Hi > On Feb 9, 2017, at 6:55 PM, Poul-Henning Kamp <[email protected]> wrote: > > -------- > In message > <CANX10hC=ayCN_hs8EdPCt0tK=szmrs51pm2jxj+aj_o5w39...@mail.gmail.com> > , "Dr. David Kirkby (Kirkby Microwave Ltd)" writes: >> On 9 February 2017 at 21:31, Poul-Henning Kamp <[email protected]> wrote: >> >>> >>> 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. >>> >> Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 >> >> I'm not sure what you mean by "balance signal" here. > > By "balance signal" I mean "which meter tells you if you need more > or less power in the grid". > >> He said that he would >> receive a call from the CEGB, saying they wanted X Watts, and a power >> factor of Y. > > Exactly. > > Back when it was all rotating iron, they would only have > asked for the "X Watts" and they would do so because the frequency > was sagging, because that was the "balance signal" telling them > that more power was getting used than produced (or vice versa). > > These days it has gotten much tricker, and I think getting into > all the details may be stretching the patience here on time-nuts, > but let me just give you two examples of how the consumption side > has also made the job harder: > > It used to be that pretty much anything which drew power from the > grid would be (give and take at bit of powerfactor) an ohmic loads. > > That means that if you sag the voltage, consumption drops (motors > run slower, lamps are dimmer etc, and vice versa, high voltage would > make consumption increase. This was a beneficial feedback mechanism > trying to keep the grid stable. > > These days almost anything, including computers, cars, washing > machines and lightbulbs, have a switch-mode PSU which makes it a > constant-power load. > > This means that if the grid voltage increases, current drops, > reducing transport losses, which increases the voltage further. > And vice versa. This can make voltage regulation *much* harder. > > The other factor is batteries. (This was first noticed during the > rolling blackouts in California caused by Enrons market manipulations.) > > A city block would drop out at X kW, and usually when you cut it > in again it would be Y% higher because all fridges and aircons would > want to start. > > Thesedays when you cut in a cityblock it comes in at the same > +Y%, and then about five seconds later all the chargers, > in UPS, laptops, mobile phones and whats not, cuts in, and > that can more than double the Y% and in some cases takes > the grid right back out. > > Regulations have been proposed that it would make it illegal to > change *any* battery if the frequency is below some set limit, > in order to ensure that the grid can be relit faster and with > less energy.
One simplistic way to look at all this is that a switcher presents a “negative resistance” load. If you drop voltage, current goes up. OCXO’s happen to share this issue. Negative resistances are *not* what most power source guys want in their control loop. Bob > > So far no such regulation has been enacted, but everybody expects > it to happen after the next big urban blackout. > > > -- > Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 > [email protected] | 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 -- [email protected] > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
