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post #1 of 10 (permalink) Old 09-19-2008, 04:27 AM Thread Starter
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Curious about electricity

Thanks to Ike, I recently got to spend a few days without power (not whining, just stating). Anyways, it got me thinking about electricity and how it works. I have a cursory knowledge of how electrical works, but was wondering if anybody on here could fill me in a bit more specifically.

Basically I'm curious about different stages the electricity goes through between the power station and the consumer. What's the purpose of substations? Transformers? The difference between Single-phase and three-phase? Is there 2-phase power?

Also, what is the difference between volts, watts, amps, etc?

Anybody with knowledge and experience feel free to chip in. I'm especially anxious to hear from vash on the subject, so if you got some free time and can chime in, I'd appreciate it. You don't have to go into extreme detail; you can simplify if you want and I'll ask for clarification if it's not sinking in.

"The only difference between death and taxes is that death doesn't get worse every time Congress meets."
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post #2 of 10 (permalink) Old 09-19-2008, 06:42 AM
 
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Ok, first thing first, if you haven't already, read the "loss of power" thread.

Alright, the golden rule of electricity is Current=Voltage/Resistance (I=V/R) known as ohm's law. Often, people use the water comparison. Current is how much water is flowing, voltage is how much pressure is forcing the water to flow, and resistance is how much constriction there is in the hose. Its pretty self evident from there. The more pressure, the more flow you get. The smaller the hose, the less flow.
Power transmitted, is a combination of current and voltage. Lots of current and voltage=lots of power. Little of both, little power. A lot of one but little of the other, medium power. It really doesn't matter which one is big and which is small, power is the same. Power is measure in watts, and the formula is watts=volts*amps
So to sum up.
Voltage, Volts, is the pressure that causes electrons to flow from one side to the other
Current, Amps, is the ammount of electrons that are flowing
Resistance, Ohms, is how much resistance to flow there is
Power, Watts, is the combination of voltage and current.

Ok, now, remember the whole speech about magentic lines crossing conductors causing current to flow thru conductors? (if not look it up) Well here is how a transformer works.
You have two coils (just conductors) sitting next to each other. As current builds up in one conductor, lines of magnetic force cross the other conductor and cause current to flow thru it. The conductors are not connected, but power gets transmitted. If you make the coils have a different quantity of loops (one with many and one with few) you can exchange current for voltage. The side with many coils will have lots of voltage, but little current. The side with few coils will lots of current, but little voltage. But the power will be the same on both sides (well, almost the same. Transformers loose some power because nothing is perfectly efficient).
Now, transformers only work with AC. The reason for this is that with DC, current flows on way. So lines of magnetic force build up as current starts flowing and then just stay there. But in order for current to start flowing in the other side of the transformer, lines of force actually have to cross the conductor. With AC, Current moves in one direction, then stops, then moves in the other, and repeats. So lines of magnetic force build up and collapse, build up and collapse. When they do this, the cross the other conductor over and over again.
Now, no wire is 100% efficient. It has some resistance. So some power is going to be spent, just traveling down the wire. But, if you have high voltage and low current, than very little power will get spent going down the wire. And if you have lots of current and low voltage, than lots of power is going to be spent. Power companies don't want to waste power on their lines, they want to sell it. So they transmit power under huge voltage (quarter of a million volts or more), and very low current. This limits the losses in the line, but high voltages are very dangerous, because they can cross high resistances (Like air, or people). So the close you get to the point of use (your house) the power company turns down the voltage and increases the current, via transformers. This increases the losses, but since the distance is small, the losses stay small. These transformers are located at switching stations. The other thing that switching stations do is control the way power flows. If there is greater need of power in one region, the reroute it from several power plants to go in that direction.
Three phase power is a little tricky. In a generator you have the whole spinning magnets and conductor coils thing. Well, there are three sets of conductors. So current builds in one as magnet passes it, but then starts to drop as the magnet pulls away, but the magnet also gets close to the next conductor coil, so power starts to built in it, and so on and so on. This is why they are called phases. If you look at a graph of current in each conductor, the peaks dont line up. They are off from each other, out of phase, phased over, whatever term you want to use.
If you need lots of power, it makes sense to use several phases. This basically splits the power up in between three wires, so that each wire carries less (and so the wire can be thinner and cheaper). But if you only need a little power, then you can just use one phase, and save yourself some money on wire. Most household stuff doesn't need a whole lot of power. So you use a single phase, just a single wire. The voltage in this wire goes up and down up and down, being AC and all. Then you have a second wire, called neutral, which is just a return path. If you touch the Hot wire it will shock you, but the neutral wire will not. The ground wire is just added in for safety, it doesn't actually do anything.
But, for high power, industrial applications, you use all three phases to transmit power, using three wires, all of which are hot. There is also a ground wire, again, for safety. If you take any of the hot wires, and a neutral wire from somewhere, you get single phase power.
And there is no dual phase, its just a term that is not used. Even if you use two phase wire to power something (which is done) its not called dual phase. I don't know why.

