One of the five GE Haliade 6MW turbines turbine remains offline at the first offshore wind project in the Americas.
The remainder of the project, in the Atlantic Ocean, off the US's Rhode Island, has completed testing and is expected to be online within days.
"As a result of human error a drill bit left inside the generator of turbine number two caused some damage," said a Deepwater spokeswoman.
"GE will repair the turbine and expects to have it operational in the near term," she added, in a written statement.
According to the local ecoRI newsletter, a 15cm drill bit was left behind, during assembly, between the turbine's generator and direct-drive system. Magnets in the generator were damaged.
The spokeswoman declined to answer when asked if commissioning of all five GE Haliade turbines would occur this month, as originally planned by Deepwater.
Deepwater Wind president Chris Van Beek told the newsletter that the repair is covered under a warranty with GE.
"This short delay for this turbine is not unusual," said the spokeswoman.