NSTAR adds generators in place of failed undersea cable

NSTAR has placed temporary generators at the Oak Bluffs highway garage to help meet power demands this summer. — Photo by Ralph Stewart

On Friday afternoon, one of four submarine NSTAR power cables from Falmouth to Martha’s Vineyard failed, causing brief power outages across the Island. Another cable is permanently out of service and due to be replaced.

With two of the Vineyard’s four electrical umbilical cords out, NSTAR has beefed up its ability to generate power to meet increased summer demand, NSTAR spokesman Mike Durand told The Times on Tuesday.

NSTAR currently maintains five permanent diesel generators to supplement power provided by cable. In anticipation of increased demand, the utility transported eight temporary generators to the Island before the start of the summer. “We have since added seven as a result of this cable failure,” Mr. Durand said.

The generators will run as needed and are connected to different distribution lines. “That is done strategically based on what we anticipate the demand in a particular part of the Island will be,” he said.

Mr. Durand said providing power to the Vineyard is a multi-faceted effort. It is not simply a matter of flipping a switch, he said.

“Being an island it does take engineering that the mainland does not require and part of that is anticipating issues and the need for additional generation,” he said.

Two cables cross Vineyard Sound and land on shore at West Chop in Tisbury. Two other cables land at Eastville in Oak Bluffs.

NSTAR is currently in the process of installing an approximately 4.5-mile long hybrid fiber optic and electric cable across the sound. New utility poles that have generated considerable controversy will carry the new line.

NSTAR is also making plans to repair the cable that failed on Friday. How soon that will happen will depend on the ability to coordinate repair crews and a barge. The location of the fault is in the shipping channel and the cable must be lifted to the surface. “There is a lot of coordination that needs to be done,” Mr. Durand said.

A Martha’s Vineyard Commission staff report prepared in January 2013 said total installed power capacity to Martha’s Vineyard is 55 megawatts of electricity (MWe), assuming all sources operate. A failure of the main cable, known as cable 99, would reduce installed capacity to 38 MWe, the report said.

In July of 2012, a peak of 55.4 MWe was achieved. Load forecasts project peak load climbing to 73 MWe by 2022, according to the report.