>> know that the system uses not PV cells but heated oil which in turn
>> produces water-steam to drive turbines to make electricity.

>There's a large wind-turbine "farm" going up on the Gippsland coast 
>here in
Victoria. The wind doesn't blow all the time (duh!) and when it does 
the
turbine blades (3-bladed model in this case) can rotate at any speed 
from dead
slow to damn fast. The power grid they contribute to is 3-phase, 415V, 
50Hz in
Australia. So how to they synchronise the turbines' output to the 
required
frequency and phase? Just curious.
/>


Imagine a very large number of people are pulling a fully loaded 
Kenworth "Road Train" (you have to be in Oz!) at 5 kph. A long and 
strong and not tooo flexible tow rope stretches out ahead and several 
thousand people are pulling on it.

You decide to join in. At first you only give it 10% effort. Many 
people are putting in more effort than you are. How fast do you pull 
compared to everyone else? You slowly ramp up your effort until you 
are contributing 10 times as much input as when you started - right up 
to 100% of your capability. You are now putting in more effort than 
most individuals. How fast are you pulling compared to everyone else? 
What is the spread of pulling speeds of the individuals involved (as 
opposed to their power inputs)?

While the model above is not perfect it gives a fair feel for putting 
energy into an infinite bus. If the system impedance is very low and 
your power input is small compared to the total then you have the bull 
by the tail and he largely dictates what you do.

In AC systems power providers can change phase angle relative to 
system frequency and this will alter their power input. Push too far 
and you suddenly "slip" over the power peak and skate down the other 
side. Must do wonders for local users.

When DC links are used to transfer power, as often happens with very 
large underwater cables, the receiving end equipment must reconvert 
the DC to AC and then sync it to the mains it is providing power to. 
As long as the driven bus is "stiff" all is well. Typically AFAIR rule 
of thumb says the DC link shouldn't contribute more than 10% of the 
total power for reasonable prospects of stability. An example was the 
Island of Sardinia where they tried to provide a far larger percentage 
via DC link. Here the tail tended to wag the dog with massive 
instability problems.

NZ has a substantial DC link between the North and South Islands. 
AFAIK they run the cables at + and - 350 kV and total capacity is 
somewhat over a Giga Watt.


The NZ cable story.
Rather long. More likely to interest NZers who saw it all happen or 
irredeemable power engineers.

        http://www.techhistory.co.nz/Electricity/Cookstcable.htm



        Russell



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