IEEE Power & Energy Magazine - September/October 2021 - 68

New methodologies and tools are needed to improve power
system resilience to extreme, HILP-type events, but their practical
implementation is still in its infancy.
This has become evident in the power system of the National
Electricity Market (NEM), a long, interconnected grid serving
southeast Australia. The NEM grid is leading the world in the
installed capacity of VRE sources and DER integration. In
recent years, it has also experienced several extreme events,
such as the severe storm system that led to the South Australia
" black system " event of September 2016, where a major part
of the NEM power system was disconnected for several hours.
New methodologies and tools are needed to improve
power system resilience to extreme, HILP-type events, but
their practical implementation is still in its infancy. This
includes developing suitable regulatory frameworks to support
adequate planning, operational mechanisms, and solutions.
It also requires effectively assessing the full costs
associated with both the consequence of these events and
the mechanisms needed to manage them.
In this article, we present pioneering work developed in
the context of the 2019 report, " Review of the South Australian
Black System Event, " that took place on 28 September
2016. The work was undertaken by the Australian Energy
Market Commission (AEMC) and supported by the Melbourne
Energy Institute at the University of Melbourne.
This report covered technical and regulatory aspects aimed
at evolving existing grid planning and operational frameworks
to help address emerging challenges of integrating
more inverter-based resources while facing severe weather
events driven by climate change.
We specifically discuss how low-carbon grids evolving
power system risks, uncertainties, and resilience profiles are
increasingly threatened by so-called indistinct events. These
are distributed and inherently uncertain events that act across
multiple generation and network assets in an affected area over
time. From a regulatory perspective, we discuss some of the
issues that decision makers, including policy makers, regulators,
and system operators, may face when making decisions to
enhance resilience under conditions of uncertainty. We explore
potential regulatory framework approaches to improve resilience
at the lowest cost for consumers. Finally, we put forward
some recommendations for how system operators might procure
solutions to take advantage of new technologies to enhance
power system resilience in low-carbon grids. We include practical
examples from what has been proposed in Australia.
Security and Resilience of
Low-Carbon Grids
Low-carbon grids based on VRE, DERs, and inverter-based
resources face pressing operational challenges in terms of
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maintaining system security. In Australia, the South Australia
" black system " event in 2016 prompted important questions
and calls for urgent measures to improve the NEM power
system's security as advocated by the 2017 Finkel Review of
the NEM, led by the Chief Scientist of Australia Alan Finkel.
Besides enhancing the security of the power system, a
crucial focus is on improving the power system's resilience
to extreme events. While security is the operational component
of reliability historically associated with the system's
ability to respond to credible contingencies, resilience
explores how power systems deal with rarer, more severe
noncredible contingencies (e.g., simultaneous loss of multiple
system components) associated with HILP events. For
example, the IEEE Power & Energy Society Task Force on
Definition and Quantification of Resilience defines resilience
as " the ability to withstand and reduce the magnitude
and/or duration of disruptive events, which includes
the capability to anticipate, absorb, adapt to, and/or rapidly
recover from such an event. "
For grids dominated by inverter-based resources, VRE
technologies, and DERs, the increasing fragility of the system
makes cascading outages more likely. In a low-carbon grid,
security and resilience become more intertwined. Interesting
examples refer to the assessment of frequency response and
operating reserves to deal with " indistinct " events, which are
intrinsically highly uncertain.
The more uncertain and variable operating profiles
of low-carbon grids prompt our need to consciously and
actively think about resilience. Many power systems have
historically operated with classical N−1 or N−2 security criteria
that ensure the system can keep supplying customers
safely even after the loss of one or two major components.
On the other hand, extreme events where multiple assets can
fail due to cascading may be classified as N−X, with X much
greater than two. It is not possible to economically run a
power system to realize secure operation against such N−X
contingencies and thus also provide resilience. New operational
and planning approaches are therefore needed, as discussed
later in this article for the Australian case.
The Power System Security Arrangements
for Managing Risk to Its Operation
Power system security is concerned with managing the risk
that a contingency event could pose to satisfactorily operating
the grid with frequency, voltage, current, and plant operation
within appropriate standards or ratings. Consequences
include the risk of a cascading outage of power system
september/october 2021
IEEE Power & Energy Magazine - September/October 2021

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