Wildlife near power equipment is the most common cause of outages at public power utilities, and the failure of overhead equipment is the second most common cause, according to the American Public Power Association's latest annual survey on distribution system reliability. Weather was third on the list, while vegetation was fourth.
"The clear implication is that preventative system maintenance programs can be a valuable tool to reduce outages," said the report, Evaluation of Data Submitted in APPA's 2015 Distribution System Reliability and Operations Survey.
Data presented in the report are based on APPA's 2015 Distribution System Reliability and Operations Survey. The data reflect activity from Jan. 1, 2014 to Dec. 31, 2014. In all, 112 utilities from nine APPA regions took part in the survey.
Use of squirrel guards is common
Ninety-three survey respondents reported that they have a vegetation management/tree trimming program, while 86 reported that they use squirrel guards. In many regions, wildlife-related outages are due to squirrels, the report noted.
"Since a utility pole is similar to a tree, squirrels frequently climb poles," the report said. "The heat emitted by electric lines can attract a squirrel, particularly during cold weather."
Routine distribution inspection and maintenance programs were reported by 74 utilities; thermographic circuit inspections were reported by 68 utilities; lightening arrestors were used by 53 utilities; and 46 utilities reported that they had converted overhead lines to underground ones.
Utilities used different methods to track outage data, the survey found.
Fifty-seven of the 112 survey respondents reported that they used APPA's eReliability Tracker software to keep track of outages, while 49 used a supervisory control and data acquisition, or SCADA system. Responders also reported using database records, spreadsheets and outage management systems. A relatively small number of survey respondents reported that they used smart grid, smart meters or automated metering infrastructure to track outages.
Ninety-one utilities said they applied reliability indices system-wide, while 66 applied such indices by feeder/circuit, and 40 did so at the substation level.
Sustained outages are the most commonly tracked outage type, the report said.
Utilities were asked for outage reliability statistics in the form of System Average Interruption Frequency Index, or SAIFI; System Average Interruption Duration Index, or SAIDI; as well as Customer Average Interruption Duration Index and Average System Availability Index.
Among the other topics covered by the report are momentary outages; power quality; and workforce issues, including average customer-weighted rate for employing journeyman, apprentice and contracted lineworkers. The survey also asked public power utilities about the number of lineworkers per square mile.
The survey also asked questions about details on system operations — for example, the types of breakers used in utility substations; transformer maintenance practices; the kinds of materials used for primary feeder cables; types of fault indicators; and average and median distribution system peak load.
This year, APPA added a new section to the survey on construction design, intended to help illustrate how utilities handle easements and codes, and how they serve new construction.
To measure system reliability successfully, "utility staff should commit to the long-term uninterrupted collection of reliability related data," the report said, adding that measuring reliability "is a deliberate process and takes a significant number of observations before it yields meaningful data."
The data used in the survey "represent a multitude of different takes on distribution systems and reliability," the report concluded, adding that APPA believes the survey provides valuable benchmarking information to its members about the operation of distribution systems across the public power sector."
"This report shows how important it is to work together as an industry to benchmark reliability and operations data," said Alex Hofmann, director of energy and environmental services for APPA.