[time-nuts] Line Frequency standard change - Possible ?

[Poul-Henning Kamp]

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In message <63beea7a-f9fc-6e1d-b855-2c7056de3cc7 at earthlink.net>, jimlux writes:

>I think also of the issues from distributed generation - consider a 
>rooftop solar installation with 20 or so MicroInverters, all "slaved" to 
>the line.  Just from manufacturing variations, I suspect each 
>microinverter is a little bit different than the others.

Surprising there is almost no variation, because it hurts badly on
both your nameplate efficiency and thermal design.

>> This solution gets even better if you load the HVDC up with capacitance
>> to act as a short time buffers, but the consequences in terms of
>> short circuit energy are ... spectacular?
>
>yeah, but that's a "solvable" problem in terms of circuit breaker 
>design. We've all seen the Lugo substation video (not DC, but big AC 
>with the suppression disabled so it can "pull an arc" for test)

Yes, that's the easy case, and good old dynamite based emergency
switches work too.

But shorts are another matter:  They are so much easier to deal
with when you have regular zero-crossings a hundred times a second:
HVDC shorts are explosions which doesn't end until you've used up
all the energy.

>The pacific dc intertie is a lot more than 10m apart, so it's probably 
>lower, but still..  14 uF @ 1MV is a bunch o'Joules. (about 14 Mj) 
>Fortunately, there's a fairly large series L also to slow down the 
>transient.

Yes, it slows down the front flank, on the other hand, once you get
the arc going, with DC that L really keeps it going for a long time.

The difference in practice is that a HVAC short leaves a burn-mark
on the metal parts, HVDC solidly welds them together if it doesn't
outright melt them.

-- 
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