CUMBERLAND — A proposed new autotransformer at Central Maine Power Co.’s Raven Farm substation have neighbors concerned about noise.
But the electricity provider promises safeguards will be in place to minimize the impact.
The installation, likely to go before the Planning Board next year, is part of CMP’s proposed New England Clean Energy project to deliver hydropower from Canada to the New England grid. It will reduce greenhouse grass emissions each year by 3 million metric tons, according to CMP.
The route of the $950,000 project stretches from Beattie Township in Franklin County, south to Cumberland’s substation at 37 Greely Road, CMP spokesman John Carroll said during a neighborhood meeting July 26. CMP received Planning Board approval to build the substation in 2011.
“As a single project, it’s a phenomenal input to a collective problem around climate change,” Carroll said.
Although all the power is being sent to Massachusetts, Maine benefits include job creation during the six-year permitting and construction process, $18 million in added tax revenue each year for the host communities, and annual savings of $40 million-$45 million in future energy costs, according to CMP.
Although no transmission lines will run to Raven Farm, the transformer is “a large and important component of the system,” Carroll said, adding that “probably the most notable aspect of them, from a community perspective, is they can make noise.”
CMP has had difficulties in other communities with substations that “turned out not to be good neighbors,” he said, but “when we looked at what we were going to do here in Cumberland, we said we really need to be a good neighbor. And we need to make sure that this substation is going to meet the expectations not just of your ordinances and your legal requirements, but the expectations of the neighbors.”
Gabe Weger, a sound engineer on the project, noted that the vibrations caused by the transformer cause a low-frequency hum. CMP has chosen a low-noise unit that is “specifically much quieter than existing transformers at some of the other sites,” Weger said.
The device is capped at an average of 65 A-weighted decibels (dBA) around the outside of the unit, and a sound wall is to be installed on all four sides, to limit noise.
“Unweighted decibels would be the same in the low frequencies, same in the high frequencies,” Weger explained. “The A-weighting scale takes down those lower and higher frequencies because you generally don’t hear them. It emphasizes the middle frequencies.”
The transformer was originally designed to produce a peak sound of 45 dBA at the property line, which would meet Maine Department of Environmental Protection regulations, Weger said.
“A lot of you said that wasn’t good enough, and that you wanted to go lower than that,” he said, referring to meetings held with neighbors in recent months.
The 15-foot transformer would now be 10 dBA quieter, surrounded by a 20-foot steel sound wall that is taller than the unit. The wall, filled with material that absorbs sound, could cut sound emanation by 5-15 decibels, Weger said.
According to a computer-generated model of sound levels around the site in worst-case scenarios, if the transformer is installed, an average of 20 would be heard at the property line – typically, the lowest threshold of hearing, Weger noted. An office generates about 50, and a farm field with a light breeze and birds chirping is about 40, with nighttime sound levels closer to 30, he added.
Resident Curtis Ingraham asked CMP to provide specifications for the unit once they are available. Neighbors among the roughly 20 in attendance, concerned about noise impacts from the transformer, asked CMP officials to better advise them in advance of future community meetings.
Noise mitigation is one of the conditions the Planning Board imposes, Town Manager Bill Shane told CMP officials.
“One of the conditions will be that we measure, after the installation, the decibel level that matches these diagrams, and that will be a condition that you have to meet,” he said. “You’re modeling this, and you’re basically asking us to take this on good faith, but we need to see the performance at the end, regardless of what you give me for a spec sheet.”
John Carroll, spokesman for Central Maine Power, discusses a proposed new autotransformer at the company’s Raven Farm Substation in Cumberland at a neighborhood meeting July 26.The autotransformer project at 37 Greely Road in Cumberland, likely to go before the town’s Planning Board next year, is part of CMP’s proposed New England Clean Energy project.