THE ELECTRICAL  POWER GRID

THE ELECTRICAL POWER GRID

We have been talking now for so one about electricity and the fact that if we need to update the urgent networks m th grid, the transmission and substations it will costs 100 of Trillion Dollars or Euros only to update the GRID. If in addition to the arrival of new electrical equipment in the market including the Million of EV′s on a daily bases our current Electricity generation plants and the network Grids and substations are not ready to replace what has existed for the past 100 years.

Electrical power is a little bit like the air you breathe: You don't really think about it until it is missing. Power is just "there," meeting your every need, constantly.

It's only during a power failure, when you walk into a dark room and instinctively hit the useless light switch that you realize how important power is in your daily life.

You use electrical power for?heating, cooling, cooking, refrigeration, light,?sound,?entertainment, computers, mobile devices and maybe even your car. Without power, life as we know it doesn't exist.

Electrical power travels from the power plant to your house through an amazing system called the?power distribution grid. The grid is quite public — if you live in a suburban or rural area, chances are it is right out in the open for all to see. It is so public, in fact, that you probably don't even notice it anymore. Your?brain?likely ignores all of the power lines because it has seen them so often.

Although most of us take the power grid for granted, it's anything but simple. There are 450,000 miles (724,205 kilometers) of high-voltage power lines and 160,000 miles (257,500 kilometers) of overhead transmission lines in the United States connecting electrical power plants to homes and businesses [source:?DOE]. Since large amounts of energy cannot be stored, electricity must be produced as it is used [source:?EIA]. The power distribution grid must respond quickly to shifting demand and continuously generate and route electricity to where it's needed the most.

The power grid is also evolving. Upgrades in technology now let us connect our own home-generated electricity to the grid — using solar panels or wind generators — and get paid back by utilities. The U.S. federal government is also investing in a so-called?smart grid?that employs digital technology to more efficiently manage energy resources. The smart grid project also will extend the reach of the grid to access remote sources of renewable energy like geothermal power and wind farms [source:?DOE].

In this article, we will look at all of the equipment that brings electrical power to your home and what kinds of glitches can cause a blackout.

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EUROPEAN POWER STATIONS AND NETWORK
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US POWER GENERATION PLANTS NETWORK


Electrical power starts at the power plant. In almost all cases, the power plant consists of a?spinning electrical generator. Something has to spin that generator — it might be a water wheel in a hydroelectric dam, a large?diesel engine or a gas turbine. But in most cases, the thing spinning the generator is a?steam turbine. The steam might be created by burning coal, oil or natural gas. Or the steam may come from a?nuclear reactor.

Electricity generation is the single largest source of our welfare state,that's why it's so important to develop more renewable sources of energy. In 2014, 67 percent of America's electricity came from fossil fuels like coal and natural gas. Hydroelectric energy was the largest renewable energy source, followed by solar, wind and geothermal power. In 2014, 6 percent of America's electricity was produced by hydropower, while solar, wind and thermal energy?together?comprised another 5 percent [source:?EIA].

No matter what energy source spins the generator, commercial electrical generators of any size generate what is called?3-phase AC power. To understand 3-phase AC power, it is helpful to understand single-phase power first.

The Power Plant: Alternating Current

Single-phase power?is what you have in your house. You generally talk about household electrical service as single-phase, 120-volt AC service. If you use an oscilloscope and look at the power found at a normal wall-plate?outlet, what you will find is that the power at the wall plate looks like a?sine wave, and that wave oscillates between -170 volts and 170 volts. The peaks are indeed at 170 volts; it is the effective (rms) voltage that is 120 volts.

The rate of oscillation for the sine wave is 60 cycles per second. Oscillating power like this is generally referred to as AC, or?alternating current. The alternative to AC is DC, or?direct current.?Batteries?produce DC: A steady stream of electrons flows in one direction only, from the negative to the positive terminal of the battery.

AC has at least three advantages over DC in a power distribution grid:

  1. Large electrical generators happen to generate AC naturally, so conversion to DC would involve an extra step.
  2. Transformers must have alternating current to operate, and we will see that the power distribution grid depends on transformers.
  3. It is easy to convert AC to DC but expensive to convert DC to AC, so if you were going to pick one or the other AC would be the better choice.

The power plant, therefore, produces AC. On the next page, you'll learn about the AC power produced at the power plant. Most notably, it is produced in three phases.

The Power Plant: Three-phase Power

The power plant produces three different phases of AC power simultaneously, and the three phases are?offset 120 degrees?from each other. There are four wires coming out of every power plant: the?three phases?plus a neutral or?ground?common to all three.

