Download Minimising energy loss in power transmission Minimising energy

Statement
2016-2025
Minimising ener
in power transm
Minimising energy loss
Minimising energy loss in power transmission
in power transmission
Saving energy
Saving energy
Today we are becoming
aware
of the
need
to need
make
moremore
effieffi
cient
Todayincreasing
we are becoming
increasing
aware
of the
to make
cient
use energy
of non-renewable
energyTraditional
resources. Traditional
fossilpower
fuel power
use of non-renewable
resources.
fossil fuel
stations are less than 40% efficient. In other words, more than 60% of the
stations are less thanenergy
40%ineffi
cient. In other words, more than 60% of the
the fuel is lost as heat to the environment. By combining district
energy in the fuel is lost
aswith
heat
to generation
the environment.
By
combining
heating
power
efficiencies of
60%
to 80% can district
be achieved.
heating with power generation
60%
80%
achieved.
Before we caneffi
useciencies
it electricityof
must
get to
to the
endcan
users.be
This
is done
through the transmission and distribution systems. Metallic conductors,
Before we can use itsuch
electricity
get to the
end
users. current
This istodone
as coppermust
and aluminium,
carry
the electric
our homes
and places
of work.
However, some
energy isMetallic
lost along conductors,
the way as heat
through the transmission
and
distribution
systems.
even the
best the
conductors
havecurrent
some electrical
resistance.
such as copper and because
aluminium,
carry
electric
to
our
homes
These losses have been reduced from about 13% in 1960 to about 7.5%
and places of work. However,
energy
is lost
along
the way as heat
in 2016. Can some
we reduce
these losses
even
further?
because even the best conductors have some electrical resistance.
Some
background
These losses have been
reduced
from about 13% in 1960 to about 7.5%
in 2016. Can we reduce
these
losses
even
further?
In a letter
dated
20th March
1800
Alessandro Volta (1745–1827) described
the construction of a battery. He demonstrated his invention in Paris and
news of the device spread quickly. For the first time a continuous electric
Some background
current could be generated and scientists in Europe and America began
experimenting with their own versions of the battery.
In a letter dated 20th Before
March
1800 Alessandro Volta (1745–1827) described
long they had discovered two effects of electric current:
the construction of a battery. He demonstrated his invention in Paris and
• a heating effect and
news of the device spread quickly. For the first time a continuous electric
• a chemical effect.
current could be generated
and scientists in Europe and America began
experimenting with their
own(1800)
versions
of the
battery.
That year
Nicholson
and Carlisle
decomposed water into hydrogen
Before
•
•
Power
station
Power
station
Distribution line
Apar
best
copp
gold
240 V
silve
its re
were
Step-up transformer
Step-down transformer
woul
the r
resp
Step-down transformer
Step-up transformer
Electric power
area of cross section of the alumin
The power transferred over electric cables depends on the voltage
the others because of its low density
and the current. This can be written as follows: P = V × I , where P is
would give it the lowest resistance
the power (that is the energy per unit time), V is the electric potential
(and best conductivity) per unit
maso
area
(or voltage) and I is the electric current.
Aluminium is also the best choice in
The power transferred over electric cables depends on the voltage
ot
of cost. However, in practice the
an allo
In
Ireland,
in Europe
generally,
thewritten
domestic as
electricity
supply
and
the and
current.
This
can be
follows:
P = V × I , where
is
used inPtransmission
lines towould
operates at about 240 volts. On this system a jug kettle with a current
it greater strength, although
the
thea energy
perVunit
is the electricgive
potential
(andit hb
of
10 power
amperes(that
wouldis
have
power of: 240
× 10time),
A = 2400Vwatts.
about 10% more resistance.
In
words, itand
wouldI transfer
2400 joules
per second to the water in
(orother
voltage)
is the electric
current.
Alumi
the kettle. It would raise the temperature of a litre of water by more than
of cos
Other losses
half
a
degree
every
second,
since
the
specifi
c
heat
capacity
of
water
In Ireland, and in Europe generally, the domestic electricity supply
used i
is about 4200 J kg−1 K−1 (2400 /4200= 0.57)
can be lost in transmission
operates at about 240 volts. On this system a jug kettle withEnergy
a current
heating of the conducting cables.
giveAlit
of 10 amperes
wouldvoltage
have a power
of: 240 V × 10 A = 2400alternating
watts. magnetic fields which in
Why
we use high
in transmission
about
inductive
effect
can be reduced by s
In
other
words,
it
would
transfer
2400
joules
per
second
to
the
water
in
The main power transmission lines in Ireland operate at 110 kV to 400 kV
reasonably
possible.
the
kettle. current.
It would
theassume
temperature
of aoperate
litre ofatwater by more than
of
alternating
For raise
simplicity
that these lines
Anyof
pair
of conductors that are near
direct
current.
In that
case, second,
if a 220 kV since
line canthe
safely
carry a c
current
1000
half a
degree
every
specifi
heatofcapacity
water
storing energy in an electric field. In
amperes then the maximum
that can be transmitted on it is 220 MW.
−1 power
−1
is about 4200 J kg K (2400 /4200= 0.57)
Energ
effects are unavoidable but they
red
P = (220,000 V ) × (1000 A ) = 220,000,000 W = 220 MW
user. These effects can be largely
o
heatin
transmission. However, stepping D
To transmit the same power at 110,000 volts would require a current of
altern
DC
transmission
is
economical
only
2000 amperes; this would exceed the limit of that conductor. Power can
induc
the sub-sea East–West Interconnec
be transmitted much more efficiently by using high voltage.
