Line Frequency standard change - Possible ?
Hi
On Feb 9, 2017, at 6:55 PM, Poul-Henning Kamp phk@phk.freebsd.dk wrote:
In message CANX10hC=ayCN_hs8EdPCt0tK=SZmRS51pm2JXj+Aj_o5W390Eg@mail.gmail.com
, "Dr. David Kirkby (Kirkby Microwave Ltd)" writes:
On 9 February 2017 at 21:31, Poul-Henning Kamp phk@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.
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
phk@FreeBSD.ORG | 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 -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
In message 28842754-1752-40E8-B3D5-F486A5DA9E26@n1k.org, Bob Camp writes:
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”.
Except we’ve had HVDC distribution running around for many decades
and it seems to work quite well. Indeed that’s your point here.
But if you look at the organization and regulation systems, the
HVDC end stations are not treated as transmission but as power
plants.
… or silicon carbide purity or something even more weird and (so far)
poorly understood.
The SiC hypers overlooked the C14 isotope beta-decay ionization
problem, and the anti-proliferation clampdown on ALIS have taken
away any hope producing C14 depleted raw materials. And even if
you did that, cosmic radiation would bring back enough C14 to be
trouble over the lifetime of the devices.
According to people in the HVDC electronics (if you can call it that)
business, we can build any of the devices we need from current
high purity semiconductors, but the costs need to come down.
--
Poul-Henning Kamp | UNIX since Zilog Zeus 3.20
phk@FreeBSD.ORG | TCP/IP since RFC 956
FreeBSD committer | BSD since 4.3-tahoe
Never attribute to malice what can adequately be explained by incompetence.
On 2/9/17 4:03 PM, Poul-Henning Kamp wrote:
In message 63beea7a-f9fc-6e1d-b855-2c7056de3cc7@earthlink.net, jimlux writes:
I think also of the issues from distributed generation - consider a
rooftop solar installation with 20 or so MicroInverters, all "slaved" to
the line. Just from manufacturing variations, I suspect each
microinverter is a little bit different than the others.
Surprising there is almost no variation, because it hurts badly on
both your nameplate efficiency and thermal design.
I was thinking about phase stability and "matching" to the grid.. each
microinverter (in a short time sense) might have a different phase
relationship (which turns into power factor), essentially introducing
some "noise" into the system.
But shorts are another matter: They are so much easier to deal
with when you have regular zero-crossings a hundred times a second:
HVDC shorts are explosions which doesn't end until you've used up
all the energy.
HV AC lines have exactly the same problem, the switches carry enough
energy that "quenching" the arc is by no means assured through the zero
crossing. If nothing else, inductance in the system (e.g. transmission
lines) insures that the voltage zero isn't at the same time as the
current zero.
There was a fascinating article about this in Scientific American back
in the 70s (Jan 1971, there was a picture of an airblast circuit breaker
on the cover). There's also a good description in IEEE Proceedings in
the article on Vacuum switching
http://ieeexplore.ieee.org/document/1451144/
Aug 73
The pacific dc intertie is a lot more than 10m apart, so it's probably
lower, but still.. 14 uF @ 1MV is a bunch o'Joules. (about 14 Mj)
Fortunately, there's a fairly large series L also to slow down the
transient.
Yes, it slows down the front flank, on the other hand, once you get
the arc going, with DC that L really keeps it going for a long time.
But 14 MJ isn't all that much energy in practical terms.. about a half
liter of gasoline (most fuels are around 50MJ/kg), or 3kg of high explosive.
yeah, 3kg of HE does a fair amount of damage, but it is localized (in a
10s of meters sense).
When the distribution transformer near my house blew up, I suspect that
a lot more energy was dissipated.. it was a 100kVA unit in a underground
vault, and it blew the 2x2m concrete vault lid 10s of meters away.
In reality, there's probably more stored energy in the L of the
transmission line than in the C. A quick back of hte envelope: 1
uH/meter is 1mH/km, so we're looking at 3000A in 1.3H. Oh, that's just
about the same as the energy in the C. about 12 MJ.
The difference in practice is that a HVAC short leaves a burn-mark
on the metal parts, HVDC solidly welds them together if it doesn't
outright melt them.
For big lines, the melting is "explosive" and doesn't leave much solid
metal behind.
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_o5W390Eg@mail.gmail.com
, "Dr. David Kirkby (Kirkby Microwave Ltd)" writes:
On 9 February 2017 at 21:31, Poul-Henning Kamp phk@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.
In message 043966d4-def4-4bc4-ba9d-ec46070fd33c@comcast.net, Peter Reilley wr
ites:
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.
Constant over the long term (hours), but not in the short term (seconds)
where grid stability is most important.
Utilities found that dropping the voltage was not very effective at
shedding load in emergency
situations.
No, it's no use for shedding load, but keeping things nice and
stable is much easier with a load which converges on your
target parameters, than with a load which diverges from it.
--
Poul-Henning Kamp | UNIX since Zilog Zeus 3.20
phk@FreeBSD.ORG | TCP/IP since RFC 956
FreeBSD committer | BSD since 4.3-tahoe
Never attribute to malice what can adequately be explained by incompetence.
On Thu, 09 Feb 2017 23:39:24 +0000, you wrote:
It is harder than it sounds.
Small solar inverters are the best, they an regulate down at milliseconds
notice, and many jurisdictions impose asymetric frequency bands on
them to exploit this.
Big inverters, no matter what you put behind them, get quite a bit
more expensive if they are designed to provide "non-VA" power,
because you suddenly have to run the current both ways in the same
half-cycle.
Nobody wants to pay for that voluntarily, and nobody are particular
keen to cause the first explosion/fire while they get the control-law
debugged.
Imagine how they will scream if they have to pay for fields of big
synchronous motors to be connected.
On Thu, 9 Feb 2017 19:06:51 -0500, you wrote:
One simplistic way to look at all this is that a switcher presents a negative
resistance load. If you drop voltage, current goes up. OCXOs happen
to share this issue. Negative resistances are not what most power source
guys want in their control loop.
Bob
People working with emitter/source followers do not like it either and
I cannot see the folks using inverters wanting to pay to put big
resistive heaters across the grid to compensate.
Adding power factor correction to switching power supplies was cheap
compared adding "negative resistance" correction.
On Thu, 9 Feb 2017 17:19:49 -0500, you 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.
I have the same concern. I am dubious of tying power grid reliability
to GPS reliability and doubly so in a threat environment which
includes hostile actors. And if an alternative more reliable timing
standard was used then why use GPS at all?
Inverters lack the overload capability and resistance of rotating iron
unless they are overbuilt in which case they would be uneconomical.
Work is already underway to improve the relicense of power grid
operations. They is smarting up quickly. The PMU/synchrophasor
measurements depend on UTC and before it can be used full-blown for
operation the single point of failure needs to be handled.
Cheers,
Magnus
On 02/09/2017 11:19 PM, Peter Reilley 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
<4FBDD81DDF04FC46870DB1B9A747269202916B42@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.
Hi Jim,
On 02/09/2017 11:39 PM, jimlux wrote:
On 2/9/17 1:31 PM, Poul-Henning Kamp wrote:
In message
<4FBDD81DDF04FC46870DB1B9A747269202916B42@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.
I think also of the issues from distributed generation - consider a
rooftop solar installation with 20 or so MicroInverters, all "slaved" to
the line. Just from manufacturing variations, I suspect each
microinverter is a little bit different than the others.
By code these needs to feed in phase with the line, meaning they do not
contribute with reactance as if it was rotating iron.
While trying to be "safe" is does not contribute to stability, only to
power.
Cheers,
Magnus