[time-nuts] Line Frequency standard change - Possible ?
kb8tq at n1k.org
Thu Feb 9 17:59:14 EST 2017
> On Feb 9, 2017, at 4:31 PM, Poul-Henning Kamp <phk at phk.freebsd.dk> wrote:
> In message <4FBDD81DDF04FC46870DB1B9A747269202916B42 at 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.
> In the traditional AC grid power is produced by big heavy lumps of
> rotating iron. This couples the grid frequency tightly to the
> power-balance of the grid: If the load increases, the generators
> magnetic field drags harder slowing the rotor, lowering the frequency
> and vice versa.
> This makes the grid frequency a "proxy signal" for the power balance,
> and very usefully so, because it travels well and noiselessly through
> the entire AC grid.
> The only other possible "balance signal" is the voltage, and it
> suffers from a host of noise mechanisms, from bad contacts and
> lightning strikes to temperature, but worst of all, it takes double
> hit when you start big induction motors, thus oversignalling the
> power deficit.
> Where the frequency as "proxy" for grid balance reacts and can
> be used to steering on a 100msec timescale, you need to average
> a voltage "proxy" signal for upwards of 20 seconds to get the
> noise down to level where you don't introduce instability.
> The big picture problem is that we are rapidly retiring the rotating
> iron, replacing it with switch-mode converters which do not "couple"
> the frequency to power balance.
> For instance HVDC/AC converters, solar panel farms, and increasingly
> wind generators, do not try to drag down the frequency when they
> cannot produce more or drag the frequency up when they can produce
> more power, they just faithfully track whatever frequency all the
> rotating lumps of iron have agreed on.
> As more and more rotating iron gets retired, the grid frequency
> eventually becomes useless as a "proxy-signal" for grid balance.
> Informal and usually undocumented experiments have already shown
> that areas of grids which previously were able to run in "island"
> mode, are no longer able to do so, due to shortage of rotating iron.
> One way we have found to make the voltage a usable fast-reacting
> proxy for grid power-balance, is to lock the frequency to GNSS at
> 1e-5 s level at all major producers, which is trivial for all the
> switch-mode kit, and incredibly hard and energy-inefficient for the
> rotating iron producers.
> The other way is to cut the big grids into smaller grids with HVDC
> connections to decouple the frequencies, which allows us to relax
> the frequency tolerance for each of these subgrids substantially.
> 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?
> (It is already bad enough with cable capacitance in long HVDC
> connections, do the math on 15nF/Km and 100.000 kV yourself.)
> All these issues are compounded by the fact that the "50/60Hz or
> bust" mentality has been tatooed on the nose of five generations
> of HV engineers,
Umm… you left out the 25Hz power system that runs across the
road just a few miles from here :) Some of these ideas take a *long* time
to die. It’s been happily doing it’s thing for over a century.
> to such an extent that many of them are totally
> incapable of even imagining anything else, and they all just "know"
> that DC is "impossible”.
Except we’ve had HVDC distribution running around for many decades
and it seems to work quite well. Indeed that’s your point here.
> In the long term, HVDC is going to take over, because it beats HVAC
> big time on long connections, and it is only a matter of getting
> semiconductors into shape before that happens. That however,
> is by no means a trivial task: It's all about silicon purity.
… or silicon carbide purity or something even more weird and (so far)
> Poul-Henning Kamp | UNIX since Zilog Zeus 3.20
> phk at FreeBSD.ORG | TCP/IP since RFC 956
> FreeBSD committer | BSD since 4.3-tahoe
> Never attribute to malice what can adequately be explained by incompetence.
> time-nuts mailing list -- time-nuts at febo.com
> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the instructions there.
More information about the time-nuts