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's Law of Induction, an electric field at
the surface of the Earth is 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 GIC conducting networks are: electrical power transmission
grids, oil and gas pipelines, undersea communication cables, telephone
and telegraph networks and 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. 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 occour
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 favorable 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 mis-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%).
- 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 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.
- I do not recommend 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 analog 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
Power Grid Issues
Power Outage Issues
Created by : Max Power / Original idea
: 15 May 2006 / Created : 24 October 2009 / Last Modified : 22
August 2010
