levels for local distribution and household use.

Why is high voltage used for long-distance power transmission?

High voltage is used for long-distance power transmission to reduce energy losses. Higher voltage reduces the current in the transmission cables, which in turn decreases the energy lost as heat due to the cable's resistance.

What are the key components of a transformer, and how do they function?

The key components of a transformer are two separate coils of wire (primary and secondary) and an iron core. The primary coil receives electrical energy, creating a magnetic field that induces a voltage in the secondary coil, thus transferring the energy.

What causes the humming sound in transformers?

The humming sound in transformers is caused by the vibrations of the iron core. The alternating current causes the core's laminated sheets to expand and contract slightly, creating vibrations and the characteristic humming noise.

What are copper losses and iron losses in transformers?

Copper losses refer to the energy lost due to the resistance in the transformer's wire coils, generating heat. Iron losses are due to eddy currents and hysteresis in the iron core, which also generate heat and reduce efficiency.

How does a transformer improve the efficiency of electrical power transmission?

A transformer improves efficiency by allowing electrical power to be transmitted at high voltages and low currents, reducing energy losses due to the resistance of transmission cables. The voltage is then stepped down to usable levels closer to the point of consumption.

Outlines

00:00

🔌 Introduction to Transformers and Their Applications

This paragraph introduces transformers as essential components in our modern electrical systems, connecting homes to power stations. The script explains that transformers can change voltage and current levels and are rated in volt-amps (VA) or kilovolt-amps (kVA). It highlights the presence of transformers in various forms, from small ones in doorbells and laptop chargers to large ones supplying entire regions. The video is sponsored by Skillshare, offering a one-month free trial to the first 1000 viewers. The paragraph also mentions the construction of transformers, which typically consists of two coils of wire around an iron core, with the primary side connected to the power source and the secondary side connected to the load.

05:03

🌐 Understanding Transformer Operations and Energy Efficiency

This section delves into how transformers operate, focusing on their use with alternating current (AC) and not direct current (DC). It explains the concept of step-up and step-down transformers and their role in energy transmission efficiency. The script discusses the importance of high voltage for reducing energy loss over long distances and the use of transformers to adjust voltage levels accordingly. It also touches on the three-wire system in North America, which allows for 120 or 240-volt options, and contrasts it with the simpler two-wire system used in most of the world. The paragraph further explains the generation of magnetic fields around wires carrying current and how transformers use these fields to induce voltage in secondary coils, with the iron core enhancing efficiency and reducing energy loss.

10:03

🔧 Exploring Transformer Construction and Efficiency

The script continues with an in-depth look at transformer construction, discussing the use of laminated iron sheets to reduce eddy currents and improve efficiency. It also covers the concept of power loss due to resistance in the coils, which generates heat and represents a form of energy loss known as copper losses and iron losses. The paragraph explains the humming sound transformers make due to vibrations caused by the alternating current. It then moves on to describe how the number of wire turns in a transformer affects voltage and current levels, with step-up transformers increasing voltage and decreasing current, and step-down transformers doing the opposite. The concept of volt-amp (VA) as a measure of apparent power is introduced, emphasizing that transformers do not create energy but rather transfer it, maintaining the same power on both sides.

15:06

📚 Transformer Calculations and Practical Examples

This paragraph provides a series of calculations and formulas to understand transformer operation in a more technical manner. It presents hypothetical scenarios involving step-up and step-down transformers, explaining how to calculate input and output voltages, the number of turns on primary and secondary coils, and the currents on both sides of the transformer. The formulas are used to demonstrate how changes in voltage and turns ratio affect the transformer's operation. The script also emphasizes the importance of maintaining the same power on both sides of the transformer, as indicated by the product of voltage and current. Practical examples are given to illustrate these concepts, helping viewers grasp the fundamental principles of transformer calculations.

Keywords

💡Transformer

A transformer is a device used to transfer electrical energy between circuits through electromagnetic induction. In the video, transformers are described as essential for connecting homes to power stations and adjusting voltage levels for efficient power distribution. Examples include transformers used in laptop chargers and those supplying entire cities.

💡Alternating Current (AC)

Alternating Current (AC) is an electric current that reverses direction periodically. Transformers only work with AC, as highlighted in the video, because it allows for the continuous change in magnetic fields needed to transfer power between coils.