110 kV – 400110
kV kV –
transmission line
400 kV
transmission line
e.g. 10 k V
Electric power
Minimising energy loss
in power transmission
and oxygen ― a process known as electrolysis. Around 1808 Humphry
long they hadDavy
discovered
effects
of electric
current: potassium,
discovered two
several
new elements
using electrolysis:
sodium, barium, calcium and magnesium. It is somewhat surprising that the
a heating effect
and effect of electric current was not discovered until 1820.
magnetic
Although the heating effect of electric current is more obvious it was not
a chemical effect.
studied in detail until the 1840s. Part of the reason for this was the rather
poor understanding at that time of the concepts of heat and energy —
concepts that
take for granted
today.
Nicholson
andweCarlisle
decomposed
water into hydrogen
That year (1800)
and oxygen ― a process known as electrolysis. Around 1808 Humphry
Joule’s Law
Davy discovered several new elements using electrolysis: potassium,
Jamesand
Joulemagnesium.
(1818–1889) spent
of his life studying
these two
sodium, barium, calcium
It ismuch
somewhat
surprising
that the
concepts. In 1840 he replaced steam engines in his brewery with
magnetic effect of electric
current
wasmotors.
not discovered
untilthe
1820.
recently developed
electric
He began to study
heat loss from
conductors. Even the best conductors (silver and copper) show some
Although the heatingresistance
effect oftoelectric
current
more
obvious
not a large
electric current
and is
may
become
quite hotitifwas
they carry
current. Part of the reason for this was the rather
studied in detail untilelectric
the 1840s.
poor understanding at
thatJoule
timediscovered
of the concepts
and
energy
— was
In 1841
that the rateof
of heat
heat loss
from
a conductor
proportional
to its resistance
concepts that we take
for granted
today. multiplied by the square of the electric current.
2
Joule’s Law
Today we express this relationship mathematically as follows: P = R × I
where P is the power (that is the energy produced per unit time), R is the
resistance and I is the electric current. This was an important discovery.
An example
James Joule (1818–1889)
spent much of his life studying these two
concepts. In 1840 heThe
replaced
steam engines
his brewery
electrical resistance
of a piece in
of copper
wire 100 with
metres long and
0.7
millimetre
in diameter
is approximately
onethe
ohmheat
(R = 1loss
Ω ). Iffrom
this wire
recently developed electric motors.
He began
to study
carries a current of 2 amperes then the heat loss per second is given by: (P)
conductors. Even the
best
conductors
copper)
some (i.e. 1
2
) J/s
= 4 J/s. If the (silver
length ofand
the wire
were tenshow
times greater
= (1)(2
resistance to electric
current
may would
become
if they
a large
km),
then theand
resistance
be tenquite
ohms hot
and the
rate ofcarry
heat loss
would
be (10)(22) or 40 J/s.
electric current.
However, if the electric current were now made ten times greater the rate
2
In 1841 Joule discovered
the rate
of heattimes
lossgreater:
from (10)(20
a conductor
wasSo,
) = 4000 J/s.
of heat that
loss would
be a hundred
energy lossmultiplied
can be minimised
by keeping
theof
electric
current low.
proportional to its resistance
by the
square
the electric
current.
Today we express this relationship mathematically as follows: P = R × I 2
where P is the power (that is the energy produced per unit time), R is the
resistance and I is the electric current. This was an important discovery.
An example
The electrical resistance of a piece of copper wire 100 metres long and
0.7 millimetre in diameter is approximately one ohm (R = 1 Ω ). If this wire
carries a current of 2 amperes then the heat loss per second is given by: (P)
= (1)(22) J/s = 4 J/s. If the length of the wire were ten times greater (i.e. 1
km), then the resistance would be ten ohms and the rate of heat loss would
be (10)(22) or 40 J/s.
However, if the electric current were now made ten times greater the rate
of heat loss would be a hundred times greater: (10)(202) = 4000 J/s. So,
energy loss can be minimised by keeping the electric current low.
ChD
Oth
Why we use high voltage in transmission
The main power transmission lines in Ireland operate at 110 kV to 400 kV
reaso
As
saw earlier, current.
the energy For
loss is
proportionalassume
to the square
the
of we
alternating
simplicity
thatof these
lines operate at
Skin effect and corona
current,
by halving
current
the if
energy
losskV
would
reduced
Any p
direct so
current.
Inthe
that
case,
a 220
linebecan
safely carry a current of 1000
to 25% of it previous value. Distribution lines operate at lower voltage
When large conductors carrystorin
large a
amperes
then
theinmaximum
be transmitted
on
it is 220 MW.
and
so the total
current
them is muchpower
greater that
than incan
transmission
lines.
of the current is confined to the oute
Also, distribution lines are shorter but there are more of them.
or ‘skin’ of the conductor. Theeffect
skin d
P = distribution
(220,000losses
V ) ×are(1000
A3) to=6220,000,000
W = 220depends
MW on the material anduser.
For this reason
typically
times greater than
on the
transmission losses.
