[time-nuts] Line Frequency standard change - Possible ?
preilley_454 at comcast.net
Thu Feb 9 22:59:18 EST 2017
Even in the old days a lot of devices were constant load, independent of
voltage (within reason).
Anything regulated such as electric heat, electric hot water, and
refrigerators are constant load.
Synchronous motors (most motors) are frequency dependent. They do get
less efficient at lower
voltages because their slip speed increases but that is a small percent
of their running speed.
Non-synchronous motors are often speed regulated so they are constant
load. Electric transportation
is constant load.
I am sure that I could come up with more examples.
Utilities found that dropping the voltage was not very effective at
shedding load in emergency
situations. However, rolling blackouts do work very well.
On 2/9/2017 6:55 PM, Poul-Henning Kamp wrote:
> In message <CANX10hC=ayCN_hs8EdPCt0tK=SZmRS51pm2JXj+Aj_o5W390Eg at mail.gmail.com>
> , "Dr. David Kirkby (Kirkby Microwave Ltd)" writes:
>> On 9 February 2017 at 21:31, Poul-Henning Kamp <phk at phk.freebsd.dk> 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.
> 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.
> So far no such regulation has been enacted, but everybody expects
> it to happen after the next big urban blackout.
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