💡Primary Coil

The primary coil is the coil in a transformer that is connected to the power source. The video explains that the primary coil receives the initial electrical energy, which is then transferred to the secondary coil. It's a critical component in the function of a transformer.

💡Secondary Coil

The secondary coil is the coil in a transformer that delivers the transformed electrical energy to the load. According to the video, the secondary coil receives power from the primary coil through electromagnetic induction, enabling voltage changes to meet specific requirements.

💡Step-Up Transformer

A step-up transformer increases the voltage from the primary to the secondary coil. The video illustrates its use in transmitting power over long distances, where high voltage and low current reduce energy loss.

💡Step-Down Transformer

A step-down transformer decreases the voltage from the primary to the secondary coil. The video explains its application in reducing high transmission voltages to safer levels for residential and commercial use, such as 240 volts for homes.

💡Voltage

Voltage is the electric potential difference between two points. In the video, voltage is crucial in determining how transformers adjust power levels for efficient transmission and usage, with examples like stepping down from 12,000 volts at power stations to 240 volts for home use.

💡Current

Current is the flow of electric charge. The video highlights the relationship between current and voltage in transformers, explaining that increasing voltage reduces current, which in turn minimizes energy loss during power transmission.

💡Iron Core

An iron core is used in transformers to concentrate the magnetic field and improve efficiency. The video shows that placing an iron core between coils enhances the transformer's performance by guiding the magnetic field more effectively to the secondary coil.

💡Electromotive Force

Electromotive Force (EMF) is the voltage generated by changing magnetic fields. The video explains that transformers rely on EMF to transfer power between coils, as the alternating current creates a varying magnetic field that induces voltage in the secondary coil.

Highlights

Transformers are essential to modern lifestyle, connecting homes to electrical power stations.

Transformers transfer electrical energy and can change voltage and current, but only work with alternating current.

Most appliances are rated in watts or kilowatts, but transformers are rated in volt-amps (VA) or kilovolt-amps (kVA).

Transformers have two coils of wire around an iron core, with the primary side connected to the power supply and the secondary side to the load.

Step-up transformers increase the voltage on the output, while step-down transformers decrease the voltage on the output.

Higher voltage transmission reduces energy loss in cables due to lower current, making it more efficient.

North America uses a three-wire system for 120 or 240 volts, while most of the world uses a simpler two-wire system for 230 volts.

Transformers only work with alternating current because the magnetic field needs to constantly change polarity.

Iron cores in transformers concentrate the magnetic field and improve efficiency, but also cause eddy currents and energy loss.

Transformers are not 100% efficient due to copper losses in the wires and iron losses in the core.

The humming sound from transformers is caused by vibrations in the core due to alternating current.

Step-up transformers have more turns of wire on the secondary side to increase voltage and decrease current.

Step-down transformers have fewer turns of wire on the secondary side to decrease voltage and increase current.

Transformers are rated in VA because they transfer power without knowing the specific load, which affects the true power in kilowatts.

Rectifier circuits use transformers to convert AC to DC by reducing voltage and using diodes and capacitors.

Transcripts

this is a transformer

we find them everywhere they are

essential to our modern lifestyle they

provide the connection between our homes

and the electrical power stations i'm

going to show you how they work why they

make this

noise and also how to calculate them in

this video which is sponsored by

skillshare the first 1000 people to

click the link and join will get a one

month free trial more about that later

transformers look something like this

we find them illustrated with symbols

like these in electrical drawings

transformers are simply a device used to

transfer electrical energy it can change

the voltage and current in the process

which is very useful however they only

work with alternating current they do

not work with direct current most

appliances are rated in watts or

kilowatts but transformers are rated

with the units va for volt amps or even

kilovolt amps we will learn why later on

in this video

we can find small transformers used on

doorbells or laptop chargers we have

larger versions to supply our homes and

businesses and we also find enormous

ones which supply entire regions of

towns and even cities

so where have you seen transformers used

let me know in the comment section down

below

there are lots of different ways to

construct a transformer i have some

small common examples here

but they are essentially just the same

thing

they have two separated coils of wire

wrapped around an iron core

the generator or supply is connected to

one coil known as the primary side and

then the load which is the thing we need

to provide power to

is connected to the other coil and this

is known as the secondary side if i take

this one apart we can see there are

simply two separate coils of wire and

lots of sheets of iron that's it the

transformer is just transferring power

between the coils electricity is

dangerous so do not try this at home

unless you are qualified and competent

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okay so if we use something called a

