Robert Shelley, the distribution and engineering manager for the municipal utility, presented a report on improving reliability to BLP trustees on June 27.
The BLP’s unadjusted rating for the average length of power interruption is twice the national unadjusted average at 208.56 minutes. The BLP averages 2.08 unadjusted interruptions per year, while the national average is one interruption. Average BLP outages last 100.14 minutes, while the national average is 86.1 minutes.
These numbers include major weather events, Shelley explained, such as an ice storm that caused an outage in April 2018. Abnormal events such as tornados and 100-mph winds that would cause widespread outages are commonly not counted toward other utilities’ reliability averages, Shelley said, but using unadjusted figures helps highlight weaknesses and improve the planning process.
“If we do that, our numbers look better than we actually perform,” he said. “They’re not realistic.”
There are three tiers for system performance ratings: normal, wherein all substations and distribution circuits are in service; and two contingency stages, which entails either a single transformer or circuit breaker out of service, or two or more.
The BLP’s substations run at 40 percent normal rating, 80 percent first contingency, and never dip into second contingency of two or more outages. Distribution equipment runs at 50 percent normal rating, and is at 90 percent loading through first contingency. Power availability is also a tick under the adjusted national average – 99.96 percent (the ideal rating is 99.99 percent).
Voltage remains a problem for the utility on older, small sections of the system that overload at peak times, Shelley explained, which causes the voltage to dip under the heavy load. Normal levels are at 5 percent, with contingency levels at 10 percent. These sections are scheduled to be rebuilt and replaced in the next two years, BLP officials said.
Twenty percent of outages are caused by trees, while another 20 percent are never determined. Fifteen percent are caused by animals, typically squirrels, while 6 percent are weather related.
Two substation outages last year occurred on July 4 and Sept. 21.
BLP General Manager Dave Walters said the utility’s ability to produce energy locally does not factor into reliability. Outages occur on the distribution side, he said, such as power lines, and not from a lack of energy supply.
“None of them were caused or saved by us having local generation,” Walters said. “Local (energy production) does not impact this reliability analysis one bit.”
Walters said the report will drive future projects for the utility. Most recently, the BLP completed a three-year transmission rebuild that expanded access to the regional transmission grid. The equipment is expected to last 30-50 years.
Shelley said tree clearance has been improved in recent years. The report will be updated regularly in the future to track progress, he said.