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.
Pete.
On 2/9/2017 6:55 PM, Poul-Henning Kamp 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 <p...@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.
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.
So far no such regulation has been enacted, but everybody expects
it to happen after the next big urban blackout.
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