step up transformer then we can increase

the voltage on the output

if we use a step down transformer then

we can decrease the voltage on the

output but why would we want that well

the power station might be producing 12

000 volts but your home needs between

120 and 240 volts

the power station is probably a long

distance away

so there's going to be a lot of

resistance in the cables resulting in

huge losses of energy on the way

so instead we use a step up transformer

to increase the voltage to around maybe

400 000 volts then as we reach the town

we use a step down transformer to reduce

this back to around 11 000 volts for

local distribution and then we reduce it

again down to around 240 volts for our

homes by increasing the voltage through

a transformer we reduce the current

energy loss in a cable depends on the

electrical current and the resistance of

the cable if this cable has for example

5 ohms of resistance and we try to send

10 kilowatts through it at 240 volts we

would lose about 87

because the current is high but the

voltage is low and so the losses are

huge but if we were to send this at 400

000 volts we'd lose a tiny fraction of

just one percent

because the current is low

so we can transmit power further and

more efficiently at higher voltages

as a side note the reason homes in north

america can have either 120 or 240 volts

is because they use a three wire system

where an additional wire is connected to

the center of the secondary coil

therefore we can use just half of the

coil to get 120 volts or the full coil

to get 240 volts

however most of the world uses around

230 volts and for this they use just a

two wire system which is a much simpler

design and allows more power to the

outlets and this is useful for example

to quickly boil a water kettle by the

way i have covered residential

electrical systems previously in great

detail links down below for that

when we pass an electrical current

through a wire it generates a magnetic

field around the wire

if we reverse the direction of current

the magnetic field also reverses we can

see that by placing some compasses

around the wire

when we connect an ac generator to a

closed loop of wire

the magnetic field inside the generator

is going to basically push and pull the

electrons in the wire

so that they constantly alternate

direction between moving forwards and

backwards

so the magnetic field is therefore

constantly reversing

the voltage is going to vary between his

maximum and minimum values because of

this

that's why we see a sine wave pattern if

we connect an oscilloscope to a power

outlet this pattern repeats 50 or 60

times per second depending on whether

it's a 50 or 60 hertz supply the aec

frequency in north america is 60 hertz

but most of the world is just 50 hertz

with a transformer the frequency we put

in is the frequency we get out we can

just increase or decrease the voltage

not the frequency

when we wrap the wire into a coil this

magnetic field becomes even stronger

the wire has to be insulated with an

enamel coating to ensure the current

flows along the entire length

otherwise it will just take the shortest

route and it will not work

if we place a second coil of wire in

close proximity to the first coil then

the magnetic field will induce a voltage

into this second coil because this

magnetic field is going to push and pull

the electrons in the second coil

forcing them to move

this is therefore a transformer

the same thing happens if we move a

magnet past a coil of wire

the magnet will induce a voltage into

the coil

the key component here is that the

magnetic field is constantly changing

polarity as well as intensity

this disturbs the free electrons and

causes them to move

and we call this electromotive force

however this only works with alternating

current

it will not work if we connect a direct

current supply to the transformer the

flow of electrons will still create a

magnetic field around the primary coil

but this will be constant and a fixed

polarity in intensity

so it will not disturb the electrons in

the secondary side

the only time it will create an

electromotive force using direct current

is briefly when the switch is opened and

closed because this energizes and

de-energizes the magnetic field of the

coil

so it is therefore changing

or alternatively we could change the

voltage

because that will also increase and then

decrease the magnetic field of the coil

notice that when i pass a dc current

through this transformer we get a very

brief voltage spike as the magnetic

field increases

and also as it decreases

but if i use an ac supply we get a

constant output voltage because the

magnetic field is constantly changing

and that is why we use alternating

current now we can just use two separate

coils of wire as a transformer it will

work but not very well the problem is

that we're wasting a lot of the magnetic

field because it's not in range of the

secondary coil so we place a

ferromagnetic iron core between the

coils this concentrates the magnetic

field and guides it to the secondary

coil so that the transformer is more

efficient however this is not a perfect

solution

it will result in eddy currents flowing

around the core which will heat up the

transformer and therefore wastes energy

to reduce this the core is made of lots

of thin laminated sheets

which restricts the eddy current

movements and reduces their effects

although we will still lose some of the

magnetic field due to leakage flux

and we also get some losses due to the

disturbances caused at the joints we

also lose energy in the wire and the

coils because they will always have some