The reason ground wire makes things safer is this. If something breaks inside your all metal washing machine, and a hot wire comes loose, there is a good chance that it will touch the outside metal case. If the metal case is grounded, then it will short out, and blow the breaker, and you have to hire someone to fix it. However, if the outside case was not grounded, then the loose wire would just charge it, bring it to the same voltage as the wire. No breaker would trip, and when you touch the case you would be for quite a surprise, since you will be the path of the short.


Hope that helps



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post #3 of 10 (permalink) Old 09-19-2008, 07:25 AM Thread Starter
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I guess that pretty much sums it up. Question about grounds though: what happens to the electricity when it reaches the end of the ground wire? Does it literally just disperse? If so, how does this work on cars/boats/planes?

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post #4 of 10 (permalink) Old 09-19-2008, 07:37 AM
 
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No, its doesn't disperse, its uses the ground to travel back to the power plant.
In the case of boat/car/whatever, the ground is the chassis. Then electricity uses the chassis to travel back to the alternator.
There must be a complete path for current. It is not enough for it to get to the point of use, it also has to return.

Of course, with AC, electrons don't really return, since they keep on changing direction all the time, but you still have to have a path, so that the wave can go from one end to the other, if that makes any sense.



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post #5 of 10 (permalink) Old 09-19-2008, 12:49 PM
 
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im wonder if my relation could be called accurate.... Talking about Volts & Amps here in relation of horsepower & torque... kinda out of the box thinking but it sounds right to me...

Volts is to horsepower; as Amps is to torque


huh
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post #6 of 10 (permalink) Old 09-19-2008, 01:39 PM
 
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umm, no, its not accurate at all. sorry bud.

Torque is force, horsepower is power.

Torque is like being able to bench press 200lbs.
Horsepower is like being able to bench press 200 lbs 10 times in a minute.

With torque (force) all you specify is how much force you are putting out. With power you specify not only how much force, but also how often.



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post #7 of 10 (permalink) Old 09-19-2008, 01:50 PM
 
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well you can have tonns of horsepower and no torque and not move an inch, hypothetically ofcourse, and you can be shocked with millions of volts and still be ok.... but once you get that torque it gets moving; and once you get those amps, you die.


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post #8 of 10 (permalink) Old 09-19-2008, 02:12 PM
 
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Alright, I'm not even sure what you just said.

Here is where the HP/Torque misconception gets started. In a typical, unblown enigne there is a basic compromise. Have a long stroke, and the engine makes lots of torque, since the crank shaft has a bigger distance between the bearings. However, with a long stroke, the linear piston speed is high, and so the red line is pretty low. An engine like this will feel strong right of the bat, but will wind itself out quickly. On the other hand, if you make a short stroke/large bore engine the torque will be low, but red line will be high. With a high rpm, you can cram more power pulses into one minute so overall horsepower is high, even is peak torque is low.
So people started saying that engines with a strong low end are "torquey".
But that analogy only goes so far. a turboed engine will often have much higher torque than horsepower. But that torque doesn't kick in until the turbo spools up, at high rpm. So the engine can be gutless in the low end, and still have high torque.
Also, as the engine gets to spinning faster, all sorts of little tricks become available to the designer, allowing increased torque thru increased volumetric efficiency. That is to say, the air in the ports start flowing so fast, that even when piston reaches bottom dead center and starts to come back up, the air keeps on flowing into the cylinder, simply because it can't stop. So its kind of like blowing an engine without a blower.
What really matters in an engine is horsepower distribution, i.e. the whole graph. But there is no good way to brag about that stat, so people like to brag about peak horsepower, which isn't very meaningful. However, from the peak, one can at least guess what the horsepower curve might look like. People who brag about peak torque are complete retards, as this is the most useless stat to describe an engine. Say an engine has 600 foot-pounds of torque, is that good or bad? Well that depends. If its 600 ft-lbs at 10,000 rpm that engine is a monster. It is also most likely blown by a huge turbo and completely un drivable, due to the insane lag. If the 600ft-lbs comes at 3,000 rpm than you got yourself a pretty good muscle car that can embarrass people at stop lights (without having to learn how to work a manual tranny well) with a quick take off but will most likely get its ass handed to it by a real racer on a track. If 600 ft-lbs comes at 100rpm, than you are looking at a useless old single cylinder that couldn't get you to 15mph.



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post #9 of 10 (permalink) Old 09-19-2008, 02:17 PM Thread Starter
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If I had a ZR-1 I'd brag about the torque. This I know for sure.

"The only difference between death and taxes is that death doesn't get worse every time Congress meets."
-Will Rogers
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post #10 of 10 (permalink) Old 09-19-2008, 03:03 PM
 
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Quote:
Originally Posted by Vash View Post
Alright, I'm not even sure what you just said.

lol



a riddle...
wind is to flag; as swim is to fish

Last edited by ochoa0042; 09-19-2008 at 03:06 PM.
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