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

Peter Reilley preilley_454 at comcast.net
Thu Feb 9 17:19:49 EST 2017


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
system.

Pete.

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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