resistance and this generates heat so in

a transformer we have copper losses as

well as iron losses the alternating

current causes the sheets to expand and

contract tiny tiny amounts which causes

vibrations between the sheets and this

is why we get that humming sound

a step up transformer works simply by

having more turns of wire on the

secondary side

this increases the voltage but it

decreases the current a step down

transformer works by having less turns

of wire on the secondary side this

reduces the voltage but increases the

current now this isn't a magical device

that produces more energy than it

receives for example a step down

transformer might receive

240 volts and it outputs 120 volts we

see that the voltage halves

but the current doubles if we multiply

the voltage and current we see the same

value on each side

this is the volt amp value which is

power or apparent power and that has to

remain the same so if the voltage

changes then the current has to change

in proportion to maintain the power so

why do transformers use the units of kva

instead of kilowatts well the

transformer is just transferring power

between the coils so we use the volt amp

unit the kilowatts depend on what you

connect to the transformer the

manufacturer doesn't know what you will

connect to the transformer so they state

the total

rated apparent power in volt amps and

that's because in ac circuits the load

depends on the true power in kilowatts

and the power factor which is basically

efficiency and this varies depending on

the device some energy is consumed but

it produces no work it is just wasted as

heat and we call this reactive power

with the units var power factor is just

the ratio of true power and apparent

power if you think of a glass of beer

the liquid beer is the useful stuff

this is your true power in kilowatts but

there is always some foam which is

useless we don't want that this is the

reactive power or the volt amp reactive

you pay for the total volume of the

glass regardless of how much foam and

beer is inside

this is your apparent power in vault

amps now if you have a good bartender

you will get a little foam and lots of

beer for your money but if you have a

bad bartender then you're going to get

lots of foam and not so much beer for

your money the transformer manufacturer

is basically saying this transformer can

handle a glass this big but it's up to

you how much beer and foam you put into

that the less foam you try to pass

through

the more beer you can get out so the

more efficient the devices that you

connect the more things you can power

transformers are also often used in

rectifier circuits to convert

alternating current into direct current

the transformer first reduces the

voltage and then some diodes convert

this into a rough direct current a

capacitor then smooths this out into a

nice clean power supply you can learn

how that works in detail in our previous

video links down below for that

let's run some basic calculations for

transformers assuming it is perfect with

no losses if we had a transformer with 1

000 turns on the primary and 100 turns

on the secondary and we supplied it with

120 volts

what voltage would we see on the

secondary side we can use this formula

to find that out and we see the answer

is 12 volts so this is a step down

transformer what if we only knew the

output voltage and the amount of turns

well we could find the input voltage

using this formula and if we input the

values we get this answer

if we wanted to find the number of turns

on the secondary side and we knew the

voltages and primary turns then we could

use this formula to get our answer

if we wanted to find the number of turns

on the primary side we could use this

formula and this will give us the answer

if we had a current of 1.2 amps on the

secondary

then we find the primary current using

this formula and we see the answer is

0.12 amps we could also find the answer

if we knew the secondary current and

both voltages by using this formula

if we knew the current on the primary

side and the voltages of the primary and

secondary we could find the secondary

current using this formula

or we could also find the answer by

using this formula

we then check that the power is the same

on both sides of the transformer by

multiplying the voltage and current

let's now consider some step up

transformer examples if we had 100 turns

on the primary and 200 on the secondary

and we supplied it with 120 volts what

voltage would we see on the secondary

well we can use this formula to find

that out so we see the answer is 240

volts so this is therefore a step up

transformer what if we only knew the

output voltage and the amount of turns

well we could find the input voltage

with this formula if we wanted to find

the number of turns on the secondary

side and we knew the voltage and primary

turns then we could use this formula if

we wanted to find the number of turns on

the primary then we could use this

formula

if we had a current of 1 amps on the

secondary then we find the primary

current by using this formula and we see

the answer is 2 amps

we could also find the answer if we knew

the secondary current and both voltages

by using this formula

if we knew the current on the primary

side and the voltage of the primary and

secondary we could find the secondary

current by using this formula or we

could also find the answer by using this

formula if we knew the number of turns

and then we checked the power is the

same on both sides of the transformer by

multiplying the voltage and current

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