At 50 Hz the skin depth is around
8
trans
To transmit the same power at 110,000 volts would require acopper
current
of
and around
10 mm for alumi
DC
tra
net effect
is an increase in the a
2000 amperes; this would exceed the limit of that conductor.The
Power
can
Quantitymuch more effi
Unitciently by using high voltage. resistance of the conductor. The
the effe
su
be
transmitted
Quantity
Unit
Meaning
Symbol
Symbol
reduced by the use of multicore cab
cable is also more flexible and durab
As
we saw earlier, the energy losstheisrate
proportional
to the square
of the
of flow of electric
Electric
I = Q/t
ampere A = C/s
At very high potentials (e.g. 500 kV)
in coulombs
second be reduced
current so by halving the current charge
current,
the energy
lossperwould
near the cable may become ionised
toElectric
25% of it previous value. Distribution
lines
operate
at lower
voltage
the electric
charge
transferred
When
capable
of conducting electric
curre
= I t current
coulomb in Cthem
= A s isbymuch
one ampere
in one
second
and
so theQtotal
greater
than
in transmission
lines. Apart from
cables or to pylons.
los
charge
of athe
the resulting ‘arcing’ or ‘corona dis
Also,
distribution lines are shorterthe
but
there are more of them.
or ‘ski
energy carrier by each
Electric
creates noise and electromagnetic
For
this reason
losses
are typically
to 6
times greater
than cables anddepen
one volt is3one
joule
potential
V = E/Q distribution
volt
V=
J/C coulomb;
and may damage
insula
per coulomb
(voltage)
transmission
losses.
larger the diameter of the cable
At the
50
effect.
The
corona
effect
is
also
redu
energy is the capacity to do
coppe
joule
use of multiple smaller cables
(typic
J = N m work, so work and energy have
Energy
E
instead of one large cable. Their
Thelarg
n
the same unit (the joule);
kilowattkW h
area keeps them cooler and resist
they ar
1 kWUnit
h = 3,600,000 J or 3.6 MJ
hour
Quantity
used today in transmission lines (rig
Quantity
Unit
Meaning
Skin
Symbol
Symbol
Electric
current
I = Q/t
ampere
A = C/s
the rate of flow of electric
charge in coulombs per second
Electric
charge
Q=It
coulomb
C=As
the electric charge transferred
by one ampere in one second
Electric
potential
(voltage)
V = E/Q
volt
V = J/C
the energy carrier by each
coulomb; one volt is one joule
per coulomb
joule
Energy
E
kilowatthour
J=Nm
kW h
energy is the capacity to do
work, so work and energy have
the same unit (the joule);
1 kW h = 3,600,000 J or 3.6 MJ
reduc
cable
At ver
near t
capab
cable
the re
create
and m
larger
effect
use o
instea
area k
used
All-Island
Generation
Capacity
ng energy loss
Statement
transmission
2016-2025
Minimising energy loss in power
transmission
Choice of conductorChoice of conductor
Distribution line
Apart from superconductors, silver
the superconductors,
best conductor of electricity,
Apartisfrom
silver is the
followed by copper (95% of the best
conductivity
gold followed
(69%) by
conductorofofsilver),
electricity,
10 kIfV1 kg of copper
and aluminiume.g.
(60%).
silver were
a wire 1 kmofinsilver),
length
(95%made
of theinto
conductivity
its resistance would be 168 Ω. Ifgold
the (69%)
same were
done with (60%).
1 kg of Ifcopper
and aluminium
1 kg of
240
V be 150 Ω. silver
the resistance
would
For gold
and
aluminium
the resistances
were
made
into a wire
1 km in length
would be 440 Ω and 72 Ω respectively.
The reason
thesame
its resistance
would for
be this
168isΩ.that
If the
area of cross section of the aluminium
wire
would
much greater
than
were done
with
1 kg be
of copper
the resistance
wn transformer
all the others because of its lowwould
density;
the lowest
bethis
150would
Ω. Forgive
goldit and
aluminium
resistance (and best conductivity)
unit
theper
resistances
would be 440 Ω and 72 Ω
mass. Aluminium is also the best
choice
respectively.
The reason for this is that the
in
terms
ofcost.section
However,
an wire would be much greater than all
area
of cross
of inpractice
the aluminium
alloy
of aluminium
in transmission
the others
becauseisofused
its low
density; this
lines
giveititthe
greater
strength,
although
wouldtogive
lowest
resistance
l
it(and
hasbest
about
10% more resistance.
conductivity)
per unit mass.
Relative of size of silver, copper, gold
Aluminium is also the best choice in terms and aluminium conductors of equal
of cost. However, in practice an alloy of
aluminium
length and
weight. is
Other
losses
used in transmission
lines to
Relative of size of silver, copper, gold
t
give it greater strength, although it has
and aluminium conductors of equal
Energy can be lost in transmission in other ways,
apart from resistive
length and weight.
about 10% more resistance.
n
heating of the conducting cables. Alternating currents in power lines produce
an
alternating magnetic fields which induce currents in nearby lines. These
Other losses
er
inductive effect can be reduced by separating the conductors as much as is
reasonably
Energy canpossible.
be lost in transmission in other ways, apart from resistive
heating
conducting
Alternating
currents
in power
lines produce
Any
pairof
ofthe
conductors
thatcables.
are near
one another
can act
as a capacitor,
alternating
magnetic
fields field.
whichIninduce
currents
in nearby
These
storing
energy
in an electric
AC systems
inductive
andlines.
capacitive
inductive
effect
can be reduced
by
separating
the conductors
as
much
as is
effects
are
unavoidable
but
they
reduce
the
power
delivered
to
the
end
0 kV
reasonably
user.
These possible.
effects can be largely overcome by using direct current
at
transmission.
However,
stepping
DCone
up another
or downcan
is more
costly
and so
Any pair of conductors
that
are near
act as
a capacitor,
of 1000
DC
transmission
only
uninterrupted
cables
such as
storing
energy in is
aneconomical
electric field.
