Global Geomagnetic Storm
Induced Failure of 400 Mega-HVAC
Transformers is Avoidable by
Redundant HVAC Transformer Arrays
- or -
A Current and Voltage Division Method to Reduce Mega-HVAC
Transformer Failures by Redundant Transformer Arrays
Abstract
During severe solar storms HVAC transformers used by utilities of
dimensional size similar to a medium sized house are subject to catastrophic
failure. As these transformers have very long commissioning and repair
schedules their failure poses a catastrophic risk. Large parts of grids that
depend on their existence of these AC transformers can be rendered
non-functioning when the mega transformers fail. This catastrophe can be
avoided by using simple voltage division and current division principals
implemented in the form of redundant arrays of smaller HVAC transformers.
Electric power is modern society's cornerstone technology on which
virtually all other infrastructures and services depend. Yet HVAC power
grids are particularly vulnerable to space weather events.
Ground currents induced during geomagnetic storms can create excess
currents in the electrical grid. These excess unregulated currents have
the power to melt the copper windings of electrically stressed
transformers at the core of many mains power distribution systems.
Sprawling power lines in essence act like VLF antennas. The grid's
distribution network picks up the induced currents created by the solar
storm and absorbs them [at full energy] into the power grid.
Mechanisms
A time-varying magnetic field external to the Earth induces electric
currents in the conducting ground.
These currents create a secondary (internal) magnetic field.
As a consequence of Faraday "Law of Induction" electric fields aligned
along the surface of the Earth are induced in association with the time
variations of the magnetic field. The surface electric field causes
electrical currents that are known as Geomagnetically Induced Currents
(GICs) to flow into any conducting structure.
This GIC induced electric field (typically measured in V/km) acts as a
voltage source across networks.
Examples of Geomagnetically Induced Current conducting networks are
- electrical power transmission grids
- oil and gas pipelines
- undersea communication cables
- copper telephone networks
- telegraph networks used by railways
GICs are often described as being 'quasi Direct Current' (DC) although
the variation frequency of GIC is governed by the local time variations
of the Earth's electric field. Geomagnetically Induced Currents in the
systems that conduct them are more like DC bias currents. For GICs
to be a hazard to technology, the current flows have to be of a
magnitude and frequency that makes electrical equipment susceptible to
either immediate or cumulative damage.
The size of the GIC in any network is governed by the electrical
properties and the topology of the network. The largest (magnetospheric)
ionospheric current variations, resulting in the largest external
magnetic field variations typically occur during geomagnetic storms.
Geomagnetic storms by their nature create the largest GICs.
Significant temporal variation in GICs is known to range from from a few
seconds to about an hour.
Since the largest magnetic field variations are observed at higher
magnetic latitudes, GIC have been regularly measured in Canadian,
Finnish and Scandinavian power grids and pipelines since the 1970s.
GICs of tens to hundreds of Amperes have been recorded outside the Polar
regions. GICs have also been recorded at mid-latitudes during major
geomagnetic storms with nearly the same magnitude as the GICs in Polar
regions. However, GICs are not a problem exclusive to the mid-latitudes
or the Arctic.
There is still a substantial GIC risk to low latitude areas (the
tropics). When a geomagnetic storm commences suddenly -- a high,
short-period rate of change of the Earth's magnetic field will occur on
the dayside of the Earth. This sudden induction event will induce high
current GICs into the tropic regions. These events are typically short
lived, but pose a threat to the power supply systems in the tropics.
The problem
According to a study by Metatech corporation, a geomagnetic storm with a
strength comparative to that of 1921 would result in at least 130
million people without electrical power and 350 broken HVAC
transformers. The overall cost of restoring the grid to its original
functionality and the economic damage caused by the disruption would be
around 2 Trillion Dollars (2 000 000 000 000 USD).
Power distribution grids are not designed to absorb large scale
geomagnetically induced currents as part of their normal day to day
operation.
Modern electric power transmission systems consist of generating plants
interconnected by electrical circuits that operate at fixed transmission
voltages controlled at substations. The grid voltages employed are
largely dependent on the path length between these substations.
Typically 200kV to 700kV system voltages are common.
There is a trend towards higher voltages and lower line resistances to
reduce transmission losses over longer and longer path lengths. Low line
resistances produce a situation favourable to the flow of GICs.
