Science & Technology in Action

12th Edition

Minimising energy loss in power transmission

Eirgrid

Metallic conductors, such as copper and aluminium, carry the electric current to our homes and places of work. However, some energy is lost along the way as heat because even the best conductors have some electrical resistance. These losses have been reduced from about 13% in 1960 to about 7.5% in 2016. Can we reduce these losses even further?
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Contains the full lesson along with a supporting toolkit, including teachers’ notes.

Lesson excerpt

Saving energy
Today we are becoming increasing aware of the need to make more efficient use of non-renewable energy resources. Traditional fossil fuel power stations are less than 40% effi cient. In other words, more than 60% of the energy in the fuel is lost as heat to the environment. By combining district heating with power generation efficiencies of 60% to 80% can be achieved.

Before we can use it electricity must get to the end users. This is done through the transmission and distribution systems. Metallic conductors, such as copper and aluminium, carry the electric current to our homes and places of work. However, some energy is lost along the way as heat because even the best conductors have some electrical resistance.

These losses have been reduced from about 13% in 1960 to about 7.5% in 2016. Can we reduce these losses even further?

Some background
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 current could be generated and scientists in Europe and America began experimenting with their own versions of the battery.

Before long they had discovered two effects of electric current:

• a heating effect and
• a chemical effect.

That year (1800) Nicholson and Carlisle decomposed water into hydrogen and oxygen ― a process known as electrolysis. Around 1808 Humphry Davy discovered several new elements using electrolysis: potassium, sodium, barium, calcium and magnesium. It is somewhat surprising that the magnetic effect of electric current was not discovered until 1820.

Although the heating effect of electric current is more obvious it was not 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 we take for granted today.

Joule’s Law
James Joule (1818–1889) spent much of his life studying these two concepts. In 1840 he replaced steam engines in his brewery with recently developed electric motors. He began to study the heat loss from conductors. Even the best conductors (silver and copper) show some resistance to electric current and may become quite hot if they carry a large electric current.

In 1841 Joule discovered that the rate of heat loss from a conductor was proportional to its resistance multiplied by the square of the electric current. Today we express this relationship mathematically as follows: P = R x Iwhere 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.

Quiz questions

  1. Transmission lines bring electricity directly to peoples’ homes. false
  2. Transformers are used to change AC to DC. false
  3. The electric battery was invented by Volta in 1800. true
  4. The unit of energy is named after James Joule. true
  5. Resistive heating is proportional to the electric current. false
  6. Electric power can be calculated by multiplying the voltage by the current. true
  7. Gold is the best electrical conductor. false
  8. Thinner wires have greater resistance. true
  9. Even the best conductors show some resistance. true
  10. Direct current is not used for transmission of electricity. false
  11. The magnetic effect of electric current was discovered in 1810. false
  12. Aluminium conductors are widely used in transmission lines. true

Glossary of terms

distribution
transfer of electrical energy from a substation to consumers
transmission
transfer of electrical energy from a generator to a substation
watt
(W) the SI unit of power. Power is the rate at which energy is transformed.
battery
a chemical cell (or more strictly, a collection of cells) that can produce a steady electric current
capacitor
a device for storing electric charge; do not confuse this with a battery, which stores energy as chemical energy, which is converted to electrical energy as the battery is utilised.
electric current
a flow of electric charge. This can be a flow of electrons (in metals) or ions (in the case of gases and ionic solutions).
kV
a kilovolt; one thousand volts
conductor
a material that conducts electricity; generally applied to good conductors such as metals
resistance
a material's opposition to the flow of electric current; measured in ohms (Ω)
alloy
a mixture of metals
magnetic field
a region of space around a magnet in which it can exerts a force on magnetic material
ionised
Converted into ions.
MW
megawatt; a measure of power; a million watts
non-renewable
once used it is not replaced takes a long time to replace
energy
the capacity to do work
electrolysis
the decomposition of a compound by passing an electric current through it; this is an example of the conversion of electrical energy to chemical energy
power
the rate at which energy is transformed
volt
the unit of electrical potential; it is a measure of the amount of energy per unit charge. 1 V = 1 J/C
ampere
The unit of measure that indicates how much electricity flows through a conductor
electric potential
voltage; a measure of the energy carried by a unit of electric charge (1 V = 1 J/C)
arcing
conduction through the air between conductors due to ionisation by high voltage
area of cross section
the area of a cut section
conductivity
the ability to conduct electricity
corona discharge
a glow in the air near high voltage sources due to ionisation of the air
direct current transmission
use of direct current rather than alternating current for power transmission
electrical resistance
the resistance of a body is a measure of how difficulty it is to pass electric current through it
heat
energy moving between two bodies, typically form the warmer to the cooler one
magnetic effect of electric current
an electric current in a conductor set up a magnetic field around the conductor
specific heat capacity
the amount of energy required to raise the temperature of one kilogram of the material by one degree Celsius
superconductor
a conductor with zero electrical resistance