In for
AC long,
systems
inductive and
capacitive
0 MW.
the
sub-sea
East–West Interconnector
Ireland
and the
U.K.
effects
are unavoidable
but they reducebetween
the power
delivered
to the
end
user. These effects can be largely overcome by using direct current
transmission.
stepping DCdischarge
up or down is more costly and so
of
Skin
effectHowever,
and corona
DC transmission is economical only for long, uninterrupted cables such as
an
When
large conductors
large alternating
currents
A) much of
the sub-sea
East–West carry
Interconnector
between
Ireland(e.g.
and 2000
the U.K.
the current is confined to the outer layer or ‘skin’ of the conductor. The skin
depth depends on the material and on the frequency. At 50 Hz the skin depth
Skin effect and corona discharge
is around 8 mm for copper and around 10 mm for aluminium. The net effect is
an
increase
the apparent
resistance
of the currents (e.g. 2000 A) much
When
large in
conductors
carry
large alternating
ines.
conductor.
Theiseffect
is reduced
by the
use
of the current
confined
to the outer
layer
of
cable;
such cable
is also
more
or multicore
‘skin’ of the
conductor.
The skin
depth
an
flexible
and
depends
ondurable.
the material and on the frequency.
At 50 Hz the skin depth is around 8 mm for
At very high potentials (e.g. 500 kV) the air
copper and around 10 mm for aluminium.
near the cable may become ionised and
The net effect is an increase in the apparent
capable of conducting electric current to
resistance of the conductor. The effect is
other cables or to pylons. Apart from a loss
reduced by the use of multicore cable; such
of power the resulting ‘arcing’ or ‘corona
cable is also more flexible and durable.
Steel
reinforcedand
andcomposite
composite
Steel reinforced
discharge’ creates noise and electromagnetic
core aluminium
core
aluminiumconductors
conductors
interference
may damage
cables
andair
At very high and
potentials
(e.g. 500
kV) the
econd
insulation.
The may
largerbecome
the diameter
of and
the
near the cable
ionised
erred
cable
theofless
the effect.
The corona
is
capable
conducting
electric
currenteffect
to other
cond
also
reduced
by the Apart
use offrom
multiple
smaller
cables
or to pylons.
a loss
of power
cables
(typically
four) or
instead
of one
large
the resulting
‘arcing’
‘corona
discharge’
h
cable.
larger
surface area keeps
them
createsTheir
noise
and electromagnetic
interference
joule
cooler
anddamage
they arecables
commonly
used today
in
and may
and insulation.
The
transmission
lines (right).
larger the diameter
of the cable the less the
effect. The corona effect is also reduced by the
do
use of multiple smaller cables (typically four)
y have
instead of one large cable. Their larger surface
area keeps them cooler and they are commonly
3.6 MJ
used today in transmission lines (right).
EirGrid is responsible for a safe, secure and reliable supply
of electricity: Now and in the future.
We develop, manage and operate the electricity transmission
grid. This brings power from where it is generated to where
it is needed – throughout Ireland. We use our grid to supply
power to industry and businesses that use large amounts
of electricity. Our grid also powers the distribution network.
This supplies the electricity you use everyday in your homes,
businesses, schools, hospitals, and farms.
Minimising energy loss
in power transmission
Image
Image source:
source: Wikipedia
Wikipedia
We develop new electricity infrastructure only when required.
EirGrid is a state-owned company, but we answer to
government and to regulators. We work for the benefit and
safety of every citizen in Ireland; we abide by strict laws
and safety standards.
You can find out more about the work of EirGrid at
www.eirgrid.com
Find this and other lessons on www.sta.ie
Minimising
Minimisingenerg
ener
in
inpower
powertransm
transm
Minimising energy loss in power transmission
Exa
Ex
Syllabus
SyllabusReferences
References
Student
StudentActivities
Activities
The
Themain
mainsyllabus
syllabusreferences
referencesforforthe
thelesson
lessonare:
are:
1.1. The
Theresistivity
resistivity(ρ),
(ρ),oror
1m
1m
1m
1m
specifi
specifi
c cresistance,
resistance,ofofa a
material
materialisisthe
theresistance
resistance
ofofa auniform
uniformsample
sampleofof
the
thematerial
materialofofunit
unitlength
length
1m
1 2m2
1m
1 2m2
and
andunit
unitcross
crosssection.
section.
(In(Inpractice
practicethis
thiswould
wouldbebe
virtually
virtuallyimpossible
impossibletotomeasure
measuredirectly.)
directly.)
−8 −8
ΩΩm.m.
The
Theresistivity
resistivityofofcopper
copperisis1.68
1.68× ×1010
Show
Showthat
thatif ifa acubic
cubicmetre
metreofofcopper
copperwere
wereformed
formedinto
intoa auniform
uniform
2 2
it itwould
wouldbebe1000
1000km
kmininlength
length
wire
wirewith
witha across
crosssection
sectionofof1 1mm
mm
4 4
ΩΩoror16.8
16.8kΩ.
kΩ.
and
anditsitsresistance
resistancewould
wouldbebe1.68
1.68× ×1010
Leaving
LeavingCertifi
Certifi
cate
catePhysics
Physics(pp.
(pp.36–38)
36–38)
• • Resistance:
Resistance:
Defi
Defi
nition
nitionofofresistance,
resistance,unit.
unit.Ohm’s
Ohm’slaw.
law.