Power transformers typically have a magnetic circuit that is disrupted
by the quasi-DC GIC: the field produced by the GIC offsets the operating
point of the magnetic circuit and the transformer may go into half-cycle
saturation. This produces harmonics to the AC waveform, localized
heating and leads to high reactive power demands, inefficient power
transmission and possible failure or abnormal operation of protective
devices.
Balancing the electrical network in such situations requires significant
additional reactive power capacity.
The magnitude of GIC that will cause significant problems to
transformers varies with transformer type. Modern industry practice is
to specify GIC tolerance levels on new transformers.
There are some partial solutions for coping with geomagnetically induced
currents, typically involving grounding the electrical grid at
- 50 km intervals in the latitude [North-South] domain
- 75 km intervals in the longitude
[East-West] domain
- longer intervals than 60 km closer to the tropics
It must be noted that most electrical utilities often fail to
fully implement these recommendations.
GIC risk can, to some extent, be reduced by capacitor blocking systems,
maintenance schedule changes, additional on-demand generating capacity,
and ultimately the policy of load shedding.
These options are expensive and sometimes impractical.
The continued growth of high voltage power networks results in a higher
risk for all users. This is partly due to the increase in the
interconnectedness at higher voltages; connections in terms of power
transmission to grids in the auroral zone, and grids operating closer to
capacity than in the past.
To understand the flow of GICs in power grids and to advise on GIC risk
analysis of the quasi-DC properties of the grid is necessary. This
analysis must be coupled with a geophysical model of the Earth that
provides the driving surface electric field, determined by combining
time-varying ionospheric source fields and a conductivity model of the
Earth.
This kind of analysis has been performed for North America, the UK and
in Northern Europe. The complexity of power grids, the source
ionospheric current systems and the 3D ground conductivity make an
accurate analysis difficult but not computationally impractical. By
being able to analyze major storms and their consequences it is possible
to build a picture of the weak spots in a transmission system and run
hypothetical event scenarios.
The perils of interconnection
From the 1990s into the present day US utilities have joined grids
together to allow long-distance transmission of low-cost power to areas
of sudden demand. Canada is also part of this North American electrical
grid network, a fact often lost in the technical literature. Canada is
even more susceptible to coupled Winter storm + Geomagnetic storm
conditions. In Canada, substantial loss of life is possible due to a
grid failure's direct effects. In the US the secondary effects of grid
failure will lead to larger per capita loss of life than Canada via
primary effects.
As it were : on a hot summer day in California, for instance, people in
Los Angeles might be running their air conditioners on power routed from
Oregon. This may make short term economic sense -- but not necessarily
geomagnetic sense. Grid interconnectedness makes the power distribution
network susceptible to wide-ranging "cascade failures."
The problem
These power grid failure problems are totally 'man made' and are 'design
induced problems' with several different and notable causes
- State or private sector companies have been hiring
electrical engineers for decades that are barely suitable to the
task of maintaining the power grid. Of the subtle problem solving
issues and complications required in real electrical engineering
these engineers know not a jot.
- Nepotism, favoritism [coupled with a hefty dose of outright
class and race discrimination] at virtually every electrical
engineering school in North America has in effect left this part of
the electrical engineering profession (that maintains the essential
functioning of the power grid) with poor or unsuitable replacements.
- The 'classically trained' North American electrical
engineers of the 1950s to the 1970s are far better problem solvers
than their existing counterparts today.
- It must be noted that the education system in the US
functioned adequately enough during the 1950s to 1970s to produce
suitable grid engineers capable of some original thought and
innovations.
- The exiting of these engineers via retirement will be felt
in the 2010s with a drop in overall reliability of the US
electrical power grid.
- Although the education situation in Canada may be better
than the US's, Canada has neglected this vital profession in spite
of the ongoing threats to grid reliability that pervade Canada's
geographic space.
- The finance system that oversees the funding of utilities in
North America has not encouraged innovations in grid reliability.
This finance sector neglect is a global problem -- and probably a
principal reason why the HVAC transformer redundancy problem was not
solved globally at least 30 years ago.
- Governmental regulation at all levels in North America has
failed to address the problem of Mega-HVAC failures directly or
indirectly, effectively perpetuating the problem by neglect.
- Computational research into the known problems of large
scale AC transformer circuit grids could have fixed the problem by
the late 1990s. It is clear that limited power grid circuit
re-design is would be needed but the problem is not a complex one.
- There is an ongoing failure by all parties involved to make
the HVAC Transformer problem and its solutions 'open source' so as
to encourage ongoing research.
