OT: solar superfalres

Long shot idea: our Sun is somewhat older than we think it is and the "Sun-like" stars they're looking at are actually somewhat younger, more energetic stars. Dating the Sun AFAIK is an indirect process it's assumed that everything including meteorites formed approximately the same time from the same accretion disk.

Maybe the Solar System formed from a merger of two large brown-dwarf systems whose "suns" had already been burning through heavier elements for a while but only ignited hydrogen fusion after they merged.

Well she don't look a day over 4.5 billion I don't think but she's actually 5.9

Brow-dwarf merger is probably much rarer than an older Sun that formed normally but mostly alone ripping off a younger nearby neighbor, though.

There was a fairly good review of our preparedness for another Carrington event or similar.

Nice description of what Carrington saw and its auroral effects:

We would get some advanced warning before the charged particles hit our magnetosphere so much sensitive gear could be switched off and/or put into metal boxes to protect it. Mains power lines in North America would almost certainly bear the brunt of the unavoidable damage. Magnetic north pole vulnerability is over on that side of the planet.

It has to happen *and* be headed in our direction before it causes any serious trouble - plenty of CME's occur and miss us completely. You know it is a good one if there are auroral displays visible from the UK (happens once or twice a year at solar maximum).

Right now the sun is very quiet and the only faint sunspot was even smaller than the tiny dot of Mercury in transit a week last Monday and the only flare on the limb just marginally bigger.

It is highly unlikely that the sun didn't form at the same time as the rest of the solar system. Its physics has been very well studied.

For two brown dwarfs to merge they would have to eject a third one or by pure chance score a direct inelastic collision inside the Roche limit. That is incredibly unlikley except in globular clusters where the star density is very high and the cluster becomes very more compact by expelling stars during three body collisions.

To qualify as a star it has to ignite hydrogen fusion with a core temperature of >10^7 before it runs out of the initial seedcorn fusion isotopes. Deuterium and hydrogen ignites first at about 10^6K. Then it burns progressively through Lithium, Beryllium and Boron until it either ignites hydrogen fusion in the core of fizzles out.

Flares are more a property of stored energy in twisted magnetic fields suddenly being released and accelerating charged plasmas. They can be quite big compared to the diameter of the sun. Most of the material falls back onto the sun but not all of it.

It would have to be a very heavy (and bright younger neighbour) to evolve fast enough to lose control of its atmosphere.

The only situation where that is known to happen are the binary cataclysmic variable stars where typically two very massive stars in fairly close orbits each evolve until one becomes a white dwarf first whilst the other is inflating into a red giant. Eventually the giant can no longer hold onto its atmosphere and it rains down on the dwarf.

I recall a seminar which had the slightly curious title of "Can a young red giant find lasting happiness in the arms of a degenerate dwarf".

Spoiler alert - it does not end well for either of them. But they are interesting objects to observe with amateurs tipping off the professionals whenever any of them come into outburst.

It is a seeming paradox that the heaviest stars burn very bright for the shortest time and the lightest stars smoulder almost forever. The thing that makes the difference is that once you are a certain depth into a star the pressure is sufficient to fuse H+H so massive stars have a huge furnace inside them whilst the lightest stars are just barely alight.

It's strange that the radioisotope concentration in e.g. Moon rock samples seems to indicate that the largest flares haven't been happening with our Sun at anywhere near the rate as it seems they do with the dozens of other "Sun-like" stars studied (if I'm not wrong this is what the article seems to be saying.)

That record must go back even further than the ice core record so it seems odd that our Sun is behaving unusually from a stats perspective over that time. Did we really just get lucky for such a long time? That seems unlikely, too.

the interesting part is that the solar flare can induce a relatively small DC current into the grid transformers, and this small DC offset is what causes them to hit core saturation which leads to problems.

It doesn't just blow a breaker?

From Martin's rather good Royal Academy of Engineering reference, p22...

The induced geoelectric field varies at a frequency that is much less than the network?s operating frequency of 50Hz. Thus, GICs appear as quasi direct currents superimposed on the system?s alternating current. These quasi-DC currents magnetise the transformer core in one polarity and can cause the core to magnetically saturate on one half-cycle of the AC voltage. This half-cycle saturation causes peaks in the magnetising current drawn from the grid system.

The most serious effect of this half-cycle saturation is that when the core saturates, the main magnetic flux is no longer contained in the core. The flux can escape from the core and this can cause rapid heating in the transformer and the production of gases in the insulating oil, which leads to alarms being triggered, shut-down of the transformer, and, in the most severe incidents, serious thermal damage to the transformer. Even if no immediate damage is caused, the performance of the transformer can degrade, and increased failure rates over the following 12 months have been observed [Gaunt and Coetzee, 2007].