Resistance
Resistancevaries
varieswith
withlength,
length,cross-sectional
cross-sectionalarea,
area,and
and
temperature.
temperature.Resistivity.
Resistivity.Resistors
Resistorsininseries
seriesand
andparallel.
parallel.
Thermistor.
Thermistor.
• • Potential:
Potential:Potential
Potentialdivider.
divider.
• • Heating:
Heating:WW= =I 2IR2 Rt. t.
Chemical:
Chemical:ananelectric
electriccurrent
currentcan
cancause
causea achemical
chemicalreaction.
reaction.
Magnetic
Magneticeffect
effectofofananelectric
electriccurrent.
current.
• • Magnetic
Magneticfields:
fields:Magnetic
Magneticfield
fielddue
duetotomagnets,
magnets,current
currentinina along,
long,
a aloop
looporora asolenoid.
solenoid.
• • Alternating
Alternatingcurrent:
current:Peak
Peakand
andr m
rm
s svalues.
values.
Science
Scienceand
andTechnology
Technologyinin
Action
Actionisisalso
alsowidely
widelyused
usedbyby
Transition
TransitionYear
Yearclasses.
classes.
Learning
LearningOutcomes
Outcomes
Minimising energy loss
in power transmission
On
Oncompletion
completionofofthis
thislesson,
lesson,students
studentsshould
shouldbebeable
ableto:to:
•
•
•
•
•
•
•
•
•
•
•
•
•
•
2.2. The
Thetable
tableshows
showsthe
the
3 3
–3 –3
Silver
Silver
10.49
10.49
××
1010
kgkg
mm
densities
densitiesofofsilver,
silver,copper
copper
and
andaluminium.
aluminium.Show
Showthat
that
3 3
–3 –3
Copper
Copper
8.96
8.96
××
1010kgkg
mm
the
thevolume
volumeofofone
onekilogram
kilogram
3 3
–3 –3
Aluminium 2.65
2.65
××
1010
kgkg
mm
ofofthese
thesemetals
metalswould
wouldbebe95,
95, Aluminium
3 3
respectively.
respectively.
112
112and
and377
377cm
cm
outline
outlinethe
thegeneral
generalstructure
structureand
andfunction
functionofofthe
thenational
nationalgrid
grid
calculate
calculatepower
powergiven
giventhe
thevoltage
voltageand
andcurrent
current
explain
explainwhat
whatisismeant
meantbybyresistive
resistiveheating
heating
calculate
calculateenergy
energyloss
lossgiven
giventhe
theresistance
resistanceand
andcurrent
current
describe
describethe
thefunction
functionofofa atransformer
transformer
explain
explainwhy
whyhigh
highvoltages
voltagesare
areused
usedinintransmission
transmissionlines
lines
give
givereasons
reasonswhy
whyaluminium
aluminiumisisthe
thebest
bestchoice
choiceofofconductor
conductorforfor
transmission
transmissionlines.
lines.
General
GeneralLearning
LearningPoints
Points
These
Theseare
areadditional
additionalrelevant
relevantpoints
pointswhich
whichare
are
used
usedtotoextend
extendknowledge
knowledgeand
andfacilitate
facilitatediscussion.
discussion.
• • Under
Underordinary
ordinaryconditions
conditionsallallmetals
metalshave
havesome
someelectrical
electrical
resistance.
resistance.
AsAsa aresult
resultthey
theybecome
becomehot
hotwhen
whencarrying
carryinglarge
large
currents.
currents.The
Theheating
heatingeffect
effectisisproportional
proportionaltotothe
thesquare
squareofofthe
the
electric
electriccurrent.
current.
• • Transmitted
Transmittedpower
powerisiscalculated
calculatedbybymultiplying
multiplyingthe
thevoltage
voltagebybythe
the
current.
current.The
Thesame
samepower
powercan
canbebetransmitted
transmittedbybyincreasing
increasingthe
the
voltage
voltageand
andlowering
loweringthe
thecurrent
currentbybythe
thesame
samefactor.
factor.Less
Lessenergy
energy
isislost
lostbybyusing
usinghigher
highervoltage.
voltage.
• • The
Thetransmission
transmissionlines
linesininthe
theNational
NationalGrid
Gridoperate
operateatat400,000
400,000V.V.
• • Transformers
Transformersare
areused
usedtotostep
stepthe
thevoltage
voltageupuporordown
down
asasrequired.
required.
• • Energy
Energyisislost
lostthrough
throughresistive
resistiveheating
heatingmainly
mainlyininthe
thedistribution
distribution
lines
lineswhich
whichoperate
operateatatlower
lowervoltages
voltagesand
andcorresponding
correspondinghigher
higher
overall
overallcurrent.
current.
• • Although
Althoughaluminium
aluminiumisisnot
notthe
thebest
bestconductor
conductorofofelectricity
electricitywhen
when
compared
comparedwith
withother
otherconductors
conductorsofofthe
thesame
samelength
lengthand
andweight
weightit it
isisabout
abouttwice
twiceasasgood
goodasassilver
silverand
andcopper.
copper.
3.3. The
Thetable
tableshows
showsthe
theresistivities
resistivitiesofofsilver,
silver,copper
copperand
andaluminium.
aluminium.
If Ifone
onekilogram
kilogramofofeach
eachofofthe
themetals
metalsabove
above(Q.
