I know that nuclear energy heats water, and the water turns turbines.
What I don’t understand is how steam turning machinery produces electricity.
Also, why can heat not be turned directly to electricity, as opposed to the (seemingly) roundabout way of heating steam, and making things move?
Come to think of it, how does electricity make things move (toy cars etc)?
I suppose what I’m asking is how we turn one type of energy into another, such as
heat > kinetic > electricity, and then electricity > kinetic? or electricity > heat?
why not heat > electricity?
I never took physics, so my knowledge of this area is non-existant.
Given the membership of the SDMB maybe somebody will take a real crack at this but you are really asking for a full explanation of electricity, generators and motors - not something to do in a single post!
The missing link you need is magnetism. If you move a wire through a magnetic field you will induce a current to flow in the wire. Steam turns a rotor which turns inside a magnetic field and causes charge to move along the wires. It’s more complex than that of course but that’s the basics of it.
For the second part of your question, there are a lot more possibilities. Electricity can be used in a variety of ways to produce motion but the most common way is just the reverse of generation. Applying electricity to the conductor can make it produce a magnetic field around it which interacts with another magnetic field to produce motion. You could use magnets to create one field, then apply current to the wire to create the other field and they will repel or attract (depending on the design of the motor) to move the shaft.
It can. By use of something called a thermopile. In deep space probes, thermal heat from plutonium is used to keep one side of a thermopile hot, while the other side remains cool. The thermopile converts the temperature difference directly into electricity. It’s not very efficient, so it’s only used in special appplications.
Keep in mind, though, that regular 'ol heat (alone) won’t work. You need a temperature difference.
While motors are common and efficient, I suppose it should be mentioned that there are other ways electricity can “move” things. A couple that come to mind:
There actually is a way to produce electricity directly from heat (or at least from a temperature difference) - it’s called a thermogenerator, but they are much. much less efficient than the seemingly cumbersome heat->steam->spinning coils->electricity system that most power plants use. There are other direct-conversion systems, including “Thermionic converters” and PhotoVoltaic cells, but these aren’t particularly efficient, either.
Thermogenerators are being explored to harvest some of the waste energy from automobile engines.
Whether you can turn heat directly into electrical power is an interesting and subtle question. If you have a source of heat at a higher temperature, and something you can dump heat into at a lower temperature, then you can convert some of the heat into electricity while you let the rest of the heat flow into the dump. If the heat source has an absolute temperature that is X times as high as the dump, and you had some kind of converter that was perfectly efficient in a certain sense, you can convert (X-1)/X of the heat into electricity. If I got that right, anyway. This is the point of entropy and the Carnot cycle and, in a more distant way, the second law of thermodynamics and randomness.
An early view of this held that heat energy falling through different temperatures was like water falling through different altitudes, in that what you put in at the top would come out at the bottom and it could do work along the way. But it turned out not quite correct, because you don’t get all the heat out at the bottom, unlike the water situation. Some of the heat is what got converted into electrical power.
Crafter Man is right to point out thermopiles, and they take advantage of an interesting effect, the Kelvin effect. Heat energy is in the form of vibrations over a wide range of frequencies including the very high, over small distances. For example, in our world of about 300 K (room temperature) to 3000 K (incandescent light bulb filaments), the frequencies are in the microwave and visible light parts of the electromagnetic spectrum, and their amplitudes are a few percent of intraatomic and intramolecular distances (which we consider melting or breaking down when they are exceeded). All these vibrations shoot randomly around in an object of uniform temperature, but if there is a thermal gradient, and heat energy is flowing, the waves are moving more in the downhill direction than the uphill direction, and they tend to wash electrons along with them. It’s like seaweed washing up on the beach. This is the basis of thermopiles and thermocouples. You make a complete circuit that contains two different materials that have different strengths of the washing effect, with the same gradient on both materials.
Very approximately, we produce electricity by spinning a magnet inside a coil of wire.
The principle is called “induction” because a moving magnetic field “induces” electric current to flow in the wire.
In power stations, various sources of power are harnessed to turn the generator shaft. If you are curious about how we generate electricity in Ireland or in any specific power station, I can give you as much detail as you want (and more!)
The frequency of a generator is determined by how many coils of wire it has and how fast it is spinning. If you have one generator, you increase the frequency by giving it more steam (or more of whatever is driving it) and to decrease the frequency you give it less steam.
That only works for one generator though.
When you have a lot of generators, they tend to act almost like an infinite bus. You can’t change the frequency even if you want to. If you take your one generator and try to make it spin faster, all it does is supplies more power to the grid. It doesn’t actually run faster, it just gets harder to turn. Try to make it run slower and it supplies less power, until it becomes a motor, drawing energy from the grid. But it still doesn’t slow down. [for those who like to pick minor nits - it will speed up or slow down slightly, but not much]
Adjusting the frequency is therefore kinda tricky, because you have to adjust all of the generators at the same time. Minor adjustments aren’t too hard to make, though, and in the US the frequency is adjusted periodically so that in the long term it is exactly 60 Hz on average. If you run a clock with a synchronous motor from AC (which used to be common, but is now almost unheard of), the clock may be a little fast or slow at certain times during the day, but you will never ever need to adjust the clock. In the long term it will always be correct.
Bringing a generator online is kinda tricky. You can’t just throw the switch at any old time you feel like it, or your huge rotating machine will become a huge pile of scrap metal. What you do is get the frequency “close enough”, then use something like a synchroscope (a special meter that shows you the phase difference) or synchronizing lights to get the generator exactly in phase with the line. When it is close in frequency and exactly in phase, then you throw the switch, and the generator then just naturally becomes locked to the line frequency.
I was about to nit pick but I saw that you had answered it.
I heard of a case where the man on the disconnect got excited and pulled in when the lights were the brightest. Blew every fuse and breaker between Fan Francisco and where the ship was tied up in Vallejo.
If you are awake it is really easy, but you want to be quick. When the plant has only two or three generators you have to spllit the load by incrreasing one govenor as you decrease the other.
ecg has answered this question very well - not sure I can add much.
As he says, the frequency is determined by the speed of the turbine, and there is a control system in place to admit more steam if the speed is dropping, and less if the speed is increasing. In Ireland the system frequency is 50 Hz, which corresponds to a turbine shaft speed of 3000 rpm (assuming a 2-pole generator). In the USA it’s 60/3600.
If the generator is one of many feeding into the transmission system, they will all be synchronised and “forced” to run at the same frequency. If you want to connect a generator to the system, it has to be spinning not only at the right frequency but also in phase with the system, or there will be a hell of a bang.
In reality the system is not infinite. If we have 4000 MW connected in an island system, and suddenly a 400 MW unit trips, this will result in a dangerous drop in system frequency. The frequency might drop, for example, from 50 Hz to 49.2 Hz. This is dangerous because it could result in other generating units also tripping, in a runaway effect that could theoretically black out the whole country (it’s never happened).
So if the speed of the generators is determined by the system frequency, what determines the system frequency? Well, some of the generating units are set up to provide frequency response - rather than trying to maintain constant voltage and power output, they react to a drop in frequency by increasing their output. This is a service provided by the generators to the transmission system operator. Quick response (on the order of milliseconds) is vital - it’s much easier to rescue a situation when it’s just starting to drop.
