This Episode of Real Engineering is brought to you by Shopify. My trusted partner for
merch sales. On July 19th, 2012 the Solar Dynamics Observatory
captured this incredible footage of Sun. This clip was recorded with 1 frame every 12 seconds.
Meaning every second of this video represents 6 minutes of real time. This event began with
an intense solar flare. A sudden release of magnetic energy sending ungodly amounts of
energy, in the form of radiation and light, into space. This particular solar flare was
followed by a coronal mass ejection, a massive twisted bubble shaped eruption firing a colossal
cloud of electrically charged particles into space, which can disrupt interplanetary magnetic
fields and interact with Earth’s magnetic field in what is known as a geomagnetic storm.
Finally, as the solar storm subsided and the eruption bubble began to cool, we were treated
to one of the most mesmerizing events in our solar system. Coronal Rain. Where the remaining
charged plasma cools and falls back to the surface of the sun. Forming these beautiful
cage like structures as the particles follow the Sun’s magnetic field lines back down.
[1] An astoundingly beautiful event, but had it
happened just a week earlier the flare up would have been pointing squarely at earth
and could have had some nasty consequences [2], and it wouldn’t have been the first
time a solar storm affected life negatively on earth.
In 1859 a similarly powerful solar flare, called the Carrington event, did hit earth.
Treating people as far south as the Carribean to the northern lights, while also knocking
out major telegraph systems in both Europe and North America.[3]
In some cases the geomagnetic disturbances were so strong that they sparked fires, shocked
telegraph operators and even allowed the telegraph system to work with no power.
In 1989 a large geomagnetic storm caused a blackout in Quebec after the coronal mass
ejection managed to trip circuit breakers in their grid. Leaving 6 million people without
power for 9 hours. So, clearly these storms have the power to
really mess with vital technologies that keep our society moving, but how exactly do they
do it? [4][5]
To understand this we first need to understand some basics of how electricity is generated
in power stations. As you probably know already, we generate electricity by moving a wire through
a magnetic field, or vica versa. The basic law behind this is called Faraday’s Law[6],
which states that “any change to a magnetic field surrounding a coil of wire will cause
an electromotive force to be produced, otherwise known as a voltage. The voltage can be considered
the force pushing electrons through a wire, if they are free to move a current is produced.
The current is a measure of the rate of flow of electrons.
We generally generate electricity by rotating a coil of wire inside a magnetic field. We
do it this way simply because rotational motion is efficient with no changing of direction
like linear motion forcing us to decelerate and lose inertia, but we can generate currents
other ways, like dropping a magnet through a coil of wire. This moves the magnetic field
itself, rather than the coil of wire. So stationary wires can generate currents
when a magnetic field changes around them, and our electricity grid happens to be made
up of millions of kilometres of stationary wire. We have effectively turned the planet
into a massive electric generator by surrounding the earth’s magnetic core with all this
conductive wire, the only thing that’s missing is a large shift in the earth’s magnetic
field. Unfortunately for us, that is exactly what coronal mass ejections do to Earth’s
magnetic field.
On March 10th 1989, the sun blasted a cloud of charged particles so large that it dwarfed
our planet in size. It raced through space at 450 kilometres per second, before crashing
into the Earth’s magnetopause. The boundary between Earth’s magnetosphere and interplanetary
space, sitting about sixty five thousand kilometres above Earth. It struck with such force that
it literally shook and trembled our planet’s protective magnetic field. [7]
The first phase of this is called the sudden storm commencement where the coronal mass
ejection first arrives at our magnetopause causing the magnetosphere to compress on the
daylight side of the earth. Resulting in a sudden increase in the intensity of the geomagnetic
field in that region. The next phase results in a decrease in intensity as an electric
current induced in the magnetosphere and ionosphere, pushes the boundary of the magnetosphere outwards
and results in a decrease in geomagnetic field, and the geomagnetic field can continue to
vary from hours to days after this initial burst.
So these geomagnetic storms cause shifts in the earth's magnetic field which drives induced
electric currents in anything capable of carrying them. That can be the ground, ocean, or our
electricity grid. If those currents enter our grid they can wreak havoc on essential
infrastructure. So it seems like a disaster waiting to happen.
What are we doing to prepare for the worst? Unsurprisingly, one of the largest industries
on Earth has thought pretty hard about this problem and has set out guidelines on how
to deal with such an event. As mentioned in my recent solar sailing video, we currently
have several satellites parked in lagrange point one. A point between the Sun and the
Earth where a satellite can maintain a constant position, and thus allow us to receive advance
warning of any coronal mass ejection. This point confused many commenters, who assumed
solar flares were simply bursts of radiation travelling at the speed of light, and thus
no speed of light communication method could give us any advance warning.