(Q.3)3)were
weremade
made
into
intoa aone
onekilometre
kilometrewire
wireshow
showthat:
that:
a)a)their
theircross
crosssections
sectionswould
would
−8 −8
2 2
Silver
Silver
10.49
10.49
××
1010
ΩΩ
mm
bebe9.5,
9.5,11.2
11.2and
and37.7
37.7mm
mm
−8 −8
respectively
respectively
Copper
Copper
1.68
1.68
××
1010
ΩΩ
mm
b)b)their
theirresistances
resistanceswould
would
−8 −8
Aluminium
Aluminium 2.65
2.65
××
1010
ΩΩ
mm
bebe1.67,
1.67,1.50,
1.50,0.703
0.703ΩΩ
respectively.
respectively.(R(R= =ρ ρl /l A/ A
) )
How
Howdoes
doesthis
thisillustrate
illustratethe
theadvantage
advantageofofusing
usingaluminium
aluminiumasasa a
conductor
conductorforforelectricity
electricitytransmission?
transmission?
Leav
Le
R
“
The
Th
cons
con
lines
line
Irela
Ire
lowe
low
The
Th
unde
und
whic
wh
dista
dis
Pow
Po
varie
var
elect
ele
land
lan
AtAtth
into
into
2.1
2.1m
(
(
(
(
True/False
True/FalseQuestions
Questions
(
a)a)Transmission
Transmissionlines
linesbring
bringelectricity
electricitydirectly
directlytotopeoples’
peoples’
homes.
homes.
T TF F
(
b)b)Transformers
Transformersare
areused
usedtotochange
change
AC
ACtotoDC.
DC.
T TF F
c)c) The
Theelectric
electricbattery
batterywas
wasinvented
inventedbybyVolta
Voltainin1800.
1800.
T TF F
d)d)The
Theunit
unitofofenergy
energyisisnamed
namedafter
afterJames
JamesJoule.
Joule.
T TF F
(
e)e)Resistive
Resistiveheating
heatingisisproportional
proportionaltotothe
theelectric
electriccurrent.
current.
T TF F
(
9. 9. What
What
is is
electromagnetic
electromagnetic
induction?
inductio
f) f) Electric
Electricpower
powercan
canbebecalculated
calculatedbybymultiplying
multiplyingthe
thevoltage
voltage
Describe
Describe
anan
to to
demonst
demon
bybythe
thecurrent.
current.
Texperiment
Texperiment
FF
Leav
Le
g)g)Gold
Goldisisthe
thebest
bestelectrical
electricalconductor.
conductor.
h)h)Thinner
Thinnerwires
wireshave
havegreater
greaterresistance.
resistance.
T TF F
Nam
Nao
The
The
transformer
transformer
is is
a device
a device
based
based
Tdevices
T F Fthat
Name
Name
two
two
devices
that
useuse
transfor
transf
The
Th
supp
sup
T TF F
conn
con
j) j) Direct
Directcurrent
currentisisnot
notused
usedforfortransmission
transmissionofofelectricity.
electricity.
T
T
F
F
Name
Name
thethe
parts
parts
ofof
thethe
transformer
transformer
la
400
400
k)k) The
Themagnetic
magneticeffect
effectofofelectric
electriccurrent
currentwas
wasdiscovered
discovered
Wha
Wh
inin1810.
1810.
Telectricity
T F F supply
voltm
volV
The
The
mains
mains
electricity
supply
(230
(230
i) i) Even
Eventhe
thebest
bestconductors
conductorsshow
showsome
someresistance.
resistance.
turns.
turns.C C
hashas
100
100
turns.
turns.What
What
is is
thet
l) l) Aluminium
Aluminiumconductors
conductorsare
arewidely
widelyused
usedinintransmission
transmission
lines.
lines.
T TF F
Check
Checkyour
youranswers
answerstotothese
thesequestions
questionsononwww.sta.ie.
www.sta.ie.
How
How
is is
thethe
part
part
labelled
labelled
BB
designed
design
The
The
efficiency
efficiency
ofof
a transformer
a transformer
is is
9
ViVi NpNp
VoVo NsNs
( ( == ) )
ng
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energyloss
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ransmission
orm
m
ngth
th
m
–3 –3
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m.
um.
e
m
m
Minimising energy loss in power transmission
Examination
ExaminationQuestions
Questions
Did
DidYou
YouKnow?
Know?
Leaving
LeavingCertifi
Certifi
cate
catePhysics
Physics(OL)
(OL)2013,
2013,Q.Q.1111
• • The
The
demand
demand
forfor
electricity
electricity
varies
varies
with
with
the
the
time
time
ofof
day,
day,
the
the
seasons,
seasons,
the
the
weather
weather
and
and
even
even
with
with
patterns
patterns
ofof
TVTV
viewing.
viewing.The
The
graph
graph
shows
shows
the
the
varying
varying
All-Island
All-Island
demand
demand
(and
(and
anticipated
anticipated
st st
Aug.
Aug.
2016.
2016.
demand)
demand)
onon
Sunday
Sunday
2121
• • The
The
supply
supply
ofof
electricity
electricity
must
must
match
match
the
the
demand.
demand.
Renewable
Renewable
energy
energy
sources
sources
make
make
aa
signifi
signifi
cant
cant
contribution
contribution
inin
windy
windy
weather
weather
but
but
other
other
forms
forms
ofof
energy
energy
are
are
also
also
necessary
necessary
toto
meet
meet
the
the
demand.
demand.
Read
Read
this
this
passage
passage
and
and
answer
answer
the
the
questions
questions
below.
below.
