2 THE BIG PICTUREThe power grid is a very simple thing. It consists of a set of large power plants (hydropower plants, nuclear power plants, etc.) all connected together by wires. One grid can be as big as half of the United States.
3 THE BIG PICTUREPower travels from the power plant to your house through an amazing system called the power distribution grid.
4 HOW DOES A BLACKOUT OCCUR? POWER PLANT TRIPS OFF LINELightning Strike, fireWhen that plant disconnects from the grid, the other plants connected to it have to spin up to meet the demand. If they are all near their maximum capacity, then they cannot handle the extra load. To prevent themselves from overloading and failing, they will disconnect from the grid as well. That only makes the problem worse, and dozens of plants eventually disconnect. That leaves millions of people without power.TRANSMISSION LINE FAILURELightning/SaggingWhen that transmission line failed, all of its load shifted to neighboring transmission lines. They then overloaded and failed, and the overload cascaded through the grid.In nearly every major blackout, the situation is the same. One piece of the system fails, then the pieces near it cannot handle the increased load caused by the failure, so they fail. The multiple failures make the problem worse and worse and a large area ends up in the dark.
5 SMALLER PICTUREWHAT HAPPENS WHEN YOU PLUG IN THE TOASTER????
6 CIRCUITSBehind the outlets in our home is a series of complex circuitsA circuit is simply a closed loop through which charges can continuously move
7 CIRCUIT REQUIREMENTSThere must be a closed conducting path which extends from the positive terminal to the negative terminal.There must be an electric potential difference across the two ends of the circuit. This is can be established by the use of a battery or generator,
8 ELECTRIC POTENTIAL DIFFENERENCE VOLTAGE Gravitational potential energy is dependent on mass and location. The boulder on the right will move from an area of high gravitational potential energy to an area of low gravitational potential energy when dropped.Electric potential energy is dependent on1) Electric charge - a property of the object experiencing the electrical field,2) Distance from source - the location within the electric fieldCharges will move from high to low electric potential
9 Electric Potential Difference Voltage Electric potential difference is the difference in electric potential (V) between the final and the initial location when work is done upon a charge to change its potential energy.Electric Potential difference or voltage is measured in a unit known as the volt
10 VOLTAGEIn a battery the chemical energy produced by the reaction of the chemicals inside the battery is used to do work on a positive test charge to move it from the low potential terminal to the high potential terminal. Once at the high potential terminal, a positive test charge will then move through the external circuit and does work upon the light bulb or the motor or the heater coils, transforming its electric potential energy into useful forms for which the circuit was designed. The positive test charge returns to the negative terminal at a low energy and low potential, ready to repeat the cycle (or should we say circuit) all over again.
11 CURRENTCurrent is the rate at which charges flow past a point in a circuit.Current is charge transfer per unit timeCURRENT = CHARGE/TIMEThe standard metric unit for current is the ampere1 ampere = 1 coulomb / 1 second
12 ALTERNATING AND DIRECT CURRENT DIRECT CURRENT (DC)the continuous movement of electrons from an area of negative (-) charges to an area of positive (+) charges through a conducting material such as a metal wire..Such a circuit consists of a source of electrical energy (such as a battery) and a conducting wire running from the positive end of the source to the negative terminal.Alternating Current (AC)the type of electricity commonly used in homes and businesses throughout the world. the current alternates in direction, back-and-forth between 50 and 60 times per second. AC is created by an AC electric generator
13 RESISTANCE Resistance is the hindrance to the flow of charge Devices within a circuit( light bulb, toaster,etc.) offer resistance to the currentThe standard metric unit for resistance is the ohm, represented by the Greek letter omega -
14 OHM’S LAWthe electric potential difference between two points on a circuit ( V) is equivalent to the product of the current between those two points (I) and the total resistance of all electrical devices present between those two points (R).V = I • R
15 SO WHAT HAPPENS WHEN YOU PLUG IN THE TOASTER? The outlet supplies the voltage necessary to move the charge (AC current) In the US typical household voltage is 120V. That voltage is actually created in a power plant somewhere else and then delivered to your house by the power wires that are on poles or buried underground.The wires of the toaster conduct the current through the toasterThe toaster itself offers resistance to the flow of current (so too does the plug of the toaster)
16 POWERElectrical power is the rate at which electrical energy is supplied to a circuit or consumed by a load. It is the product of voltage and current.Power is measured in a unit known as the wattP = IVP = power in wattsI = current in amperesV = voltage in volts
17 POWER P = IV P=I(IR) P=I2•R P=IV P=(V/R) V P = V2 / R USING OHM’S LAW WE CAN DERIVE TWO NEW EQUATIONS FOR POWER
18 ENERGYElectric Energy is a measure of the amount of power that is consumed in a certain amount of timeEnergy = Power x timeEnergy is measured in a quantity known as kilowatt hoursYou are charged for the amount of kilowatt hours you consume
19 QuantitySymbolEquation(s)Standard Metric UnitOther UnitsPotential Difference(a.k.a. voltage) V V = I • RVolt (V)J / CCurrentII = Q / tI = V / RAmperes (A)Amps or C / sor V / PowerPP = E / tP=IVP=I2RP=V2/RWatt (W)J / sResistanceRR = V / IOhm ( )V / AEnergyE or PE E = P • tJoule (J)V • C orW