Wacky Weekend: NERC to relax power grid frequency strictures

Ingo Flaschberger if at xip.at
Sat Jun 25 22:47:07 UTC 2011

>> Generators all stay in sync.  Generator owners have expensive devices
>> that sync the phase before the generator is connected to the grid.  Once
>> a generator is connected to the gird, it will stay in sync - in fact
>> that is why they have the expensive devices to make sure that they are
>> in sync before they connect them, as if they are not, it will instantly
>> jump to being in sync, which may destroy the generator.
> As a matter of fact, it may destroy the generator, the housing, the building,
> the damn, and more. An out-of-sync generator becomes a motor until it is
> in sync. lt can be a graphic and dramatic event.

Big generator are synchron maschines, as they can generate also reactive 
power. If a out of sync synchron maschine is connected to the grid, theres 
a big "kawumm" and then the maschine is in sync or dead.
Only the angle between the rotor and the magentic field make the 
difference between generator and motor.
A synchron motor can not self-start and only run at fixed grid freuency / 
rpm's. A overloaded motor suddenly stops.

Smaller generators are asynchron maschines, that can run faster or slower 
than network frequency - ie run as generator or motor - but they always 
consume reactive power.
They can self-start.

Synchronising maschines to a grid is not a big problem, the bigger problem 
is to syncronise 2 disconnected grids.
Some years ago in europe a grid operator violated the n+1 redundancy rule 
as he needed to switch of a big power line over the river "Ems" - to 
allow a big ship to leave the shipyard.
The result was a netsplit trough whole europe - a lot of "big" 
line-breakers flipped and switched of north-west and south-east power 
The whole european grid was split into 3 parts, running at higher and 
lowet frequencies.


Kind regards,
 	Ingo Flaschberger

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