The more likely effect, although less serious, arises from voltage instability. Reactive power is required on the grid to maintain voltage. Under conditions of half-cycle saturation, transformers consume more reactive power than under normal conditions. If the increase in reactive power demand becomes too great a voltage collapse can occur leading to a local or, if severe enough, a national blackout.

A third effect arises from the distortion of the magnetising current which becomes non-sinusoidal, and injects harmonics into the grid. Under normal operating conditions, these harmonics are indicators of faults such as negative phase sequences, and the presence of harmonics triggers protective relays. But under GIC conditions the relays can disable equipment, such as static variable compensators, designed to support the voltage on the system, making voltage collapse more likely. It was this triggering of relays that led to the

National Grid experienced distortion of the magnetising current effects on 14 July 1982, 13-14 March 1989, 19-20 October 1989 and

Recently in geological timescales there haven't been all that many big solar flare events to put spikes of C14 into the atmosphere (and they get that from ice cores rather than anything else).

OTOH it is unlikely that life would be around to do astronomy if our star were not fairly stable. Sun-like covers a range of mid sized stars it isn't surprising that some are more variable than others.

Our sun is stable in part because we are here to look at it.

Lower mass stars are typically a bit more volatile with bigger flares and much higher mass stars don't live for long enough. It is a form or anthropic principle in that we are in the Goldilock's position.

By the time the breaker reacts there can already be quite serious damage to the transformers. It's discussed in the RA Eng article I linked to on p22-23. UK isn't all that vulnerable since we are a long way from magnetic north and have relatively short power lines.

USA and Canada are in the firing line and have very long network cables.

Blackouts aren't so bad, if after the severe event, the system can be restarted. What would be really bad is permanent damage, especially if widespread, and not just one transformer here or there.

Just so. I had them repeatedly as a kid, and remember revising for formal exams by candlelight. Those blackouts were principally political, and the disconnection/reconnection times were publicised in advance. That was tolerable.

But if you add in insufficient "local" spares plus a long supply chain, the results over a 6 months timeframe could be /very/ messy.

The RAEng article is worth reading. It is both sober and sobering.

_flare.jpg

You didn't read far enough.

"Or it may be that the Sun?s superflares don?t leave much o f a radioactive trace on Earth. One theory is that a really powerful blast of energetic protons from a superflare could create magnetic waves strong e nough to then scatter the protons, preventing most of them from reaching us , reducing the radioactive fallout."

That would imply that our sun does have superflares, but they don't leave t he traces you'd expect from scaling up the consequences of smaller flares.

Sod's Law would imply that bigger flares would concentrate their high-energ y protons into one needle-like ray that mostly misses us, but Sod's Law is not to be relied on.

The problem is mainly with long wye connected HV-lines in which the star points are connected to local grounding networks. The DC/ULF ground currents will cause a voltage difference in the ground, hence the grounding electrodes are at differential potentials.

Since the wire resistance is much lower than the ground resistance between sites, part of the ground current take a "shortcut" through the transformers and HV lines, causing transformer saturation issues. No such problems with delta connected lines, which do not have (direct, low impedance) ground connections.

Even with a wye connected lines, grounding the star point at only one end of the line and letting the other end star point floating (or through a high impedance to ground) would reduce the problems.

It seems that in some countries (USA/Canada ?) autotransformer are used, so no isolation between primary and secondary and hence a shared star point, so it would be quite risky to float the star point at some transformers.

This has caused some premature blackouts since the protection relays had been set too conservative.

That is the problem if you don't shut the distribution system down cleanly before it gets hit you could lose a lot of very big transformers with extremely long manufacturing lead times all at once.

Back in the days when maglev turbo pumps were the best thing since sliced bread I found myself in the maelstrom that followed a sharp earthquake in the Tokyo area that took out every last one of them.

Note that the preparatory mitigation for a storm involves connecting everything to the grid, so as to attempt to reduce the chance of any one item being overloaded.

Whether that would be successful, sufficient or would lead to cascading failures is TBD :(

From p26... Increased reserves of both active and reactive power would be scheduled to reduce loading on individual transformers and to compensate for the increased reactive power consumption of transformers. Where possible, circuits would be returned from maintenance work, and other outage work postponed, increasing the stability of the system against voltage fluctuations.

Substations would be run to maximize the connectivity of the grid where possible. Large power transfers between areas would be reduced, particularly on the Scottish-English transfer boundary. National Grid would operate an ?all-in? policy where all of its transformers were switched in, reducing the individual neutral current through any one, and all generators would be instructed to generate, reducing the loading on generator transformers, and also increasing reserves.