Power June 2023 - 33

RELIABILITY & RESILIENCY
Rethinking Energy Reliability
with Modern Power Systems
As the energy transition to inverter-based resources continues, reliability risk increases
and requires additional investment to mitigate threats. But what measures should
be put in place, what are the associated costs, and how can the power generation
industry budget accordingly?
John F. Peiserich; John Dulude, PE;
Edo Macan; and Chris Norris
T
he Federal Energy Regulatory Commission
(FERC) recognizes that
inverter-based
resources
(IBRs),
in the form of utility-scale wind, solar,
and battery resources connected to the
bulk power system (BPS), have direct
reliability impacts to the overall system.
On Nov. 17, 2022, FERC issued two orders
and published a Notice of Proposed
Rulemaking related to concerns over reliability
gaps associated with IBRs.
Meanwhile, the North American Electric
Reliability Corp. (NERC) has investigated
a series of " disturbances " that
involve the widespread reduction (that
is, loss of generation) of IBRs to identify
systemic reliability issues. The " 2022
Odessa Disturbance " report, a joint
NERC and Texas RE staff report issued
in December 2022, highlighted the significant
risk to BPS reliability, issued immediate
calls to action to enhance NERC
standards for IBRs, and pushed NERC
Reliability Standard enforcement.
To assure the effective and efficient
reduction of risks to the reliability and security
of the power grid, NERC develops
and enforces Reliability Standards; annually
assesses seasonal and long-term
reliability; monitors the BPS through
system
awareness;
and
educates,
trains, and certifies industry personnel.
The NERC Reliability Standards define
the reliability requirements for planning
and operating the North American BPS.
Those requirements apply to IBRs, and
through the proposed rulemaking, will
reach further downstream to increasingly
smaller power generation facilities.
Energy Resilience and Reliability
Simply put, resilience for an electrical
system is its ability to withstand adverse
events without sustained interruptions
of service to customers. Resilience is
largely about what does not happen to
the grid or electric consumers. ReliabilJune
2023 | POWER
1. Reliability versus Black Sky events. Source: Lawrence Berkeley National Laboratory
ity, on the other hand, is a measure of
behavior once resilience is broken. The
start of a sustained interruption is the
transition point from the domain of resilience
to the domain of reliability.
The challenge of energy transition continues
to be maintaining the correct mix
of fuel-based generation with IBRs that
will have both the capacity as well as
the duration to meet load requirements
throughout various demand scenarios. A
few challenges associated with this transition
process include the loss of system
inertia or momentum, as large conventional
prime movers such as turbine-driven
generators are retired and removed from
the grid, and a lack of reactive power, also
known as volt ampere reactive (VAR) that
is necessary for grid operations.
System inertia supports sudden
changes in system frequency driven by
fluctuations in electrical demand. Small
deviations in both BPS voltage and frequency
can potentially lead to significant
system impacts. Inertia behaves a bit
like the shock absorbers in a car's suspension,
which dampen the effect of a
sudden bump in the road and keep the
car stable and moving forward.
With regard to reactive power, alternating
current power systems rely on
magnetic fields to work. A transformer,
motor, or generator cannot work without
magnetic fields. The principle of operation
of these devices is totally dependent
on those magnetic fields. When reactive
power drops, voltage drops, which can
cause a circuit to fail.
All of these effects can be especially
difficult for system operators to address
during extreme weather events, and
those impacts affect both system reliabilwww.powermag.com
ity
as well as resilience. The Lawrence
Berkeley National Laboratory published
a paper suggesting that resilience has
been a consideration within reliability for
a long time. It credits three recent developments
as drivers for the " unbundling "
of reliability and resilience:
■ Our society's reliance on high-quality,
dependable electrical service has increased.
■
The U.S. has experienced several
high-impact, low-frequency events
(HILF events) with serious effects to
the electric system.
■ New threats are emerging, such as
cyberterrorism and the potential for
geomagnetic disturbances, that could
have devastating effects on the nation's
electric system.
These HILF events, also described
as " Black Sky events, " are at the far
end of the power generation spectrum
(Figure 1)-a complete and lasting disruption
in service.
However, there is evidence that
events historically categorized as lowfrequency
events are now also becoming
more common. The Electric Power
Research Institute (EPRI) found that:
■ Effective load-carrying capability calculations
generally do not consider
weather-correlated deviations from
standard profiles for variable energy
resource (VER) output that might result
in large fleet-wide variations in the
output of both existing resources and
incremental units.
■ The availability and output of renewable
sources being correlated with
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Power June 2023

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