What is the voltage of eletricity when it comes out of an eletric plant?

Question

I heard that electricity comes out of a hidroplant with a much higher voltage than what we use at home. How do they lower the voltage? Is there wasted eletricity (energy) in the process?

Thanks for helping me understand this.

Answer 1

The voltage can reach levels of over 500,000 volts when it comes out of an eletric plant.

The high voltage electric current travels through transmission lines. A second set of wires is used to carry the current back to the generator. These wires are there because electric current travels in a closed circuit. High-voltage substations are places where very high voltages are reduced to lower levels. High-voltage power lines enter and leave the transformer through large insulators. These insulators are used to keep the high voltages away from the metal tank containing the transformer coils. Oil flows around the coils to keep them cool.

The electricity now travels from the substations to transformers in your neighborhood. These transformers, called "Step-Down Transformers," lower the voltage still further to make the voltage safe for ordinary use in your home. Inside these transformers are coils of wire which help reduce the voltage to 120/240 volts which then can be used safely in homes.

There is no energy wasted along the process. Remember that energy cannot be destroyed but can be transformed. There is no transformation of energy on the process thus it is not wasted.☺

Answer 2

The electricity coming from a power generating facility is created (if I can use that term) by rotating an electric machine with a prime mover (waterwheel, steam turbine, etc). The limitation on the voltage at the machine terminals is a function of insulating materials and internal clearances. It also depends on the facility itself ... for a large utility, the voltage at the generator terminals will be 13.2 kV - 35 kV (some voltages are more common in North America than elsewhere, which is why the range). Similar facilities, like cogeneration plants or electric generators inside large manufacturing plants will be 6 kV - 15 kV.

Once the line leaves the generating "area" (in the case of a large utility, that means the main building), it passes through a transformer to "step up" the voltage to transmission levels. This may go as high as 750 kV - or possibly higher, depending on the region and the length of transmission. Higher voltages are chosen where the distribution is lengthy, because the "losses" in transmission are proportional to current. Since power = voltage * current, reducing the loss component makes sense.

As the power is brought into places where it can be used, it is "stepped down" by another transformer to the level used on that distribution network. For example, a large city might have several main branches at 15 kV to service its industrial consumers and a large number of 2300 - 4160 V lines to service its residential load.

The voltage is further stepped down by another transformer at the point where the line becomes the responsibility of the consumer (just outside the wall for an industry, and at the pole for a residence). Industry will generally only go down to 600 V - many stay as high as 4160. Residences tend to be reduced to the "outlet voltage" ... 120 in North America, 240 in Europe, etc.

There is some loss of energy in the process - no transformer is 100 percent efficient. But most are better than 98.5 (some are 99.5 or more!). However, the loss is proportional to the current on the incoming (high voltage) side ... so it's negligible compared to everything on the downstream (consumer) side.

I am assuming that you know how a trasnformer works, of course. If you need help with that, send me a message.

Answer 3

Power losses are low when electricity in the form of Alternating Current (AC) is transmitted at high voltages. This is the reason why we have high tension lines to carry electricity over large distances. At each power plant (no matter what type), there are Step-up transformers which do exactly what their name says: to step up the voltage (and lower the current, of course) to a fixed transmission value. Before using this electricity, it has to be stepped down to la ower household voltage (it is 230V in India, no idea abt others) and guess using what? A step down transformer. There is small amount of loss (mainly as heat in transformer coils) in both step up and down processes but it is much less than what you will have by direct transmission. You should read a bit about transformers if you dont already know, atleast the principle of operation!

Answer 4

I don't know the exact voltage, but it isn't as high as you think it might be. I believe just a few hundred volts.
But to transport the electricity, a transformer is used to jack the voltage up to around 50,000 volts. The equation V = I R comes into play. The resistance stays the same so V / I = R. The voltage goes way up so the amperage has to come way down. They do this to prevent hysteresis loss. the loss of energy due to the friction thru the wires heat up; These are V = I^2 R losses. So V / I^2 = R. Since the I^2 losses are exponential, it is better to have as high a voltage possible with the lowest amperage. When these lines get to their destinations, they start breaking down thru transformers again to raise the amperage and lower the voltage. The transformers you see on poles reduce the 50,000 volts down to around 9,000 volts. Then as they spread thru to homes, voltage is again lowered to around 220 volts, what comes into the house for us to use. Actually we get 2 lines of 3 phase electricity of 110 volts each.
One interesting fact - how fast does electricity go thru your home wires from the fuse box to the outlets? Not the speed of light, which many people think. If it went that fast, the resistance in the wires would fry immeadiately. Actually it travels at about 10 meters per second. About the speed of a fast walk. People think the speed of light because when they turn on the light switch, the light comes on at the same time. Try to think of electricity in wires as the same as water in a hose. If the garden hose is full of water, when you turn it on, the sprinklers will come on at the same time. The 'water' in electric wires are the electrons of the copper. They are always full of electrons since wire is copper. When you turn the light switch on, the electricity being pushed thru the wire at the switch pushes the first electron, which pushes the next, which pushes the next, etc.