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Electricity In Your House

1 Without even thinking we can flip a switch and have light at any hour of the day or night. We can even choose what temperature we prefer in our house simply by adjusting a thermostat. All of this thanks to electricity. Few of us, though, know where this power comes from and how exactly it makes it to our house.

2 We all remember Benjamin Franklin’s famous kite experiment where he discovered that lightning was in fact electricity. However, electricity doesn’t just come from lightning. Today there are several methods of generating electricity from hydroelectric dams, gas turbines and diesel engines.

Image courtesy of How Stuff Works

3 In most cases coal and oil are burned to generate steam which is used to turn a turbine which then spins a generator. As the coil turns inside the generator, a permanent external magnetic field induces an alternating current (AC) of electricity in the coil.

Image courtesy of solcomhouse

Image courtesy of EnergyQuest

Image courtesy of EnergyQuest

4 Alternating current is a back and forth movement of electrons. AC electricity is the opposite of DC or direct current electricity, which is a unidirectional flow of electrons. This type of circuit operates in a flashlight or calculator that uses batteries as a power supply. After Thomas Edison first invented the light bulb all of the power in the United States was created by DC generators. However, Nikola Tesla found that AC power had some significant advantages. To begin with, it is more efficient and less expensive  to produce than DC power since large electric generators produce AC naturally. Secondly, high voltage, high current DC is more dangerous to use. And finally, through the use of transformers, AC can easily be changed to higher or lower voltages. In fact, the voltage of AC electricity is changed many times during its delivery to your house.

Image courtesy of How Stuff Works

5 AC power, therefore, is very important for power delivery. As seen in the diagram above when power initially leaves the power plant it is sent to a transmission substation where it is initially raised to voltages ranging anywhere between 155,000 to 765,000 volts for it to travel as far as 300 miles. After power leaves the transmission substation it is sent through the transmission grid, or the series of "towering giants" we often see along the side of the road.
6 Power transmission must obey one of the fundamental laws of physics, conservation of energy. This law states that within a closed system, energy can not be created or destroyed, just changed in form. Power is the rate at which energy is created or used: power x time = energy. Once the power plant produces the "electricity" the power being transmitted is limited to an initial value that needs to remain maximized during transmission. One important formula for electricity is: power = current x voltage. Consequently power is transmitted at the highest possible voltage to minimize current. Low currents also help reduce energy losses to heat in the wire since power lines use low gauge, large diameter, multi-stranded wires. This resistance is reduced by using low gauge, or large diameter, multi-stranded wires.
7 When power arrives at power substations its voltage is reduced to 7,200 volts. It is also at these power substations that the power is stepped down for shorter distance travel and can be split for distribution by a “bus” that redirects power in different directions - for example, multiple subdivisions or parts of a city.

Image courtesy of How Stuff Works

8 Another feature along power lines are regulator banks. Regulators make sure that the voltage in the wire stays consistent. In the picture below there are three switches near the top of the apparatus that allow it to be disconnected for maintenance and necessity. Before power can arrive at your house it must be stepped down one more time. This is why there is a transformer drum at the junction where power is delivered to your house which requires 240 volts of electricity for things to operate.

Image courtesy of How Stuff Works

Image courtesy of How Stuff Works
9 Finally, power has traveled from the generator at the power plant, to the transmission substation, through the power grid, into the power substation and finally through the transformer into your home. Not a bad effort from your power company who is sending thousands of volts hundreds of miles everyday!
10 On a larger scale, these systems of power generation, transmission and distribution are all interconnected in a single network which is often incorrectly referred to as the "national power grid." This gigantic network is divided into three subdivisions: the Eastern Interconnect, the Western Interconnect, and the Texas Interconnect. All distribution lines within the country, as well as Mexico and Canada, are interconnected allowing power companies to share resources.

Image courtesy of solcomhouse

11 This governing system maintains power when local plants must either lower their input or when one area has a particularly high need. On the other hand this high level of connection can lead to problems. If a series of plants go out during a time of high need, it becomes difficult to maintain a consistent voltage in the power lines. These erratic voltages can cause high heat making power lines sag and causing equipment damage. So, many plants will switch out of the grid in a domino-like cascade to avoid equipment damage. In the past, huge blackouts have covered the entire Northeast (1965, 1977, 2003) and Northwest (1996).
12 So after power has arrived in your home, how much does it actually cost you to use it? You purchase energy from your local power company in a unit called a kilowatt-hour. So what is a kilowatt-hour? To explain, we must remember that power x time = energy. In this formula, power is measured in kilowatts or 1000's of watts, and time is measured in hours. So a kilowatt-hour (kwh) represents an energy usage of 1000 watts of power each hour. The meter on the side of your house records for the power company the amount of energy, or  kilowatt-hours, your family consumes each month.

Image courtesy of How Stuff Works

13 Let’s take a look at what electricity costs the average family. Suppose you run a 100 watt light bulb (100 watts equals 100/1000 = 0.1 kilowatts) in a lamp next to your desk for 4 hours each day, 30 days a month. That means it operates for a total of 120 hours a month. This represents an energy consumption of 0.1 kilowatts x 120 hours or 12 kwh. Well, on average electricity in Florida, it costs $0.08 per kilowatt-hour. So it would cost $0.08 x 12 or  $0.96 or roughly one dollar a month to use your desk lamp. Even though this seems cheap, seven or eight light bulbs can add up. A color TV however cost slightly more. If a TV is left on 8 hours a day it will cost $4.80 a month. That’s about two cents an hour for entertainment - a lot better than $8/person for the movies.
14 In Florida, air conditioning and ceiling fans are crucial. A ceiling fan is the cheapest way to stay cool. It will only cost about $1.92 a month. Air conditioning costs, on the other hand, can vary greatly depending on the size and design of the house, but it is not uncommon for them to consume $100 worth of electricity a month. There can be some major differences depending on where you live. If you are unsure how much you are paying per kwh take the total amount you paid on your monthly bill and divide it by the total number of kilowatt-hours you used.

Other Typical Utility Costs per month in Florida
Dishwashers and Electric Ovens $3.00
Clothes Dryers$4.80
Water Heaters$25.00
Data provided by FPL

General Questions

If leaving a color TV on for 8 hours a day will cost $4.80 a month (30 days), how many hours of TV can be watched in one month to be equivalent to going to an $8 movie that lasts two hours?

In Paragraphs 12 and 13, there are two formulas given. One is for energy (power x time= energy) and the other is cost for electricity (energy x rate = cost). Lets use both of these to solve the following:

If it costs $4.80 to run your television for 8 hours a day for a month (30 days) how many kilowatts does your television use if power costs $.08 per kwh?

In your house you have lights, AC, washer and dryer, a TV, a water heater and a refrigerator. Your electric bill for the month is $126.00 not including taxes. You figured out that the cost of lighting was $8.00, air conditioning was $42.00, washing and drying clothes was $4.00 and watching TV was $6.00 How much was it to run the water heater if it costs twice as much to run the water heater as it does to run the refrigerator?

At one time, homes were powered by direct current (DC) rather than with alternating current (AC). Which statement is about direct current is FALSE?

A huge boom is heard during a storm, signaling that a transformer has blown on the power pole down the street. What is the purpose of the transformer?

T Hales

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