Power June 2023 - 5

SPEAKING OF POWER
Inertia and the Power Grid:
Should We Be Worried
About System Stability?
Aaron Larson
O
ne concern some observers raise
about the growth of inverter-based
resources, such as solar, wind,
and battery storage, supplying the power
grid is that they don't provide inertia. Inertia
has historically been a key source of
grid reliability.
Inertia in power systems refers to the
energy stored in large rotating generators
and some industrial motors, which
gives them the tendency to remain rotating.
Conventional fossil, nuclear, and
hydropower generators provide abundant
inertia, and thus, it has long been
taken for granted that sufficient inertia
would be available for stable and reliable
system operation.
If a large power generator trips offline
due to a fault or malfunction, the
inertia contained in other large generators
synchronized to the grid can temporarily
make up for the power lost from
the failed generator. This temporary response-which
is typically available for
a few seconds-keeps grid frequency
more stable while allowing mechanical
systems that control most power plants
time to detect and respond to the failure.
Measuring Inertia
Because inertia is so important for grid
operation, Reactive Technologies, a grid
resilience tech company, created what it
calls a " first-of-its-kind grid inertia measurement
tool. " Reactive's GridMetrix
platform " provides new levels of visibility
to grid operators, " according to the company,
replacing estimates and modeling
of inertia and other functions, " enabling
better planning for reliability and high utilization
of renewable power. " A trial project
featuring the technology is currently
slated for deployment in Australia.
" Until recently, operators relied on
modeling and estimations to ensure
the grid remained stable, " Marc Borrett,
CEO and co-founder of Reactive Technologies,
told POWER. He explained that
Reactive's pioneering technology directly
measures inertia and system strength
by sending pulses of power through the
grid, which are measured and processed
June 2023 | POWER
by the company's grid edge measurement
devices and its GridMetrix cloud
computing platform.
" Using GridMetrix, operators can now
accurately map any deviations in power
system stability, allowing an almost instantaneous
response to keep the grid
secure, " Borrett said. " The GridMetrix
technology is completely unique in the
industry and is the only solution capable
of measuring inertia and system
strength levels in real-time. Through realtime
measurement, significant value can
be unlocked for grid operators. "
Borrett further explained, " By now being
able to measure the entire energy
system, that is, beyond the transmission
system infrastructure and into the parts
of the network with non-synchronous
generation
and
demand-side
loads,
Reactive makes it possible to directly
measure the hidden inertia in the distribution
grid, which in some cases can
account for up to 30% of the total share
of inertia. Directly measuring this hidden
capacity creates extra capacity for grid
operators to now safely use to integrate
more renewables and, as a result, help
to enable a safer, faster transition to an
ultra-low-carbon power grid while maintaining
system stability. "
Speed of Detection and Response
Is the Key
Yet, according to a technical report published
by the National Renewable Energy
Laboratory (NREL), decreasing levels of
inertia may not be as big of a problem as
some people suggest. The report, titled
Inertia and the Power Grid: A Guide Without
the Spin, explains that inertia is only
one of several grid services that help
maintain power system reliability. " The
importance of inertia to a power system
depends on many factors, including the
size of the grid and how quickly generators
in the grid can detect and respond
to imbalances. A grid with slower generators
needs more inertia to maintain
reliability than a grid that can respond
quickly, " the report says.
One of the key takeaways from the report
is that inverter-based resources have
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the ability to quickly detect frequency deviations
and respond to system imbalances
using power electronics. " Tapping into
electronic-based resources for this 'fast
frequency response' can enable response
rates many times faster than traditional
mechanical response from conventional
generators, thereby reducing the need for
inertia, " the authors explained.
Furthermore, there are two counterbalancing
effects of replacing conventional
generators with inverter-based resources.
While inverter-based resources decrease
the amount of inertia available, they also
reduce the amount of inertia actually
needed, which offsets the first effect. " In
combination, this represents a paradigm
shift in how we think about providing frequency
response, " the report notes.
The NREL report says ongoing research
" points to the possibility of maintaining
grid frequency even in systems
with very low or no inertia. " The development
of new " grid-forming " inverters
enable inverter-based resources to take a
more active role in maintaining reliability
and could be an integral technology for
" a purely inverter-based grid. "
In the meantime, Reactive's Borrett
said his company's technology is uncovering
other important grid management information
that could assist operators. " As
Reactive works with increasingly more
and more grid operators around the world,
its measurement systems are increasingly
able to identify further phenomena,
which have otherwise been hidden or
undetectable, leading to an increasingly
deeper understanding of what it will take
to decarbonize the power system while
maintaining security and reliability. "
The big takeaway is that although
growth in inverter-based resources will
reduce the amount of grid inertia, there
are multiple solutions for maintaining or
improving system reliability. Therefore,
declines in inertia do not pose significant
technical or economic barriers to significant
growth in wind, solar, and storage,
and do not gravely threaten the reliability
and stability of the U.S. power grid. ■
-Aaron Larson is POWER's
executive editor.
5
http://www.powermag.com
Power June 2023

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