INTO THE GRID A Study of the Power Grid

THE BIG PICTURE The 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. http://people.howstuffworks.com/blackout.htm

THE BIG PICTURE Power travels from the power plant to your house through an amazing system called the power distribution grid. http://people.howstuffworks.com/blackout.htm

HOW DOES A BLACKOUT OCCUR? POWER PLANT TRIPS OFF LINE Lightning Strike, fire When 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 FAILURE Lightning/Sagging When 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.

SMALLER PICTURE WHAT HAPPENS WHEN YOU PLUG IN THE TOASTER????

CIRCUITS Behind the outlets in our home is a series of complex circuits A circuit is simply a closed loop through which charges can continuously move http://www.glenbrook.k12.il.us/gbssci/phys/Class/circuits/u9l1b.html

CIRCUIT REQUIREMENTS There 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, http://www.glenbrook.k12.il.us/gbssci/phys/Class/circuits/u9l1b.html

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 on 1) Electric charge - a property of the object experiencing the electrical field, 2) Distance from source - the location within the electric field Charges will move from high to low electric potential http://www.glenbrook.k12.il.us/gbssci/phys/Class/circuits/u9l1b.html

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 http://www.glenbrook.k12.il.us/gbssci/phys/Class/circuits/u9l1c.html

VOLTAGE In 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. http://www.glenbrook.k12.il.us/gbssci/phys/Class/circuits/u9l1b.html

CURRENT Current is the rate at which charges flow past a point in a circuit. Current is charge transfer per unit time CURRENT = CHARGE/TIME The standard metric unit for current is the ampere 1 ampere = 1 coulomb / 1 second

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

RESISTANCE Resistance is the hindrance to the flow of charge Devices within a circuit( light bulb, toaster,etc.) offer resistance to the current The standard metric unit for resistance is the ohm, represented by the Greek letter omega -

OHM’S LAW the 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

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 toaster The toaster itself offers resistance to the flow of current (so too does the plug of the toaster)

POWER Electrical 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 watt P = IV P = power in watts I = current in amperes V = voltage in volts

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

ENERGY Electric Energy is a measure of the amount of power that is consumed in a certain amount of time Energy = Power x time Energy is measured in a quantity known as kilowatt hours You are charged for the amount of kilowatt hours you consume

Quantity Symbol Equation(s) Standard Metric Unit Other Units Potential Difference (a.k.a. voltage)   V      V = I • R Volt (V) J / C Current I I = Q / t I =   V / R Amperes (A) Amps or C / s or V /    Power P P =   E / t P=IV P=I2R P=V2/R Watt (W) J / s Resistance R R =   V / I Ohm (   ) V / A Energy E or   PE   E = P • t Joule (J) V • C or W