“The
“The
National
National
Grid
Grid
- Ireland’s
- Ireland’s
Transmission
Transmission
System
System
The
The
national
national
grid
grid
system
system
supplies
supplies
electricity
electricity
toto
customers.
customers.
The
The
grid
grid
consists
consists
ofof
aa
network
network
ofof
high
high
voltage
voltage
transmission
transmission
stations,
stations,
power
power
lines
lines
and
and
cables
cables
delivering
delivering
power
power
toto
over
over
100
100
sub-stations
sub-stations
allall
over
over
Ireland.
Ireland.
From
From
these
these
sub-stations
sub-stations
power
power
can
can
bebe
taken
taken
onwards
onwards
onon
lower
lower
voltage
voltage
lines
lines
toto
individual
individual
customers’
customers’
premises.
premises.
The
The
network
network
includes
includes
about
about
6,000
6,000
km
km
ofof
overhead
overhead
lines
lines
and
and
underground
underground
cables.
cables.
High
High
voltages
voltages
are
are
used
used
toto
avoid
avoid
power
power
losses
losses
which
which
would
would
otherwise
otherwise
occur
occur
when
when
transferring
transferring
power
power
over
over
long
long
distances.
distances.
AtAt
the
the
sub-stations
sub-stations
power
power
is is
transferred
transferred
from
from
the
the
grid,
grid,
transformed
transformed
into
into
medium
medium
and
and
low
low
voltage
voltage
electricity
electricity
and
and
is is
delivered
delivered
toto
Ireland’s
Ireland’s
2.1
2.1
million
million
domestic,
domestic,
commercial
commercial
and
and
industrial
industrial
customers.”
customers.”
(Adapted
(Adapted
from
from
EIRGRID
EIRGRID
ATAT
A GLANCE,
A GLANCE,
Eirgrid
Eirgrid
information
information
publication.)
publication.)
m
a
sa
(b)(b)Why
Why
are
are
high
high
voltages
voltages
used
used
toto
transmit
transmit
power
power
over
over
the
the
national
national
grid?
grid?
TF F
TF F
4000
4000
2000
2000
anticipated
anticipated
demand
demand
0 0
The
The
data
data
below
below
show
show
the
the
mix
mix
ofof
st st
August
August
2016.
2016.
sources
sources
atat
21:38
21:38
onon
2121
Note
Note
the
the
net
net
import
import
shows
shows
aa
negative
negative
number;
number;
this
this
means
means
that
that
some
some
electricity
electricity
was
was
exported
exported
viavia
the
the
Interconnector.
Interconnector.
Minimising energy loss
in power transmission
Power
Power
is is
generated
generated
byby
power
power
plants
plants
throughout
throughout
the
the
country,
country,
using
using
aa
variety
variety
ofof
fuel
fuel
oror
energy
energy
sources,
sources,
including
including
gas,
gas,
oil,oil,
coal,
coal,
peat,
peat,
hydrohydroelectricity,
electricity,
wind
wind
turbines
turbines
and
and
other
other
sources
sources
such
such
asas
biomass
biomass
and
and
landfi
landfi
ll gas.
ll gas.
AllAll
ofof
the
the
major
major
power
power
plants
plants
feed
feed
into
into
the
the
national
national
grid.
grid.
(a)(a)
What
What
are
are
the
the
key
key
components
components
ofof
the
the
national
national
grid?
grid?
TF F
MWMW
(d)(d)Name
Name
two
two
renewable
renewable
and
and
two
two
non-renewable
non-renewable
energy
energy
sources
sources
used
used
toto
generate
generate
electricity.
electricity.
(e)(e)The
The
national
national
grid
grid
uses
uses
alternating
alternating
current
current
(a.c.)
(a.c.)
rather
rather
than
than
direct
direct
current
current
(d.c.).
(d.c.).
What
What
is is
the
the
difference
difference
between
between
them?
them?
(f)(f)Name
Name
the
the
device
device
used
used
toto
convert
convert
high
high
voltages
voltages
toto
lower
lower
voltages.
voltages.
TF F
(g)(g)Give
Give
the
the
principle
principle
ofof
operation
operation
ofof
the
the
device
device
named
named
inin
part
part
(f).(f).
TF F
(h)(h)Name
Name
the
the
unit
unit
ofof
electrical
electrical
energy
energy
that
that
is is
used
used
inin
the
the
delivery
delivery
(9)(9)
periment
demonstrate
demonstrate
electromagnetic
electromagnetic
induction.
induction.
Texperiment
F F to to
Leaving
Leaving
Certifi
Certifi
cate
cate
Physics
Physics(OL)
(OL)2002,
2002,Q.Q.9 9
(6)(6)
supply
supply
(230
(230
V)V)
is is
connected
connected
toto
A,A,
which
which
has
has
Trts
F
F
of of
thethe
transformer
transformer
labelled
labelled
A,
B
and
B
and
C100
in
C in
theturns.
the
diagram.
diagram.
400
400
turns.
turns.
CA,
C
has
has
100
turns.
What
What
is is
the
the
reading
reading
onon
the
the (9)(9)
Ttricity
F F supply
voltmeter?
voltmeter?
ectricity
supply
(230
(230
V)V)
is connected
is connected
to to
A,A,
which
which
hashas
400
400
TF F
V V
100
0 turns.
turns.What
What
is the
is the
reading
reading
onon
thethe
voltmeter?
voltmeter? (9)(9)
TF F
AA
BB
InIn
December
December
1922
1922
bebe
began
began
working
workingforfor
Siemens
Siemens
in in
Germany.
