IEEE PES T&D Conference & Exposition 2022 - 118

and provide the highest standards of electricity to all customers.
This article explains a possible path forward.
Moving Beyond Average
Reliability Metrics
For most anyone, electric reliability is a familiar, and likely
feared, subject. We associate it with internet outages and cold
showers, or more gravely, with environmental disasters and
emergency events. Despite our around-the-clock dependence
on electricity, power system reliability is not necessarily targeted
at customer needs. This is because the metrics used by
regulators and utilities to measure electric reliability are outdated
and were limited by technology to be based around the
utilities'-rather than customers'-perspective of reliability.
While core reliability metrics have not changed substantially
since the 1960s and '70s, the need for new metrics is
now coming to a head, as the electric grid experiences key
changes in how electricity is both generated and used. As
people become more reliant on electricity for digital services
and transportation, the importance of reliability is growing,
and these customers increasingly expect zero interruptions.
This was highlighted during the COVID-19 pandemic as
people who are sheltering and working from home relied on
always-available electricity supplies.
There are also new classes of customers, such as distributed
generation owners, energy storage owners, and aggregators,
each of which has unique requirements related to
grid reliability. Despite many improvements already made
to accommodate modern energy systems, such as distribution
automation and investment in smart grid technologies,
customer satisfaction is on the decline.
The disconnect often occurs between common systemwide
performance metrics such as SAIDI, SAIFI, and MAIFI, and
the performance experienced by individual customers. When
power sector investments and incentives are based solely on
these decades-old metrics, utilities are encouraged to focus on
improving their whole system average performance rather than
addressing the needs of their worst-served customers at the
grid edge. For example, although electricity customers depend
on system resilience during storms, standard reliability metrics
often exclude days with major resilience events. Ironically, this
is when homes and businesses are most impacted by outages.
To develop a more complete picture of utilities' reliability
performance for their customers, it is important to both consider
a broader range of metrics and to use existing metrics
differently. Fortunately, we have examples from around the
world of enhanced metrics and best practices for reliability
reporting that create a more customer-oriented perspective of
utilities' performance. These examples are reviewed in this
article and can help set a new direction that drives investment
in all-around reliability and customer satisfaction.
We first explain the history of reliability metrics and how the
industry landscape is changing in ways that affect the appropriate
metrics and how they are used. This is followed by key
steps and best practices that utilities can follow to create a more
118
ieee power & energy magazine
balanced approach to reliability that aligns with the degree of
electric reliability that customers need and expect. Finally, we
describe upcoming technologies that can strengthen grid reliability
alongside modern customer-centric metrics.
History of Electricity Reliability Metrics
As electricity expanded around the world, power system
stakeholders began to undertake grid reliability assessments to
understand the causes of outages on their distribution grids. A
quick history of reliability tracking is shown in Figure 1.
Since the 1940s, utilities have reviewed their system performance.
Starting with simple surveys to identify failure
rates and causes, the utility industry has developed sophisticated
tools and indices to calculate system performance and
reliability. In the late 1960s and early 1970s, utilities developed
and utilized standard metrics that are still commonly
used today, including SAIFI, SAIDI, and MAIFI.
While these metrics look at overall system performance,
it is important to note that they often exclude major reliability
event days. This provides utilities with a better view
of their day-to-day reliability, but by excluding major event
days, these same metrics can hide issues related to overall
system resilience. The utility industry has seen some updates
and new metric development since the 1970s. Most notable
is an increased tendency to focus on issues at the edge of
the grid and prioritize customer-oriented operation. But the
original metrics of the 1970s remain the most commonly
used tools of measurement in the industry.
Customer-focused metrics originated in the early 2000s.
One such metric, the Customer Average Interruption Duration
Index (CAIDI), has historically been a popular metric
with utilities and regulators because of its perceived focus on
customer experience, but it is increasingly viewed as a problematic
measurement. This particular metric simply measures
the ratio of outage frequency to duration. In his 2009 " Electric
Power Distribution Reliability, " Richard E, Brown noted that
" reliability could be improving in both frequency and duration
[SAIFI and SAIDI improving], but CAIDI could be increasing
[appearing worse than before. " For example, investment in
technologies such as distribution automation or lateral protection
can lead to significant SAIFI and SAIDI improvements
and improve the reliability experienced by customers. But, if
SAIFI improves more rapidly than SAIDI, CAIDI will still
increase, giving a false impression of worsening performance.
Since the beginning of the new millennium, the utility
industry has seen two key developments in the progression of
performance metrics. First, new rules have been established
for identifying and separating major event days from dayto-day
performance measurement. Second, the industry
has introduced two measures for the customer experience
that look at both cumulative and individual outage impacts
for customers. Some regulators are now including the use
of CELID and CEMI in their reporting requirements to
capture long interruption durations and multiple interruptions,
respectively.
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