VELCO’s LRTP and Central Vermont Public Service (CVPS) have identified several reliability deficiencies in the Southern Loop Study area. At the VELCO system level, they include potential loss of the 345/115 kV transformer at Vermont Yankee, which affects parts of New Hampshire, as well as Vermont. At the distribution utility, subsystem level, deficiencies in CVPS’s system are associated with 46kV line contingencies between Bennington and Brattleboro, loss of 115/46 kV and 115/69 kV transformers into Bennington or Brattleboro at Woodford Road and Vernon Road, and loss of the N186, which has the same impacts as loss of transformers at Vernon Road.  These impacts are localized to the 46 kV and 69 kV subsystem load between Brattleboro and Bennington.

Detailed NTA analysis for the Southern Loop Study Area was completed in September 2007 for the bulk system issues and in December 2006 for CVPS issues. Following extensive public involvement processes, VELCO and CVPS completed solution selection, for both bulk and subsystem deficiencies, and filed for Section 248 approval with the PSB in November 2007. The Board has opened Docket 7373 to consider the Southern Loop 248 petition.

VELCO’s studies found that loss of the Vermont Yankee to Coolidge 345 kV line (the “340 line”) can have adverse impacts on significant portions of Vermont as well as portions of New York and New Hampshire. These adverse impacts can include overloaded transmission facilities, unacceptably low voltage and/or voltage/system collapse. (See map below left.)

The proposal submitted to the Board in Docket 7373 includes a combination of upgrades required to solve the existing subsystem deficiencies, as well as the line known as the Coolidge Connector to solve regional reliability problems and to provide a new source to Brattleboro and the Southern Loop. The Coolidge Connector line is needed now, but likely cannot be completed until 2011.

Although NTA solutions were determined not to be a feasible way to avoid or defer the Coolidge Connector, CVPS has asked the VSPC Technical Coordinating Subcommittee to form a project study group to consider implementing additional demand response that may increase system reliability before the line can be placed in service. Action on the recommendation will be taken by the VSPC at or before its next meeting, March 11, 2008.

The three maps below show roughly the areas of the state that are vulnerable based on the reliability deficiencies described above.