Originally Posted by
nomorecatering
It seems that wind turbines output frequency varies according to the rpm. How do they get a stable 50 Hz output with a constantly varying rpm? Some sort of frequency converter?
Like lots of this discussion Ozbusdrivers explanation is sort of, a bit right. There are actually a few different types of wind turbine configurations (search on types 1, 2, 3 etc) I dont know a lot about them as I only do work marginally related to any types of power generation these days. However, my understanding is that the earlier (?) types 1 and 2 were basically AC generators driven more or less straight from the blades (pitch control or blade shape controlling energy transfer from the blades to the alternator. Type 2 uses a wound rotor so can also have some electrical control. Later types 3, 4 (and 5?) do use various sorts of AC/DC conversion sort of like how Ozbusdriver describes. All the turbines types individually produce AC outputs (not DC) which is usually fed to a common AC bus for the farm as a whole. This bus is what is connected to the grid and to the grid the whole collection of turbines appears as one generator.
You will see comments that wind farms can't provide support to the grid (ie frequency and voltage support). This is certainly true of type 1 and 2, but the other types can (I think type 4 can actually be used as a stand alone generator, without being part of a wind farm bus).
I believe SA farms are mostly type 2 with some type 3. I would expect that future wind farms will only be allowed if they are the higher type numbers.
Which will then make some peoples heads explode as it seems one possible solution to make the SA system "more secure" is to build ... more wind farms!
(Of a suitable type, see, nothing is simple)
Originally Posted by
nomorecatering
Why do power stations require an input voltage to start generating power.
My simple explanation. There are two reasons. One being to run auxiliary plant, the second being to synchronise the generator to the "system". Mostlytossas posts are a good basic analogy for starters. He and I might quibble about better ones, but they are good to start with (I did work in a power station for a good few years).
Originally Posted by
nomorecatering
Why do power stations take so long to spool up, if they had steam pressure, wouldn't the generators spool up quite quickly? Do they reduce the steam generation in periods of low demand.
In simple terms it takes a long time to heat up a lot of water to make steam. A big boiler with big output will take longer. There may also be limits of rate of heating of eg. turbines if they are not up to operating temperatures. From dead cold, some power stations may take _days_ to get to full load.
Yes, steam generation is reduced at times of lower load. As a basic relationship, power out exactly equals steam in and power out is exactly needed to match the load on the system.
Originally Posted by
nomorecatering
During periods of increasing demand from consumers, does this extra load cause the generator rpm to decay, reducing the frequency, if so why would damage occur if the frequency output of the generators falls below 47 Hz.
How does the system cope with instant demand increases when hundreds of thousands of people put the kettle on at the same time during a commercial break on a popular TV show. I think they call it the East-Enders effect. A TV show in the UK that was massively popular and they could predict the spikes in electricity demand from the Ad breaks.
If the boiler and turbine is up to temperature and operating at some level, yes, it is possible to dynamically extract a bit more steam out (like a big compressor receiver) to generate a bit more power in the very short term. This is how the Eastenders problem is overcome (and everyones kettles on all at once is still quite small compared to the overall system). Problem is, if you drop the pressure too much, wet steam can get into the turbine blading, which will destroy them in short order and the multi ton alternator with rotor spinning at 3000 RPM will leave the floor shortly after that.
The 47Hz thing is not the problem as such (although there are problems because of it) Rather it is an indicator that other bad things are about to happen(like alternators leaving the floor). In a normally functioning system the turbines wont (cant) slow down as they cant change speeds due to being synchronised. If they have, then something is bad wrong with the whole system.
Note that .
As an aside the NEM pays power stations to be able to quickly pick up this transient load. These are some of the ancillary services that generators can bid and contract for in the electrical market (like the SRAS mentioned by gerry111 earlier). It isn't just about MegaWatts. The boiler of the power station in Port Augusta is (was?) a "once through" design (Benson boiler) so actually was worse than normal for being able to cope with rapid load changes consequently they couldn't provide this support and so couldn't get money in this part of the market.
Originally Posted by
nomorecatering
Lastly, why do we have backup services that are secret (provider 1 and provider 2). This, to my simple mind is unacceptable.
I know who they are. Electricity industry participants would probably be able to easily find out who they are if they dont know already. I suspect it is a "commercial in confidence" contractual thing.
Originally Posted by
nomorecatering
I hope the questions don't sound too dumb...
No (good faith) questions are dumb. Some answers may be.
Certifs