How is a power grid damaged by a solar storm ?

How is a power grid damaged by a solar storm ?
Posted by opablo on 25 Jul, 2014 17:43
Do Solar Storms Threaten Life as We Know It? --By Steve Tracton
http://voices.washingtonpost.com/capitalweathergang/2009/04/do_solar_storms_threaten_civil.html

Quote
Electric power grids, communications and navigation systems (including GPS), and satellites (including weather) could be damaged beyond repair for many years.

I understand the problems with the satellites but.... power grids ? what's the theory of thinking that they would be affected ?

And of course the rest is a boring Captain Obvious' elaboration of how much we depend on electricity.... boring

But the claim is mentioned in may places...
http://www.reuters.com/article/2012/08/04/us-solar-superstorm-idUSBRE8721K820120804

Quote
A monster blast of geomagnetic particles from the sun could destroy 300 or more of the 2,100 high-voltage transformers that are the backbone of the U.S. electric grid

how ? and if that's so apocalyptic... why can't it be solved with a simple EM shielding ?

http://www.space.com/21805-solar-storms-electrical-grids-research.html
Quote
There is always a small amount of natural electricity running through the ground. Under most circumstances, this electricity is harmless; however, a solar storm can exacerbate the currents underfoot, possible wreaking havoc on electrically linked systems around the world.

I'm supposed to understand that I can have a potential difference of 100.000 V between a power plant's earth net and the one of a city 1000km away from it ?

#1 Reply
Posted by Stebanoid on 25 Jul, 2014 17:52
Solar wind impulses causes changes in Earth's magnetic field that causes high currents in looong grid transmission lines. Not really have calculations but heard somewhere. Looks plausible.

#2 Reply
Posted by jahonen on 25 Jul, 2014 17:55
http://en.wikipedia.org/wiki/Geomagnetically_induced_current

Regards,
Janne

#3 Reply
Posted by opablo on 25 Jul, 2014 17:58
Can't the power grid's transformers be protected with spark-gaps ? used as over-voltage protections ?

#4 Reply
Posted by SeanB on 25 Jul, 2014 18:02
The problem is the very low frequency AC induced saturates the transformers and causes them to fail after they go into saturation. Not high voltage just high current which is not sensed by the line monitoring as that is designed for the grid frequency.

#5 Reply
Posted by djacobow on 25 Jul, 2014 18:07
Quote from: opablo on 25 Jul, 2014 17:58
Can't the power grid's transformers be protected with spark-gaps ? used as over-voltage protections ?

Yes, they can and they are. In fact, most grid components have several layers of protection devices: spark gaps, fuses, breakers, etc.

I can see such solar activity putting certain transmission elements out of service during the event, but I don't buy the widespread damage scenario at all.

There seems to be widespread belief that the power grid is "stupid" and "brittle." Most of this comes from folks with something to sell. The reality is that the grid itself is dumb, but designed carefully and cleverly by pretty smart people who are insanely risk-averse and who will overdesign by huge factors to meet N-1 or N-1-1 or whatever standard is required. (All this said, we do get cascading failures, almost always the result of incorrect coupling of controls.)

#6 Reply
Posted by djacobow on 25 Jul, 2014 18:11
Quote from: SeanB on 25 Jul, 2014 18:02
The problem is the very low frequency AC induced saturates the transformers and causes them to fail after they go into saturation. Not high voltage just high current which is not sensed by the line monitoring as that is designed for the grid frequency.

I can speak from some knowledge of the system in California. There is not much telemetry at lower transmission line voltages (60kV, some 125kV) but just about everything above that has good monitoring of power flows, which includes current and voltage, and protection schemes are designed around the MVA limits of the equipment. There are also a lot of PMUs (phase measurement units) going in which can spot changes in phase between nodes, and would be highly diagnostic in a situation where a transmission line had just turned itself into a very long transformer coupled to the sun's magnetic field.

#7 Reply
Posted by johansen on 25 Jul, 2014 18:15
Quote from: djacobow on 25 Jul, 2014 18:07
Quote from: opablo on 25 Jul, 2014 17:58
Can't the power grid's transformers be protected with spark-gaps ? used as over-voltage protections ?