- An outright disregard for electrical engineering, chemistry
and physics knowledge by the general public in North America as well
as substantial parts of Europe.
Tentative recommendations for making power grids
survive severe solar storms
General system recommendations and practices
- Generally the transformer redundancy rule should be
- [small-odd-number-under-eleven] = Number of Redundant
Transformers.
- Generally the transformer redundancy rule should be
- [small-odd-number-under-eleven -1] = Number of Redundant
Transformers in Use (at any one time to backup the Mega-HVAC
transformer).
- Potentially up to 13 HVAC transformers could be used in
parallel -- but the buffering and cophasing networks as well as
safety considerations might make such a system too complex.
- There are personnel safety system issues involved with using
an array of more than 11 transformers.
- The excess redundancy of an array of 13 HVAC transformers is
only recommended for the most northerly locations or extreme
engineering conditions.
- Each HVAC transformer must have its own accompanying
buffering and matching network to terminate and match its output.
- It is not fully clear exactly how this HVAC transformer
network should be designed. There are at least 400 different
Mega-HVAC transformer installations -- and each may be locally
unique. Let it be said that the required AC (matching / cophasing)
networks are not design impossibilities for this kind of
application.
- In principal as well as in practice: It is not recommended
risking going below 5 redundant HVAC transformers, with 7 being the
nominal recommendation.
- The ultimate number of redundant transformers must
ultimately depend on the static and dynamic load factors for the
Mega-HVAC transformer.
- Overall recommendations on redundancy : an array of 11 to 7
transformers is nominal.
Specific system recommendations and practices, typical transformer
redundancy mode of 7
- Each Mega-HVAC transformer must have [as a backup system] an
array of at least 7 HVAC transformers (6 in use at any one time)
that can be switched on as a backup system at any time.
- At least one redundant HVAC transformer array element must
always be in 'repair or maintenance mode' or 'storm buffering mode
set aside'.
- Each redundant HVAC transformer must be rated at 1/6th the
combined Mega-HVAC (input/output) parameters, where an array of 7
transformers exist.
- The individual HVAC redundant transformer array ratings
should be 133% to 166% of the [(1/6th) x (Mega-HVAC-ratings)]. A
solar storm may happen when a redundant transformer is set aside for
repair, thus the 1/6th not 1/7th constant.
Operation modes
- This technology will have [by necessity] at least 3 to 5
common operating modes.
- A (single input, two output) variable potentiometer must
proceed the Mega-HVAC Transformer and its backup redundant array of
transformers that splitting the input load.
- A variable potentiometer to split the voltage and current
between the original HVAC mega transformer and the redundant array
must under normal conditions be balancing the loads at (50%, 50%).
- The variable potentiometer must [under stressful solar storm
conditions] reduce the load going into the Mega HVAC transformer by
at least 25% (75%, 25%) but also be able to do so by up to 45% (95%,
5%).
Redundant Transformer Array State
Machine Operating Modes
- Mode # (Input into Array, Input into Mega Transformer)
- Mode 1 : (50%, 50%) : nominal operations
- Mode 2 : (75%, 25%) : the redundant HVAC array is made
backup to keep the HVAC from failing
- Mode 3 : (100%, 0%) : this is a
maintenance mode not a normal operations mode.
- Mode 4 : (0%, 100%) : this is a maintenance mode not a
normal operations mode.
- Mode 5 : (90%, 10%) : in the long term, the Mega
Transformer should be used as a secondary backup until it is time
for it to be decommissioned.
Operation Modes (Notes)
- Mode switching time must be kept at 1 hour during the Winter
and 3 hours during the Summer, with most repairs to the redundant
arrays being made during the Fall and Spring.
- A cophasing and buffering network after the [redundant
array] or after the [redundant array + mega HVAC transformer] is
needed to restore the required target output voltages and amperages
to the mains grid.
- It is not recommended to operate in INPUT-OUTPUT SYMMETRY
MODE where 1 HVAC = 1 HVAC (input, output symmetry) unless there is
an absolute engineering necessity -- except in the form of 1 HVAC
input = 2 HVAC outputs.
- Arbitrarily engaging in engineering practices that force
more Mega-HVAC transformers into existence in the existing
electrical grids [except to increase the reliability of those
already deployed] has engineering and reliability limitations.
- Many Mega-HVAC transformers that are currently deployed may
not have any actual engineering necessity, with respect to alternate
grid designs that could be put into place that would alleviate their
existence entirely.