Germany.
AtAt
the
the
time
time
the
the
company
company
was
was
developing
developing
hydroelectric
hydroelectric
power
power
plants.
plants.
McMc
Loughlin
Loughlin
was
was
familiar
familiar
with
with
the
the
many
many
previous
previous
proposals
proposals
toto
use
use
the
the
Shannon
Shannon
asas
aa
source
source
ofof
hydro
hydro
power.
power.
With
With
the
the
backing
backing
ofof
Siemens
Siemens
hehe
went
went
toto
Ireland
Ireland
in in
1923
1923
and
and
met
met
with
with
members
members
ofof
the
the
new
new
Free
Free
State
State
Government.
Government.
His
His
proposals
proposals
were
were
initially
initially
turned
turned
down
down
but
but
in in
January
January
1924
1924
hehe
returned,
returned,
accompanied
accompanied
byby
a senior
a senior
director
director
ofof
Siemens.
Siemens.
This
This
time
time
the
the
proposal
proposal
st
May
1925
1925
was
was
accepted.
accepted.
Detailed
Detailed
plans
plans
were
were
drawn
drawn
upup
and
and
onon
1st1May
the
the
Shannon
Shannon
Electricity
Electricity
BillBill
was
was
introduced
introduced
in in
the
the
Dáil.
Dáil.
Despite
Despite
further
further
opposition
opposition
from
from
vested
vested
interests
interests
(e.g.
(e.g.
local
local
electricity
electricity
suppliers
suppliers
in in
Dublin
Dublin
and
and
elsewhere)
elsewhere)
the
the
contract
contract
was
was
signed
signed
and
and
work
work
began
began
later
later
that
that
year.
year.
The
The
Electricity
Electricity
Supply
Supply
Board
Board
(ESB)
(ESB)
was
was
setset
upup
in in
1927,
1927,
with
with
McMc
Loughlin
Loughlin
asas
executive
executive
director.
director.
HeHe
was
was
just
just
3131
years
years
ofof
age.
age.
Wikipedia:
Wikipedia:
Thomas_McLaughlin_(engineer)
Thomas_McLaughlin_(engineer)
Wikipedia:
Wikipedia:
Shannon_hydroelectric_scheme
Shannon_hydroelectric_scheme
(12)
(12)
T
F F a device
Name
Name
the
the
parts
parts
of
the
the
transformer
transformer
labelled
labelled
A,A,
BB
and
and
CC
inin
the
the
diagram.
diagram.
mer
r is aisdevice
based
based
onon
the
the
principle
principle
ofof
of
electromagnetic
electromagnetic
induction.
induction.
Tces
F Fthatthat
vices
useuse
transformers.
transformers.
The
The
mains
mains
electricity
electricity
DrDr
Thomas
Thomas
A.A.
Mc
Mc
Laughlin
Laughlin
(1896
(1896
−−
1971)
1971)
Although
Although
Thomas
Thomas
McMc
Laughlin
Laughlin
was
was
born
born
in in
Drogheda
Droghedahehe
was
was
educated
educated
in in
Dublin,
Dublin,
obtaining
obtaining
a BSc
a BSc
and
and
MSc
MSc
atat
UCD.
UCD.
HeHe
completed
completed
a BE
a BE
and
and
PhD
PhD
while
while
working
working
asas
anan
assistant
assistant
physics
physics
lecturer
lecturer
in in
UCG.
UCG.
(c)(c)Why
Why
is is
the
the
power
power
supplied
supplied
toto
domestic
domestic
customers
customers
atat
lower
lower
voltages?
voltages?
magnetic
romagnetic
induction?
induction? ofof
electricity
electricity
toto
homes
homes
and
and
businesses.
businesses.
Biographical
BiographicalNotes
Notes
CC
art
labelled
labelled
B designed
B designed
to to
make
make
thethe
transformer
transformer
more
more
efficient?
efficient?
(6)(6)
of
y of
a transformer
a transformer
is 90%.
is 90%.What
What
does
does
this
this
mean?
mean?
(5)(5)
Revise
ReviseThe
TheTerms
Terms
Can
Can
you
you
recall
recall
the
the
meaning
meaning
ofof
the
the
following
following
terms?
terms?
Revising
Revising
terminology
terminology
is is
aa
powerful
powerful
aid
aid
toto
recall
recall
and
and
retention.
retention.
alloy,
alloy,
ampere,
ampere,
arcing,
arcing,
area
area
ofof
cross
cross
section,
section,
battery,
battery,
capacitor,
capacitor,
conductivity,
conductivity,
conductor,
conductor,
corona
corona
discharge,
discharge,
direct
direct
current
current
transmission,
transmission,
distribution,
distribution,
electric
electric
current,
current,
electric
electric
potential,
potential,
electrical
electrical
resistance,
resistance,
electrolysis,
electrolysis,
energy,
energy,
heat,
heat,
ionised,
ionised,
kV,
kV,
magnetic
magnetic
effect
effect
ofof
electric
electric
current,
current,
magnetic
magnetic
field,
field,
MW,
MW,
non-renewable,
non-renewable,
power,
power,
resistance,
resistance,
specifi
specifi
c heat
c heat
capacity,
capacity,
superconductor,
superconductor,
transmission,
transmission,
volt,
volt,
watt.
watt.
Check
Check
the
the
Glossary
Glossary
ofof
terms
terms
for
for
this
this
lesson
lesson
onon
www.sta.ie
www.sta.ie