- Education and Science
The Electricity Guy: Back To Basics
Power Up: Making Electricity
It is something we now all take for granted until it is no longer there. Electricity.
Of course, electricity does not just happen. It has to be made somewhere.
It all starts at the generator plant.
A generator works by turning a magnet in the center of a series of coiled copper.
The spinning magnet creates a field in the coiled copper, and the result is electricity.
A turbine is used to spin the magnet.
There are several different ways to power the turbine.
Steam: Steam-powered turbines are common. The steam is created using many different methods. The most modern way is with a nuclear reactor. Although this method is controversial with many siting safety issues. Some older methods still in use but also controversial due to environment concerns are, coal, oil, and natural gas.
Hydro-electric: Another common way to generate electricity, and the least controversial is hydro-electric. This is the preferred way of generating electricity in Canada, as it is clean and renewable. Often a dam is used to create a waterfall, or in some cases an actual waterfall is used. Niagara Falls generates electricity for millions of users every day.
Wind and Solar: Wind generators and solar panels are now becoming more common. Although, there have been concerns about the wind mills as they are ugly and it has been noted that the blades often kill birds. The solar panels are a better option, but so many are required to produce an adequate amount of electricity to be useful. They also take up a lot of room.
It's the Law, Ohm's Law, That Is
The very basic calculation for anything electrical is Ohm's Law.
Before Ohm's Law can be explained, an understanding of the three basic components that make up Ohm's Law is required.
Electrical Pressure measured in volts (V), is a calculation of how much force is behind an electrical current. A high voltage is required to carry electricity over long distances (discussed later).
Electrical Intensity measured in amperes (A) or amps for short, is the amount of electricity. Every electrical device is rated for a specific amount of electricity. If too much electricity (too many amps) goes through an electrical device, it will begin to get hot. This is called an overload. This is the cause of electrical fires. Although, there are many different factors that can cause an overload, and will be discussed later.
Resistance measured in ohms (Ω), is the amount of resistance against an electrical current by a specific material. Some materials such as plastic, rubber, glass, oil, and water* have a very high resistance to electricity to the point where the electricity can hardly flow at all. Other materials such as copper, aluminum, steel, and sodium have a very low resistance to the point where electricity can flow very freely and easily through these materials. Organic materials such as human skin and flesh actually react with electricity so that the resistance lowers as voltage increases (discussed later).
*Pure water without impurities (distilled water) does not conduct electricity. Electricity is conducted through water by metal particles and minerals in the water.
Knowing the three basic components, you can now use Ohm's Law.
The Ohm's Law triangle (below) is commonly used. You just simply comer up the one you don't know and use the other two to calculate.
OHM'S LAW: V (volts) = I (amps) multiplied by R (ohms)
Example: A toaster draws 10 amps at 120 volts. You divide the amps from the volts, 120 / 10 = 12. The resistance of the toaster is 12 ohms.
AC/DC, Not the Band
Electricity can flow in a single direction all the time (DC), or in alternating directions several time per second (AC).
Electricity supplied by the generating station to you is AC (alternating current). Due to the fact that the magnet in the generator is turning, it creates a negative and positive flow of electricity. This creates a sine-wave (a positive peak, a negative dip, and a neutral). Depending on where you are in the world this alternation can happen either 50 or 60 times per second. It is typically 60 times per second in North America, and 50 in most places in Europe.
AC flow is better for devices such a motors. Since a motor is really just the opposite of a generator. In a motor, the electricity goes into the copper coils to create a magnetic field that turns the motor.
Batteries supply DC (direct current). DC only flows one way, from negative to positive. DC flow is better for electronic equipment. Electronics that can be plugged into an AC outlet use a device called a bridge rectifier to change the AC into DC (discussed in another entry).
Move It: Getting Electricity From the Generator To You
When electricity leaves the generator, the voltage is not high enough to transmit over a great distance. Therefore a transformer is used to increase the voltage (transformers will be discussed in more detail in another entry).
In the last paragraph, I mentioned the sine-wave with the positive, negative, and neutral. These are called phases, and it is the reason why you always see three sets of wires to carry electricity. Have you ever noticed that? High-voltage transmission lines always carry wires in multiples of three. Six is very common, but I have seen as many as 18 in some tower monstrosities. Each set of three wires is one circuit with three phases each. At any time during the cycle (60 or 50 times per second), one wire has a positive voltage (V+), one has a negative voltage (V-), and the third is neutral (no voltage). This continues through the whole system (electrical grid) until it gets to you. Unfortunately, you only get one phase of the cycle. Three-phase cycles are only delivered to industrial, medical, and broadcasting applications. Your home and office only get a single-phase of what is commonly known as 'dirty' electricity. This was done at the turn of the (last) century for economical reasons because at that time there were not really any devices used in a home that required 'clean' electricity. Now with more electronics used in the home and office, a three-phase cycle would be better, but would be too expensive to change now. Equipment requiring 'clean' electricity such as a computer have a built-in power supply that smooths-out the current into the device.
Transmission lines generally have voltages ranging from 100,000 up to about 750,000 for most places in North America. However, China is currently experimenting with a two million volt transmission grid. The problem with such a high voltage grid is that the wires would have to be very far apart and very high off the ground. Plus, the grid could not be close to any populated areas.
Once the transmission gets to its destination, the voltage can be reduced and sent out on poles as feeders. This is done at a transformer station. The feeder lines are about 20,000 volts, and are usually at the top of standard poles, but are now sometimes seen on their own poles.
20,000 volts is too high for use at the consumer end, so before the electricity can be input to you, it must again have its voltage reduced. Another set of transformers located on the poles, but also sometimes underground, are used to bring the voltage to the local service voltage (about 120 volts in North America). This time the output is only a single phase, with the other phases shared with your neighbors.
Electricity Is Lazy
Electricity always wants to take the shortest path home, the easiest path, or to the ground.
However, this is not a good thing as it will allow an infinite amount of electricity to flow. This is called an overload, and will almost always start a fire.
Faults in electrical devices can cause a ground fault (electricity can flow directly to the ground), or a short-circuit (electricity is allowed to flow through a very low resistance load).
Modern electrical systems have many built-in safety features to help avoid this. Ground-fault interrupters, circuit breakers, and fuses are just a few devices used to keep electricity safe and under control.
For those living in the north-eastern United States and southern parts of Canada may remember the big blackout of August 14, 2003. That was an example of how the safety systems worked together to prevent a major catastrophe. A ground fault in Ohio caused all connected systems to cut circuits all the way to central Ontario.
A major inconvenience, but it saved millions of dollars of electrical equipment from damage.
Keeping Yourself Safe
Below is a photo of a meter indicating the resistance of my own body as measured across both arms. That number is in mega-ohms. A very high resistance.
However, as I mentioned before, organic matter is not the same as a fixed electronic device. Organic matter works with electricity so that as voltage increases, the resistance decreases.
That reading on the meter is based on the 1.5 volts supplied by the meter for testing. That will drop considerably as the voltage goes up. At the local supply voltage, enough current can be pushed through a human to cause serious injury or worse.
Always respect electricity. Don't open electrical appliances or experiment with electricity in any way if you do not know what you are doing. Stay way from transformer stations and power lines.
That is all for this entry from 'The Electricity Guy'.
More electricity and electronics articles soon.