Yes, they can and they are. In fact, most grid components have several layers of protection devices: spark gaps, fuses, breakers, etc.

no, they aren't. that's the problem.
you have a big loop formed by 200 foot tall wires and the ground. the neutral is grounded on both sides.

geomagnetically induced DC current is on the order of 0-10 volts per mile. this is enough to put triple digit DC amps on top of the ac current, which is on the order of four digits. so its not electrically significant.

the problem is the dc current partly saturates the transformer, and the ac power lost in the core melts things down. the actual current doesn't have to increase much.
furthermore, because these transformers are so efficient, that the partly saturated transformers are often drawing asymetric currents which are naturally present when the transformer is initially turned on.. so guess what.. the filters are already set up to ignore that current.

Additionally many transmission lines have no way of sensing this current because they use ac current transformers on the hot lines, not dc current ct's on the neutral.
so, all you have to do to prevent the transformers from saturating is to put large capacitors in series with the neutral on one or both sides of the transmission lines.
this is estimated to cost 50,000 dollars for each of the biggest 1000 transformers. (because they have to pay an engineer to figure out how big it needs to be lol)
the actual capacitors are only a few thousands.. maybe 10,000 USD for the largest ones.
the utility won't pay for this, they want congress to pay for it. but it is that simple.
you don't need spark gaps across the capacitor (its impedance is lower than a lightning bolt), but a resistor is sufficient.
the capacitor and the resistor have to be able to handle 10 volts dc per mile of transmission line. maybe double that for a once in 1000 year event.

#8 Reply
Posted by djacobow on 25 Jul, 2014 18:25
Quote from: johansen on 25 Jul, 2014 18:15
the problem is the dc current partly saturates the transformer, and the ac power lost in the core melts things down. the actual current doesn't have to increase much.

Aren't the transformers also monitored thermally? The larger ones have rather sophisticated thermal management systems, with oil, pumps, radiators, blowers, etc.

#9 Reply
Posted by opablo on 25 Jul, 2014 18:32
Right... the question is... Is it true that our power grids/transformers/etc are.... vulnerable... today ?

Or is it just a great-selling apocalyptic headlines for news sites and newspapers ?

#10 Reply
Posted by Neilm on 25 Jul, 2014 18:38
Quote from: opablo link=topic=34325.msg485248#msg485248

I'm supposed to understand that I can have a potential difference of 100.000 V between a power plant's earth net and the one of a city 1000km away from it ?

Around big transformers there is an area where you are not allowed to walk, as the potential difference across your feet as you walk is enough to kill / injure you.

There have been many scenarios played out on the subject of solar storms. About all they agree on is that there isn't too much we can do about them. As a worst case, the worst storm would mean the only way to protect the main transformers would be to take them off line prior to the storm hitting. Better a couple of days without power than having to replace some of the big transformers which have lead times of 18 months or more.

#11 Reply
Posted by SeanB on 25 Jul, 2014 18:40
Yes, monitored, but when a large one trips out from DC current the inner core will have gotten very hot to expand oil back into the conservator at a higher rate than daily temperature cycling, so it will need to be inspected to see if the insulation has been degraded. The protection is mostly there to monitor for arc faults that will then trip out the transformer before the unit catches fire. The fans and such are there for normal use where they dissipate the normal heat generated due to the eddy current losses and I2R losses in the windings. They are slow reacting as the large thermal mass is both slow to heat up and even slower to cool down. If it trips from the fault circuitry then it is pretty much mandatory that it will be pulled out of service for draining, untanking and inspection for damage. Even the baby 250kVA unit that feeds me at home was replaced a month ago because of an oil leak on a seal. It will go back into service somewhere else after being inspected and repaired. Some are nearly a century old and still in service.

#12 Reply
Posted by johansen on 25 Jul, 2014 19:09
Quote from: djacobow on 25 Jul, 2014 18:25
Quote from: johansen on 25 Jul, 2014 18:15
the problem is the dc current partly saturates the transformer, and the ac power lost in the core melts things down. the actual current doesn't have to increase much.

