P1

Página 1

P1.2- Transmission of Electricity

Monitoring Electricity Demand

Days in which you may use more electricity in your home

Weekends-

Everyone's home to watch TV and charge phones/iPads

Winter-

Colder and darker

Need more heating and lights

Some might use electrical fireplaces

Christmas-

Lights on the Christmas tree

Oven to cook food

Try out new electrical appliances

Night-

Lights

TV

Sporting Events

How the National Grid Monitors Energy Usage

Information from sensors throughout the country about the weather.

If it's bad weather, more people will be inside.

A network of 1500 buoys floating around in the Irish Sea giving us a long term view of the weather.

If it's bad weather, more people will be inside.

Television companies sending data estimating the number of audience expected.

Finals & live shows will be bigger, more people will be watching, requiring more electricity.

Página 2

The Demand for Electricity

Electricity Usage in Britain-

Higher in the week than weekends

Lowest points-

around midnight

Highest Points-

Around 7-9am and 6-8 pm

What makes weekends so different-

Children are home from school

No school is using electricity

Nice weather- everyone might be out

TV Pick-up-

Demand for electricity between shows

Over how long-

5 minutes

What do they do to solve this problem-

Have backup electricity sources, specialised power stations on standby

How much power comes from France during this period-

600 MW

What frequency must he keep the electricity flowing at-

50 Hz

What can unexpectedly go wrong-

The frequency drops dramatically because of a trip in France

The biggest headache for the National Grid is trying to the right balance between supply and the demand

It is not possible to store electrical energy and so it must be produced every second of every day

Página 3

The National Grid

The electricity leaves the power station.

It then goes to a step-up transformer, increasing the voltage, decreasing the current.

This reduces heat loss and makes the National Grid more efficient.

It then goes to a step-down transformer, decreasing the voltage, increasing the current.

It is now safe to use in our homes.

Electrical Transmission

Electricity is made in many different types of power station.

It is distributed through a network called the National Grid.

The electricity produced at a power station is alternating current. (a.c.) This means it is constantly changing from positive to negative, 50 time per seconds.

In the UK, power stations produce electricity at 25,000 volts.

This is passed through step-up transformers, to increase the voltage to 400,000 volts before it is distributed.

All types of power stations use step-up transformers to substantially increase the voltage before it is distributed.

The Super Grid

Electricity is first carried around the 'Super Grid' at 400,000 Volts.

Regional Substations

The electricity carried around the 'Super Grid' arrives at a substation, where step-down transformers are used to decrease the voltage, first to 132,000 volts and then to 33,000 volts.

Large factories with huge electrical consumption take the electricity at 33,000 volts.

Secondary Distribution Network

As the electricity approaches towns and cities, it passes through substations once again, and the voltage is stepped down to 11,000 volts

Local Substations

Before being passed into houses, the electricity goes through another local step-down transformer, which further decreases the voltage to 230 volts.

Página 4

P1.3- Energy Supply and The Home

Energy is measured in Joules (J).

A 100 Watt light bulb uses 100J of energy every second it is switched on.

If the light bulb is switched on for 1 hour, it uses:

60 x 60 x 100 Joules of energy = 360,000J.

This is a very large figure, so energy is usually measured in units called kilojoules (kJ).

1 kilojoule = 1000 Joules.

A low energy 20W light bulb gives out the same amount of light as a traditional 100W bulb, but only uses 20J of energy every second it is switched on.

If the bulb is switched on for one hour it uses:

60 x 60 x 20J = 72,000J.

Saving of 288,000J (360,000J - 72,000J).

Página 5

Energy, Power & Time

Power of any appliance tells you how much energy it uses per second.

Total energy used by any appliance is equal to its power multiplied by the length of time the appliance is being used for.

Energy (Joules) = Power (Watts) x Time (Seconds)

E = P x T

E

P T

Energy Transfers

Hairdryer=

Useful Energy Transfers =

Kinetic

Heat

Wasted Energy Transfers=

Sound

Heat

Light Bulb

Useful Energy Transfers=

Light

Wasted Energy Transfers=

Heat

Página 6

The Kilowatt Hour (kWh)

The energy transferred when a power of 1 kilowatt (1000W) is used for 1 hour.

Units used (kWh) = Power (kW) x Time (H)

If a single 100W light bulb was switched on for a total of 4 hours, and the cost of a unit of electricity is 8p then..

Units used = power x time

0.1 x 4

0.4 kWh

The Cost of Appliances

Cost = number of units x price per unit

Calculate the cost of the electricity used when a 2kW heater is switched on maximum for 90 minutes, if electricity costs 10p per unit.

90 minutes = 1.5hours

Energy = 2 x 1.5 = 3kWh

3 x 10 = 30p

Página 7

Electricity Bills

Total cost of electricity used by any household depends on:

How many electrical appliances are being used

How long each appliance is used for

The power rating of each individual appliance

First step:

Use the meter to find the number of units electricity used

Previous Reading- 28501

Current Reading- 29572

Units Used- 1071

Current Meter Reading = 36329 Calculation Answer

Previous Meter Reading = 35516 36329 - 35516 813kWh

Cost per Unit of Electricity= 10 p 813 x 10 8130p

Standing Charge 18p Per Day 18 x 90 1620p

3 Months = 90 days

Total Charges 8130 + 1620 9750p (£97.50)

VAT at rate of Only 5% 97.50 / 10 /2 £4.88

Total Amount Payable 4.88 + 97.50 £102.38

Página 8

Bev's Electricity Bill

One Unit of Electricity Used = 7p

Appliance Power Rating (W) Time (h) Energy (kWh)

Shower 2,000 0.5 1000= 1kWh

Hairdryer 1800 0.25 0.45

Straighteners 1900 0.25 475 = 0.475kWh

Iron 1100 0.25 275 = 0.275kWh

Total Amount of Energy Units Used = 2.2

Total Cost of Electricity Used = 15.4p