Why three phases? Why not one or two or four? In 1-phase and 2-phase power, there are 120 moments per second when a sine wave is crossing zero?volts. In 3-phase power, at any given moment one of the three phases is nearing a peak. High-power 3-phase motors (used in industrial applications) and things like 3-phase welding equipment therefore have even power output. Four phases would not significantly improve things but would add a fourth wire, so 3-phase is the natural settling point.

And what about this "ground," as mentioned above? The power company essentially uses the earth as one of the wires in the power system. The earth is a pretty good conductor and it is huge, so it makes a good return path for electrons. (Car manufacturers do something similar; they use the metal body of the car as one of the wires in the car's electrical system and attach the negative pole of the battery to the car's body.) "Ground" in the power distribution grid is literally "the ground" that's all around you when you are walking outside. It is the dirt, rocks, groundwater and so on of the earth.

The Transmission Substation


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THE POWER TRANSMISSION NETWORK


The three-phase power leaves the generator and enters a?transmission substation?at the power plant. This substation uses large transformers to convert or "step up" the generator's voltage to extremely high voltages for long-distance transmission on the transmission grid. Typical voltages for long distance transmission are in the range of 155,000 to 765,000 volts. The higher the voltage, the less energy is lost due to resistance [source:?UCSUSA].

A typical maximum transmission distance is about 300 miles (483 kilometers). High-voltage transmission lines are quite obvious when you see them. They are huge steel towers strung out in a line that stretches toward the horizon.

All high-voltage towers have three wires for the three phases. Many towers also have extra wires running along the tops of the towers. These are ground wires and are there primarily in an attempt to attract?lightning.

The Power Distribution Grid

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POWER STATION


For power to be useful in a home or business, it comes off the transmission grid and is?stepped-down?to the distribution grid. This may happen in several phases. The place where the conversion from "transmission" to "distribution" occurs is in a?power substation. A power substation typically does two or three things:

  • It has transformers that "step down" transmission voltages (in the tens or hundreds of thousands of volts range) down to distribution voltages (typically less than 10,000 volts).
  • It has a "bus" that can split the distribution power off in multiple directions.
  • It often has circuit breakers and switches so that the substation can be disconnected from the transmission grid or separate distribution lines can be disconnected from the substation when necessary.

The power goes from the transformer to the?distribution bus. The bus distributes power to local distribution lines. The bus has its own transformers that can also step down or step up voltage according to local energy needs.

At the bus, there may be two separate sets of distribution lines at two different voltages. Smaller transformers attached to the bus step the power down to standard line voltage (usually 7,200 volts) for one set of lines, while power leaves in the other direction at the higher voltage of the main transformer.

The next time you are driving down the road, you can look at the power lines in a completely different light. On a typical utility pole, the three wires at the top of the poles are the three wires for the 3-phase power. The fourth wire lower on the poles is the ground wire. In some cases there will be additional wires, typically?phone,?cable TV?or Internet lines riding on the same poles.

Lines that carry higher voltage will need to be stepped down further before entering residential buildings and most businesses. This often happens at another substation or in small transformers somewhere down the line. For example, you will often see a large green box (perhaps 6 feet or 1.8 meters on a side) near the entrance to a subdivision. It is performing the step-down function for the subdivision.

The Regulator Bank

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You will also find regulator banks located along the line, either underground or in the air. Above-ground regulator banks look like three garbage can-sized transformers held up by two utility poles. They regulate the voltage on the line to prevent undervoltage and overvoltage conditions. The regulator bank works to maintain a steady 7,200 volts running through the neighborhood on three wires (with a fourth ground wire lower on the pole).

Most homes and businesses only need single-phase power, so typically you will see three wires running down a main road, and?taps?running off on side streets. The taps on utility poles can be configured to deliver single-phase or two-phase power to residences and commercial buildings.

Generating Power to Your House

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Delivery of Eectricity to homes


And finally we are down to the wire that brings power to your house! Past a typical house runs a set of poles with one phase of power (at 7,200 volts) and a ground wire (although sometimes there will be two or three phases on the pole, depending on where the house is located in the distribution grid). At each house, there is a?transformer drum?attached to the pole.

In many suburban neighborhoods, the distribution lines are?underground?and there are green transformer boxes at every house or two.