Aren't the transformers also monitored thermally? The larger ones have rather sophisticated thermal management systems, with oil, pumps, radiators, blowers, etc.

yes they are monitored thermally, but that is a long time scale.

the problem is the power density of these large transformers is so incredibly high, that if you were to reduce the efficiency from 99.8% down to 98% you would have a melt down within like, all of one minute, and would hardly notice the extra power draw.
yes of course most transformers will be shut off when the oil starts to boil, or arcs generate various gases like hydrogen, but by that time its too late and you'll have to replace entire coil groups.

this problem is not actually that bad, when the transformer saturates most of the heat is generated in local hot spots.
but worst case is the coils will melt down and you won't even notice it until it is too late.

there are instances where the dc current is electrically significant, and has melted wires.. but usually the dc flux causes the ac exciton current to rise to excess.

additionally, the saturated core is going to place high field strengths in local magnetic hot spots filled with 3rd and higher harmonics which will cause eddy current losses in the coil further heating up the coil.

i know that its inconceivable that .1 amps of dc on top of 1 amp of ac excition current in for example a 100 watt toroidal transformer would cause a melt down so quickly.
But These larger transformers are operating well in excess of 1 KVA per kilogram and just 2 watts per kilogram losses. 1 watt for the copper, 1 watt for the core. and that's why they can melt down so quick once something heats up and shorts out. even at 99.8% efficiency, they still run at 40C or more temperature rise.

#13 Reply
Posted by djacobow on 25 Jul, 2014 19:10
Quote from: SeanB on 25 Jul, 2014 18:40
Yes, monitored, but...

Thanks for the detailed explanation. I understand the issue now.

It does sound like a pretty "simple" problem, then, in the sense that what is needed is appropriate monitoring that can send signals to existing protection devices to get them to trigger in an additional circumstance. Of course, it's not simple, because there are so many transformers, they are so spread out, and because many of them were designed as self-contained systems, not ones you can just update the firmware with a new info source.

Utilities love nothing more than to spend money on equipment they can ratebase, so I wonder why they are not pushing harder on these upgrades.

#14 Reply
Posted by SeanB on 25 Jul, 2014 19:21
The 250kVA unit I use is about 5 cubic metres in volume, and about half is cooling oil inside the tank. No protection aside from a set of HRC fuses on the 11kV primary side ( really big fuses though) and the assorted 200A fuses on the output 400VAC 3 phase side. the cabling on the primary side has earth fault relays on it, and this will trip out for arc faults inside the transformer and in the cabling as well.

The steel case is designed to contain the arc pressure for as long as it takes the protection to operate, though this may not always be effective, so the transformer vault is designed to contain the blast as well. The one by me is in an old substation that originally had a DC mains supply for a tram, which was stopped in 1900 or so. There still is the original wiring and terminations for the tram wiring, and a vault for the mercury rectifiers. The lighting is still from that era, with DCC rubber wiring and hanging lamps with the original switches and fuse links still in use. Nice Victorian building as well, though the doors have had to be replaced from the original wood to a steel vandal resistant unit as the copper thieves are very common.

I did pick up 2 of the earth fault monitors at the scrapyard though for scrap value. They were replaced likely as they are 30 years or so old and the original manufacturer no longer exists. The utilities are very loath to spend money on upgrades if there is no immediate value perceived by them. They will happily add cable and transformers along with the standard switchgear so long as there are new customers or increased load on a particular area of the grid that brings in money from billing. Protective devices that are there for a low probability act are not going to be done unless they are upgrading in general in an area and the added function is part of the unit when purchased, or they get it at little to no cost in the contract.

#15 Reply
Posted by johansen on 25 Jul, 2014 19:28
Quote from: SeanB on 25 Jul, 2014 19:21
The 250kVA unit I use is about 5 cubic metres in volume, and about half is cooling oil inside the tank. No protection aside from a set of HRC fuses on the 11kV primary side ( really big fuses though) and the assorted 200A fuses on the output 400VAC 3 phase side. the cabling on the primary side has earth fault relays on it, and this will trip out for arc faults inside the transformer and in the cabling as well.

that transformer may be too small for just 1 volt dc to saturate the core.
you might have fun trying to calculate that out if you can somehow disconnect the primary, put a 12v dc car battery in series and turn it back on.

I do not believe the dc volts generated on a few miles of regular 60 foot high telephone poles will be enough to cause any problems.. also, many larger lines in and around cities are buried.. almost all of the threat is those large east west lines that are 200 and more feet off the ground.

#16 Reply
Posted by SeanB on 25 Jul, 2014 19:39
Yes, the problem is mostly on long lines over 100km long, which typically are 66kV, 132kV and 400kV here. There is a single DC link from Kahora Bassa providing a DC intertie for the SADC grid, which mostly operates well. Distribution is at 33kV or 112kV, so there the problem is not an issue, as the loops formed are too small.

The big transformers though are much fewer in number, and as well typically there will be 1 spare on hand for a group of substations. Thus an incident where you need 2 or more will result in problems as you wait for a repair on the other failed units.

