[clug] Exercise and pay the bills!

[jm]

Robert Edwards wrote:
>
> btw. does anyone know how the electricity authorities "switch off"
> a segment of their 240V power line (eg. for tree-clearing or other
> maintenance) when there are all these solar-powered power feed-ins
> popping up everywhere and effectively juicing up the line? I have
> always wanted to know how they turn it all off.
>
>

I've wondered this myself. At a guess, I'd say it's part of the 
circuitry that does the phase advance. If there isn't a voltage on the 
level above some threshold the inverter wont operate. If there is a then 
it attemps to lead the phase be a certain amount inorder to feed power 
onto the grid.

http://ece-www.colorado.edu/~ecen4517/materials/refs/inverters/BlaajbergInverters2005.pdf 
say,

The inverters must also be able to detect an islanding situ-
ation, and take appropriate measures in order to protect per-
sons and equipment [7]. Islanding is the continued operation
of the inverter when the grid has been removed on purpose, by
accident, or by damage. In other words, the grid has been re-
moved from the inverter, which then only supplies local loads.
The available detection schemes are normally divided into two
groups: active and passive. The passive methods do not have any
influence on the power quality, since they just monitor grid pa-
rameters. The active schemes introduce a disturbance into the
grid and monitor the effect. This may affect the power quality,
and problems with multiple inverters in parallel with the grid
are also known to exist [7], [8].

It goes into more detail, which I haven't had a chance to read having 
just found this document, put includes schmatics of various configurations.


Jeff.