The transformer's job is to reduce the 7,200 volts down to the?240 volts?that makes up normal household electrical service. Let's look at this pole one more time, from the bottom, to see what is going on:

  • Note there is a bare wire running down the pole. This is a grounding wire. Every utility pole on the planet has one. If you ever watch the power company install a new pole, you will see that the end of that bare wire is stapled in a coil to the base of the pole and therefore is in direct contact with the earth, running 6 to 10 feet (1.8 to 3 meters) underground. It is a good, solid ground connection. If you examine a pole carefully, you will see that the ground wire running between poles (and often the guy-wires coming from the sides) are attached to this direct connection to the ground.
  • There are two wires running out of the transformer and three wires running to the house. The two from the transformer are insulated, and the third one is bare. The bare wire is the ground wire. The two insulated wires each carry 120 volts, but they are 180 degrees out of phase so the difference between them is 240 volts. This arrangement allows a homeowner to use both 120-volt and 240-volt appliances. The transformer is wired in this sort of configuration:


The 240 volts enters your house through a?watt-hour meter, which measures your electrical consumption so the power company can charge you for putting up all of those wires. In the past, meter readers would periodically check your meter to record your usage. As part of the national upgrade to?smart grid?technology, millions of residential meters have now been replaced with?smart meters?that communicate directly with the power company. Not only can the utility read your meter remotely, but it is notified instantly in the case of a power outage, speeding recovery time [source:?DOE].

Safety Devices: Fuses

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HOME FUSES


Fuses?and?circuit breakers?are?safety devices. Let's say that you did not have fuses or circuit breakers in your house and something "went wrong." What could possibly go wrong? Here are some examples:

  • A fan?motor?burns out a bearing, seizes, overheats and melts, causing a direct connection between power and ground.
  • A wire comes loose in a lamp and directly connects power to ground.
  • A mouse chews through the insulation in a wire and directly connects power to ground.
  • Someone accidentally vacuums up a lamp wire with the?vacuum cleaner, cutting it in the process and directly connecting power to ground.
  • A person is hanging a picture in the living room and the nail used for said picture happens to puncture a power line in the wall, directly connecting power to ground.

When a 120-volt power line connects directly to ground, its goal in life is to pump as much electricity as possible through the connection. Either the device or the wire in the wall will burst into flames in such a situation. (The wire in the wall will get hot like the element in an electric oven gets hot, which is to say very hot!).

A?fuse?is a simple device designed to overheat and burn out extremely rapidly in such a situation. In a fuse, a thin piece of foil or wire quickly vaporizes when an overload of current runs through it. This kills the power to the wire immediately, protecting it from overheating. Fuses must be replaced each time they burn out, which is why very few homes still use them.

A?circuit breaker?uses the heat from an overload to trip a switch, and circuit breakers are therefore resettable. Power enters the home through a?circuit breaker panel. Inside the?circuit breaker panel?are two primary wires from the transformer entering the?main circuit breaker?at the top. The main breaker lets you cut power to the entire panel when necessary. Within this overall setup, all of the wires for the different outlets and lights in the house each have a separate circuit breaker or fuse.

If the circuit breaker is on, then power flows through the wire in the wall and makes its way eventually to its final destination, the?outlet.

Grid-Connected Renewable Energy Systems

If you live in states like Arizona, New Mexico and Nevada, or in sunny Southern Spain, Greece or Southern Italy it pays to have?solar panels. These countries and cities averages more than 3,800 hours of sunshine each year. In the past, if you wanted to generate your own power using renewable resources like solar panels or wind turbines, you would have to operate "off the grid" — disconnected from the power grid run by your local electrical utility.

Now, thanks to upgrades in technology and changes in policy and regulations, most states and utility companies allow individuals to generate their own power and remain linked with the larger grid.

How does it work? Armed with a special electrical meter and some current inversion equipment, homeowners can tap renewable resources like sunshine and wind to supplement the electricity they receive from the grid. If it's a cloudy day , folks with grid-connected homes don't have to read in the dark. They can use as much or as little electricity from the main grid as they want.

Even better, if homeowners are able to generate more power than they need, the local utility will buy the excess power from them, essentially "turning back the meter" [source:?DOE].

Home Battery

One drawback of traditional grid-tied solar energy systems is that consumers use most of their electricity in the morning and evening, while solar power production peaks in the middle of the day. In essence, homeowners sell their daytime energy to the utility and buy it back at night. Batteries at th moment are very expensive and the lifetime of these is limited.

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ELECTRICITY BACK UP BATTERIES


Sources; Department of Energy(DOE) Eumonitor, Sciencedirect, Visual Capitalist, European Energy Exchange(EEX), Enel, Endesa, Iberdrola, Scottish Power, Electricite de France (EDF).

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