Hill AFB Calendar Year IEEE 1366 Power Reliability Statistics Metric 2015 2016 2017 2018 2019 2020 2021 Unscheduled Outages 43 42 42 21 32 25 12 Customer Minutes 153,027 121,700 88,714 31,058 50,477 70,588 19,530 ASAI 99.9667 99.9736 99.9807 99.9932 99.9890 99.9847 99.9958 SAIDI 174.89 139.09 101.39 35.49 57.69 80.55 21.95 CAIDI 73.36 80.76 60.06 65.52 66.95 49.09 79.39 SAIFI 2.384 1.722 1.688 0.542 0.862 1.641 0.276 Table 1: Power Reliability Statistics for Hill AFB from 2015-2021 Concerning DOD sites, several new microgrid projects are in various stages of development. There will doubtlessly be lessons from the construction and testing of the systems. There are also other smaller examples of tools that can be applied, such as automation and looping. Best practices in the industry reveal proven measures to reduce three significant aspects of an outage. Those aspects are frequency, duration and scope. Each of those measures contributes to reliability differently: 1. Frequency: When a system has less frequent events, the overall annual number of outages is reduced. In the case of Hill AFB, the number decreased from 43 events in 2015 to 12 in 2021. But reducing the number of raw outages alone is just one component of resilience. 2. Duration: Shorter outages translate to less impact on the customer. System automation and improved crew response times reduce outage duration times. 3. Scope: The number of customers impacted by an outage is an important resilience factor. The goal is to limit the extent of the impact from a single event. For example: If five outages affect 10 buildings each, 50 customers lose power. Compare that to three outages of 20 buildings each, where more customers (60) are affected by a lower number of events. An ideal system improvement would reduce all three components of outages. A metric that captures all of those components is “Customer-Minutes Interrupted,” or simply customer-minutes. That customer-minute value is a key component in two reliability indices tracked by the Institute of Electrical and Electronics Engineers (IEEE), the duration index and the availability index. The mission of the power provider is to maximize the availability and minimize outage duration. A perfect system would achieve those goals by applying all available resilience tools, but that comes at a cost. Considering budget pressures, the cost of the resilience tool is almost as important as its availability. Analysis of performance indices and available improvement tools can help power distributors consider key questions about the resilience of their systems. The first question is: “How much reliability is adequate from the customer’s perspective?” The second is “Where should a utility spend its reliability dollars to optimize efficiency and satisfy customers’ electricity requirements at the lowest cost?” The following paragraphs provide an example of investments that balanced those two questions at an Air Force installation in Utah. One example of improved resilience is the electrical distribution system’s performance at Hill Air Force Base, north of Salt Lake City, Utah. The system provides an insightful case study for reducing the number and impact of power outages. In 2015, one year after taking ownership of the system, City Light & Power engineers planned projects and capital investments to renew the electrical distribution system. They introduced automation and other selected tools to reduce the frequency, duration and scope of power outages. The selected investments were based on the classic Asset Management approach. A team determined what they had, assessed conditions and developed a prioritized plan to maintain or replace components that needed improvement. Six years later, the number of outages was down 72%, and the customer downtime from outages was down 87%. While many variables affect the operation of an electrical system, outage, frequency and cumulative duration are most telling. Those two measures speak volumes about the impact of improved system maintenance and investment. Table 1 illustrates the dramatic effects that system investments can make. While there are many uncertainties with power distribution, the table shows a trend of improved system performance over time. 29
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