#17 Reply
Posted by Artlav on 25 Jul, 2014 20:17
Forgive me for asking a stupid question, but why wouldn't a blatantly obvious solution of adding (huge) capacitors in series with the transformers work, to block these DC currents?

#18 Reply
Posted by SeanB on 25 Jul, 2014 20:21
Cost, as the capacitor will have to be able to hold massive voltage across it at DC and pass over 1000A at 50/60Hz with minimal loss. It also has to be able to withstand the regular insults that a power line is subjected to.

#19 Reply
Posted by Marco on 25 Jul, 2014 20:34
Quote from: Artlav on 25 Jul, 2014 20:17
Forgive me for asking a stupid question, but why wouldn't a blatantly obvious solution of adding (huge) capacitors in series with the transformers work, to block these DC currents?
I read a while back that Hydro Quebec actually did this after the 1989 event.

#20 Reply
Posted by djacobow on 25 Jul, 2014 21:14
Thanks for this thread. It's always great to think you understand something and then learn that you didn't.

But now I have more questions.

First, with the aid of a magnetometer (or several) and with knowledge of the layout and impedances of the transmission system, is it possible to calculate which lines will be subject to induced currents and then take them out of service? Could be a great business oppty for someone to write the right software, if so? This might require relatively little new hardware.

Regarding the 250kVA xformers like johansens, is it really necessary to protect such relatively small distribution infrastructure? Would not a more sensible approach be to focus only on the more susceptible transmission lines and then take them out of service, shedding the load they serve. This would save the downstream components automatically. I guess the consequence would be that false alarms would effect larger areas.

Regarding whether utilities want to pay for this stuff, I think it depends on how they make money. Most utilities around the country make money by selling energy at a markup, but at least in some territories, like CA they explicitly are disallowed from doing so. Instead, the PUC allows them to make a return on their investments. So, to a first order, they actually do have an interest in installing new capital equipment -- and I can assure you, they have bought some expensive lame stuff over the years. However, politics, and the potential for looking bad by installing unnecessary things forms a second order disincentive that slows the first down considerably.

As it happens, I did a bit of Googling and apparently none of the three major utilities in CA have GIC plans. That could mean they have their fingers in their ears, or they have done analysis that makes them think they're OK, or they've gotten the signal from the PUC that they're not interested, or that they believe that they have protection systems in place now that are adequate. I have a friend who is a transmission planner at PG&E. I'll ask him next time I see him.

#21 Reply
Posted by johansen on 25 Jul, 2014 21:15
i said in my first post in this thread that capacitors are the solution..
they are also cheap.

a few thousand dollars per substation. plus 20 thousand for an engineer to put his fat stamp on it.

the grid already spends millions on power factor correction capacitors.. it really is no significant expense for them.
yes, its a different technology.. you need thousand volt capacitors at thousands of uf, rather than ten thousands or hundreds of thousands of volts.
but the actual volume of energy storage.. a 5 gallon bucket sized capacitor... seriously guys. they could actually let the neutral float and get away with it.

#22 Reply
Posted by Tinkerer on 25 Jul, 2014 22:57
One thing you need to take into account is everything connected to the power grid, not just the transformers. This includes refridgeration systems which are responsible for keeping alot of food so people dont starve as well as water pumps and so people have something to drink. Knock out a major portion of this and you better hope it can be fixed in 2-3 days before a huge number of people start marauding around trying to get food and water.
Although, the transformers themselves they dont leave extras laying around. Take out a few of them and major portions of the power grid are disrupted. They can take up to 2 years to build as well.

#23 Reply
Posted by edpalmer42 on 25 Jul, 2014 23:01
Quote from: Neilm on 25 Jul, 2014 18:38

There have been many scenarios played out on the subject of solar storms. About all they agree on is that there isn't too much we can do about them. As a worst case, the worst storm would mean the only way to protect the main transformers would be to take them off line prior to the storm hitting. Better a couple of days without power than having to replace some of the big transformers which have lead times of 18 months or more.

And don't forget that the 18 month lead time is under normal conditions. What's the lead time going to be when power companies all over the continent (or further?) are all screaming for new transformers? 2 years? 5 years?

Ed

#24 Reply
Posted by dannyf on 25 Jul, 2014 23:57
-I'm supposed to understand that ...-

I think the issue is that you are trying to understand an issue that requires faith.