Electric Utilities FLISR/Reliability Indices win with 5G and IoT - Part 3

By Ken Caird, Chief Technology Officer, Energy & Utilities at VNCTech Group 

In Part 1 of this blog series we discussed how 5G and the IoT can help utilities save 100’s of thousands of dollars in load reduction with enhancing the capabilities of CVR. In Part 2 we showed how similar dollars values can be save by 5G and the IoT by reducing distribution system losses and efficiencies with enhancing VARVVO capabilities. You can access both Part 1 and Part 2 through this same VNCTech Group BLOG page.


In Part 3, the last of this blog series, we will show how 5G and IoT can help distribution utilities vastly improve reliability indices.


First, let us look how the industry measures reliability. The IEEE Standard 1366 lays out a list 13 indices that can be used to measure reliability. For this blog I am going to focus on two of the most used indices.


1. SAIDI (System Average Interruption Duration Index)

  • The total number of minutes (or hours) of interruption the average customer experiences

  • Formula: SAIDI = Σ (Outage Duration * Number Customers Interrupted) / Total Customers Served)

2. CAIDI (Customer Average Interruption Duration Index)

  • The average time required to restore service

  • Formula: CAIDI = Σ (Outage Duration * Number Customers Interrupted) / Σ (Number of Interruptions * Number of Customers Interrupted)

It is important to clearly understand a few IEEE 1366 definitions:

  1. Customer - “A metered electrical service point for which an active bill account is established at a specific location.”

  2. Interruption - “The total loss of electric power on one or more normally energized conductors to one or more customers connected to the distribution portion of the system.”

  3. Momentary Interruption: “The brief loss of power delivery to one or more customers caused by the opening and closing operation of an interrupting device.”

  4. Sustained Interruption: “Any interruption not classified as a part of a momentary event. That is, any interruption that lasts more than five minutes.” (Note: Some regulators may mandate 1 minute or 2 minutes)

NOTE: Momentary interruptions are NOT included when calculating the indices listed above!

Why are these reliability indices important to electric utilities?

  1. The most important goal is customer satisfaction, the fewer the outages and the shorter the duration the happier the customer. This is especially true in this new world with many people working from home because of Covid-19.

  2. Secondly, state regulators compare utilities against other utilities or national averages. For example, the national average for CAIDI is 1.36 hours and SAIDI is 1.50 hours. Regulators typically set annual reliability indices performance targets on the utilities; Failure to meet these targets, may cause the regulator to implement financial penalties or deny rate increase. Therefore, utilities are usually incentivised to keep their reliability indices close to national averages or better.

As proven by the formulas documented in 1b and 2b above, reliability indices values can be reduced by:

  1. Reducing the duration of the outage

  2. Reducing the number of customers interrupted

  3. Reducing the number of interruptions

Figure 1 is a typical distribution feeder.

Figure 1


In North America feeders are configured in a radial fashion, one source Substation A or Substation B and an open switch at the end of the feeder SW 4. The radial feeder is divided into several “sections” with switches SW 1 through SW 6. Sectionalizing switches allow utilities to sectionalize certain sections of the feeder to isolate this section due to faults or maintenance impacting as few of customers as possible. The normally open switch can then be closed to provide power to those customers down stream of the opened section.

The two major techniques used to improve or reduce reliability indices are tree trimming and automation of the feeder. Automation can often provide a large return on investment. The automation most often deployed is an application called Fault Location Isolation and Service Restoration (FLISR). In an example FLISR program the sectionalizing switches SW 1 – SW 6 are motorized and a relay or Feeder Terminal Unit (FTU) would be installed with each switch. FLISR based software based either centrally on a DMS platform or locally on a substation controller would continually monitor the feeder looking for faults that would cause an interruption. Once an interruption is detected, the FLISR application first opens the sectionalizing switches on either side of the fault. This isolates the fault from the rest of the feeder. The normally open switch is then closed by the FLISR application restoring power to those customers down stream of the fault. If the FLISR application can do this in less time than outage time designated by the regulator (5 min) then the only customers included in the IEEE 1366 reliability indices calculation will be those customers on the faulted section. Therefore, automation can greatly reduce annual reliability indices scores!

To implement FLISR, a reliable, high speed communication system is needed. The FLISR application must be able to communicate with each of the sectionalizing switches and probably some substation IED’s as well. The FLISR application must be able monitor and control all devices on the feeder and substation in order to be able to detect the fault, determine its location, isolate the fault, and restore service to all customers except the faulted section within the defined interruption period (5 min) to ensure that only those customers on the faulted section are included in the indices score.

Timing becomes even more critical if a 1 min interruption limit target is used instead of 5 min. Here, communication speed becomes even more critical.


So, let us look at how 5G can help!

First take a look at why FLISR is not more widely deployed on feeders across North America. There are two main reasons:

  1. Cost of automating the sectionalizing switches (motor operator and FTU/Relay)

  2. Cost of communication infrastructure required for the FLISR app to monitor and control the feeder.


As 5G is more broadly deployed throughout a utilities operating region, the need to purchase and install a dedicated communication infrastructure will disappear. Attempts have been made to use an AMI network for FLISR but these have largely failed because of bandwidth and huge latency issues. 5G is 10 to 100 times faster than typical wireless technologies used today. 5G will allow FLISR to be deployed across a greater number of switches and feeders, while guaranteeing that interruption time targets are not exceeded. Thus IEEE 1366 indices can be greatly reduced if new more stringent targets are introduced.

With 5G with its high bandwidth and low latency (1 – 10 msec) may allow for a new approach to FLISR. That approach is a “transfer trip” scheme. If all devices on the feeder can communicate with each other at high speed and extremely low latency, then the devices themselves can determine where the fault and isolate the fault within milli-seconds. Thus, those customers outside of the faulted section only see a momentary interruption and would not be included in reliability indices calculations. Costly FLISR software may not be needed!

As 5G is rolled out, I expect to see some revolutionary new approaches to improving reliability on electric distribution feeders.


Presently, there is a great opportunity for smaller tech companies to obtain incredible market share if they make the right decisions and invest in this new type of technology leadership. I believe the utility associated tech companies, who embrace dynamic technology leadership to plan and execute the nearby future, will be laying the foundation towards becoming the largest and most successful Company in the industry.

Chief Technology Officer

Energy & Utilities

VNCTech Group



Dallas, Texas, USA

VNC Technologies Company

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