Earth/Space: Bellringer1.) What is the difference between

conserving electricity and increasing yourelectricity efficiency?

Daily Agenda

• Electricity Notes

• Electricity Threat

Electricity• 1/3 of the energy consumed globally is

used to generate electricity– 16 trillion kWh/year.–¼ is consumed in the United States

• Electricity is a secondary source of energy.– Generated from primary sources of energy.

• Coal, natural gas, nuclear fission….– Generated in large centralized power plants.

• Most power plants consist of a spinningelectrical generator.– Spinning caused by steam heated by coal,

nuclear fission, etc.– 2/3 of energy lost as heat

• Sent out into the world

• Cooling Towers– Cools the used

steam back into hotwater, so that it canbe re-used.

– About 2/3 of the heatis wasted, only about1/3 goes toelectricity.

• Something has to spin that generator– Usually a Steam Turbine that is powered

by a primary energy source.• Burning coal, oil, or natural gas• Nuclear Reactor

• Electric generators generate 3-phaseAC power.

• The three-phase power leaves thegenerator and enters a transmissionsubstation at the power plant.

• The substation uses largetransformers

– converts the voltage up toextremely high voltages forlong-distancetransmission.

– Typical voltages for longdistance transmission are155,000-765,000 volts inorder to reduce line losses.

• A typical maximumtransmissiondistance is about300 miles.– 3 wires for 3 phases.– Extra wires are

ground wires.• Extract lightening

• For power to be used in a home orbusiness, it comes off the transmissiongrid and is stepped-down to thedistribution grid.

• The place where the conversion fromtransmission to distribution occurs is ina power substation.

• Power is distributed todifferent sets of distributionlines and leave thesubstation in differentdirections.– Power lines have three

wires for the 3-phase power.– The fourth wire lower on the

poles is the ground wire.– Sometimes additional wires

are added for phone andcable.

• Regulator Bank– Located along the

line– Regulates voltage

• Prevents overvoltageor undervoltageconditions

• Taps– A house needs only

one of the threephases.

– Taps for one or twophases run off themainline downsidestreets

At the House• At each house, there is a

transformer drum attached tothe pole.

• In subdivisions, the lines areoften underground, with agreen transformer box aboveground.

• Transformer reduces 7200volts down to 240 volts.

• The 240 volts entersa house through atypical watt-hourmeter.

• The meter lets thepower companycharge you forenergy use.

• Single-phase power– What you have in

your houses– Single-phase 120-

volt AC service– 1 prong delivers

electrons toappliance

– 1 prong deliverselectrons to theground.

85% fromfossil fuels

• 1._______________• 2._______________• 3._______________• 4._______________• 5._______________

• 1. Power plant– Generator, Steam

Turbine• 2.Transmission

Substation• 3.Power Substation• 4.Transformer Drum• 5.Tap

Threat Article

• Read/ Debate?

Final Announcements

• Have a great weekend.

• Don’t forgot it is Mother’s Day onSunday.