12 3. DEVELOPING THE PROGRAM PLAN After establishing a potential resiliency program objective, how a resiliency program can support the pursuit of the objective, and how to create a resiliency program, the next step in the Utility Infrastructure Resiliency Playbook (Playbook) is to develop the resiliency program plan. “What gets measured gets done” is the focus of this section, and it details how to develop a resiliency program and effectively measure its impact. An Appropriate Resiliency Metric There are any number of reliability and resiliency measures that are commonly used today to measure performance. These measures can also potentially support the selection of a resilience strategy. As an example, undergrounding is designed to remove entirely exposure to certain types of extreme weather risk. The frequency and severity of risk exposure will dictate if undergrounding is an appropriate strategy. Listed below are a set of traditional and common measures using the promulgated definitions from the Institute of Electrical and Electronics Engineers (IEEE) in their published standard, “P1366 - Guide for Electric Power Distribution Reliability Indices.” In addition, feedback is provided on their applicability to observe or make visible the results of undergrounding strategies. SAIDI (System Average Interruption Duration Index) – Measures reliability as the average accumulated interruption duration per customer during a predefined period of time and is commonly measured in minutes of interruption; It is calculated as Customer Minutes Interrupted (CMI) divided by Customers Served (CS) - Calculating it as a trend over multiple years rather than looking at a single year yields a better understanding of performance. o Undergrounding Applicability: SAIDI is the single most common index used for reliability comparison among utilities. Major outage events dominate the SAIDI calculation because the high number of customers initially out in an outage swamps the number of outage minutes for small groups of customers out of service for lengthy periods as well as accumulated lengthy periods from numerous small outages. Undergrounding strategies impact not only the customers on the circuit section that has been undergrounded it also contributes to quicker restoration of customers experiencing interruptions elsewhere on the system because the avoided interruptions makes the restoration crews available to respond more quickly to other outages. SAIDI is normally calculated system-wide and, if possible, targeting the SAIDI calculation on only the geography where undergrounding strategies are taking place is a better way to measure performance impact. The utility will be expected to demonstrate a SAIDI improvement and if this targeted measure is not possible, another will likely have to be used to demonstrate impact. SAIFI (System Average Interruption Frequency Index) – Measures reliability as the average number of sustained interruptions per customer over a predefined period of time; calculated as Customers Interrupted (CI) divided by Customers Served (CS) - Calculating it as a trend over multiple years rather than looking at a single year yields a better understanding of performance. o Undergrounding Applicability: Frequent short outages associated with main or tap lines will impact a larger number of end customers. The undergrounding of individual home lines and tap lines will typically speed the restoration of power, yet may not necessarily impact the frequency of outage. The
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