- It is assumed that the Mega HVAC transformers will
eventually be phased out by redundant arrays of cheaper HVAC
transformers so as to totally eliminate this failure mode.
- High power diodes to keep the AC currents unidirectional
will be requried in any HVAC redundant array design. Redundant
arrays of analogue devices must be designed so as to avoid current
feedback and reflection problems.
- Circuit breakers to separate out the transformers from the
array and grid must be 4x redundant so as to make accidental
energizing of the transformer nearly impossible.
Why the above recommendations will work, or the electrical
engineering laws we know so well
- The current entering any junction is equal to the current
leaving that junction : aka Kirchhoff's current law (KCL).
- The directed sum of the electrical potential differences
around any closed circuit must be zero. (Note that geomagnetic
storms tend to disturb this difference to destructive effect within
the innards of transformers.)
- In electrical circuit theory, Thévenin's theorem for linear
electrical networks states that any combination of voltage sources,
current sources and resistors with two terminals is electrically
equivalent to a single voltage source V and a single series resistor
R. For single frequency AC systems the theorem can also be applied
to general impedances, not just resistors. This simple principal can
simplify the conceptual and practical problems that will be
encountered along the way.
- Norton's theorem for linear electrical networks states that
any collection of voltage sources, current sources, and resistors
with two terminals is electrically equivalent to an ideal current
source, I, in parallel with a single resistor, R. For
single-frequency AC systems [like power grids] the theorem can also
be applied to general impedances, not just resistors.
- The Norton Equivalent is used to represent any network of
linear sources and impedances, at a given frequency. The circuit
consists of an ideal current source in parallel with an ideal
impedance (or resistor for non-reactive circuits).
Recommendations for Australia, Canada & New Zealand
- Australia should make the necessary changes in its AC grids
in the next 5 years, as the budgets permit at the electrical
utilities. Australia has a lot of isolated AC power grids, so most
of the Australian AC power grid may not be affected by the induced
currents problem to any extent. Australia may have less than 4
Mega-HVAC transformers that may be affected by the geomagnetic storm
problem, so time and care can be taken to fix the problem. Local
HVAC grid Solar and Wind power production must be increased to
provide a safety margin. There is no reason the induced currents
problem cannot be fixed by 2013 at the latest, to cope with the
expected solar activity uptick.
- Canada needs to demand that all US based mega transformers
that send power into Canada be redundant as part of any electricity
sales to the US. Domestically, a similar assessment to the US is
needed and a 7 year replacement programme needs to be started with
particular emphasis on Ontario, Quebec and British Columbia.
- New Zealand needs to statutorily make 14 days per year (in 4
separate months) when the North-South HVDC-HVDC grids run totally
independent of each other. Transpower [or any entity involved in
power distribution] needs to institute a redundancy programme for
its suspected HVAC transformers at risk over the next 5 years. As
HVDC is used for long distance interconnects, some experimentation
may be needed to solve the issue. However, with NZ HVDC gird -- the
induced currents problem is far simpler and NZ to fix. New Zealand
may not have any more than 3 HVAC transformers at substantial or
substantive risk.
Recommendations for the European Union
Definitions
- Mega-HVAC Transformer : The rating of the 300 or so in the US is
unknown to me, so the metric of commissioning time will be used. If a
transformer takes more than 6 months (180 days) to build (from
commissioning to delivery) then it is a Mega Transformer.
- Redundant HVAC Transformer : It is assumed that each one of these must
take no more than 3 months (90 days) from commissioning to delivery.
These also must be of a size where one can be physically delivered
anywhere in Europe or North America in 30 days.
- Matching or Cophasing Network : This network is needed to take the
multiple redundant array of HVAC transformer inputs and linearly sum
these inputs into one or two outputs with properly matched: frequency,
phase, amplitude and impudence.
Technical references
Physics
Specific Solar Storm Events
Electrical Engineering
Circuit Analysis
- Linear circuit
(power grids have or develop many non-linear behaviours when extended
beyond 100km as a general rule)
- Mesh analysis
(important for understanding power grid behaviours and risk points)
- Source
transformation ()
- SPICE (Simulation
Program with Integrated Circuit Emphasis)
Power Grid Issues
Power Outage Issues
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Created by |
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Original Idea |
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Created |
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Last Modified |
Version |
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Revision State
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Max Power |
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15 May 2006 |
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24 October 2009 |
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22 May 2014 (readability, content)
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0.87a |
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Revisable
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