But these eruptions of particles travel at a fraction the speed of light, about 0.15%
the speed of light for our above 1989 event. (1.48x10-3) And thus can provide up to an
hour of warning time. We also have some other less definitive warning
signs that the Sun may point a coronal mass ejection in our direction by observing sunspots,
which are dips in brightness on the surface of the Sun, which occur as magnetic energy
bottles up in the solar atmosphere before being suddenly released. These sunspots come
in cycles of low and high activity every eleven years.
This warning time can provide grid operators a little time to prepare for any anomalies,
but they are more useful to GPS satellites whose accuracy is affected by ionosphere disturbances
as their radio waves refract through it [10] and thus need to adjust their signal to compensate
for. In severe solar storms these warnings would give industries where GPS malfunction
could lead to loss of life, like airliners, vital time to prepare.
To protect our grid, it’s really a matter of designing it in a way to be able to deal
with these induced currents. Let’s take a deeper look into that 1989 blackout to see
what really happened and see how grid operators can prepare.
The first malfunction occurred as a result of transformers becoming saturated. Power
transformers are placed at internals between high-voltage transmission lines and power
generators or local distribution lines to step-up or step-down voltages.
So what does saturation mean? Transformers work by winding wire from the source around
a ferromagnetic core. This generates a magnetic field inside the core which can in turn induce
an electric current in our secondary winding. If our primary wire has more windings that
the secondary wire it will step down the voltage, and if the secondary wire has more windings
that the primary wire it will step up the voltage. These transformers form an essential
part of our grid, but when the core becomes saturated it interferes with their operation.
Saturation just means that the magnetic core has reached is maximum magnetic flux capabilities,
so an increase in current and voltage will not result in a subsequent increase of magnetic
flux. If this happens, the voltage induced in the secondary winding can no longer match
the waveform as the voltage powering the primary coil. So the waveform of the secondary wire
becomes distorted. [12] When this happened in Quebec the grid voltage
became unstable causing protective relays to disconnect five high-voltage transmission
lines including one from a hydroelectric facility. [12]
As the hydroelectric facility was disconnected it experienced a rapid loss of load, meaning
it’s power had nowhere to go, which caused the voltage to suddenly increase which damaged
two step-up transformers as a result of excessive heating.
Saturated transformers are the route cause of most grid malfunctions during magnetic
storms. However In 1989, the knock-on effect of these waveform distortions is what caused
the majority of the damage, as electro-mechanical protective relays tripped and cut off sections
of the grid. [13]
Electro-mechanical relays are essentially switches that turn on and off when an electric
current flows in the control circuit creating a magnetic field in an electromagnet and pulls
an armature down to complete a circuit in a secondary circuit.
These can be combined to form logic gates that are more complicated, but are in-general
not programmable to deal with anomalies like distorted waveforms caused by transformer
saturation. Today we have much smarter microprocessor
technology that can be programmed to deal with these issues better and maintain grid
stability, but because of the electro-mechanical relay’s reliability and long service life,
there are still thousands of these older devices in the grid infrastructure, but they are slowly
being phased out for more modern technology especially in northern and southern regions
more susceptible to geomagnetically induced currents.
We can also block geomagnetically induced currents because they are direct currents,
where our normal power is alternating current. Capacitors can only transmit alternating current
because capacitors don’t physically complete circuits. They are just large stores of positive
and negative potentials that switch every time the current flips. DC currents don’t
flip and thus a capacitors do not allow DC currents to flow. So we do have options to
minimise the effects of these disturbances. I expected this to be a dramatic video that
would drag viewers in on fear of their grid failing from solar flares. You can probably
tell from the shift in tone from the start of the video to the end, as I researched this
topic more thoroughly. It really seems like mainstream media’s fear mongering on the
effects of solar storms on our electricity grid is completely overblown. With only one
notable blackout caused by geomagnetically induced currents, that with today’s technologies
was completely preventable, there isn’t much evidence that grid operators need to
spend vast amounts of money on these systems. Although DC blocking capacitor systems have
been installed in countries in northern locations more at risk of geomagnetic disturbances,
like Finland and England. [13] In the end the only reason electricity grid
operators have not implemented these DC blocking devices and other mitigating technologies
is because they would cost more to model and implement than the risk geomagnetic disturbances
actually pose to the grid. In reality, the risk from hurricanes and other terrestrial
weather events pose a much bigger risk to our electricity grid.
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