Hi 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.
Bob > On Feb 9, 2017, at 5:19 PM, Peter Reilley <preilley_...@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 > system. > > Pete. > > On 2/9/2017 4:31 PM, Poul-Henning Kamp wrote: >> -------- >> 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. >> >> 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. >> >> > > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
