Abstract
This report documents a magnetic field study completed by POWER Engineers, Inc. (POWER) for Mayflower Wind Energy, LLC (Mayflower). The study examines eight (8) cable configurations associated with the portions of the Mayflower Wind project in the Rhode Island and Massachusetts jurisdictions, both offshore in state waters and onshore on Aquidneck Island and Brayton Point. These configurations are listed below and described in the Cable Installation Scenarios section. Preliminary cable sizes and drawings of the circuit configurations are located in Appendix A and Appendix B.
- HVDC offshore, bundled configuration, 6.6 ft (2.0 m) burial depth.
- HVDC offshore, bundled, on seafloor under a 1.0 ft (0.3 m) thick concrete mattress.
- HVDC offshore, non-bundled, cables separated by 164 ft (50 m), 6.6 ft (2.0 m) burial depth.
- HVDC landfall horizontal directional drills (HDD), beach case under Island Park Beach near Boyd’s Lane and Park Avenue. Cable depths are 25 ft (7.6 m) and 40 ft (12.2 m) below the surface with a 15 ft (4.6 m) horizontal separation.
- HVDC onshore, single circuit duct bank, 3.2 ft (0.96 m) burial depth.
- HVDC onshore, double circuit duct bank, 3.3 ft (1.01 m) burial depth.
- HVDC onshore, alternate double circuit duct bank, 3.4 ft (1.03 m) burial depth.
- HVAC onshore, single circuit duct bank (two cables per phase), 3.3 ft (1.01 m) burial depth.
POWER has calculated magnetic field in milligauss (mG) for the above configurations. Interpretation of results and comparison to industry limits will be performed by others. Human exposure to electric fields is negligible when a cable includes a grounded sheath and/or armor. This is the case for the Mayflower wind project. Therefore, calculation of the small external electric fields due to voltages induced on cable sheaths and/or armor is not included in the study.