[time-nuts] Line Frequency standard change - Possible ?
kb8tq at n1k.org
Thu Feb 9 18:54:54 EST 2017
If you are talking about big power gizmos, putting a GPSDO on them is pretty simple
cost and system wise. Given the fact that 10 ns sync is not required, the actual implementation
might be pretty cheap.
> On Feb 9, 2017, at 5:19 PM, Peter Reilley <preilley_454 at comcast.net> wrote:
> Isn't this "hard" lock to UTC creating a single point of failure? A solar burst, an EMP, or
> a software error could leave us all in the dark. After all, smart inverters could be
> programmed to act like big lumps of rotating iron and be compatible with the current
> On 2/9/2017 4:31 PM, Poul-Henning Kamp 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, 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".
>> 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.
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