On 2/9/17 1:31 PM, Poul-Henning Kamp wrote:
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In message <4fbdd81ddf04fc46870db1b9a747269202916...@mbx032-e1-va-8.exch032.ser
verpod.net>, "Thomas D. Erb" writes:
I was wondering if anyone was familiar with this proposal, is this
a uncoupling of line frequency from a time standard ?
The interesting thing about this is that all research and experiments
(for instance on the danish island Bornholm) indicates that the only
way we stand any chance of keeping future AC grids under control in the
medium term is to lock the frequency *hard* to UTC.
Its a very interesting topic.
<snip of interesting discussion>
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.
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)
The Pacific Intertie is 1MV at 3000A for 1360 km.
2 bundled conductors 10m apart is about 10pF/m, or 10nF/km (vague
recollection from somewhere)
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.
In comparison, the fairly large Marx at the Deutsches Museum is 33 nF at
1.2 MV..
(It is already bad enough with cable capacitance in long HVDC
connections, do the math on 15nF/Km and 100.000 kV yourself.)
underground cables have substantially higher capacitance.. I think your
number is a "suspended in air" value.
I'm not sure that's as big a deal.. the stored energy in cables (as
opposed to overhead lines) is also a big problem with AC distribution..
transient settling times are enormous and it leads to big stability
issues. Pretty much, you can use long AC cables only for unidirectional
power transfer "source to load" not for "source interconnect" because of
the stability problems (with that rotating iron)
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