Loss of one Essex 115/34.5 kV transformer may overload the other resulting in load shedding.  This is a Green Mountain Power subsystem issue that was studied as part of the Burlington Waterfront area-specific collaborative, which looked at reliability concerns within the city of Burlington and in northern Chittenden County.

The Burlington Waterfront Area Specific Collaborative ultimately identified a three-phase plan for upgrading the transmission and subtransmission system in the area. Green Mountain Power (GMP), VELCO and Burlington Electric Department (BED), have applied for Section 248 approval in Docket 7314 for Phase I of the identified upgrades. GMP and VELCO recently began preparation to file for Phase II, (also known as the Gorge Area Reinforcement project or GAR), which will involve a new VELCO substation in the vicinity of GMP’s existing Gorge substation.

Although GMP and VELCO will perform an analysis of non-transmission alternatives and conduct public outreach in affected towns, the timing of implementation of VSPC procedures will not allow GMP and VELCO to observe all of the VSPC planning phases for GAR prior to the required filing date for the GAR petition.  Phase III, which is anticipated to be needed in the 2016 timeframe, dependent upon actual load growth, would involve replacement of the Essex transformers. Phase I has been filed for approval and will not be presented to the VSPC for review. Phases II and III will move forward as appropriate, based on the triggers related to load level identified in the area-specific collaborative.

The map below shows roughly the area of Vermont potentially affected by this reliability deficiency.

Loss of the Williston to Tafts Corners 115 kV line, with heavy flows from south to north, would overload the Queen City 115/34.5 kV transformer. The transmission solution examined in the analysis conducted thus far is to install a second 115/34.5 kV transformer at Queen City with requisite substation expansion. An alternative would be to sectionalize the underlying  network. This is primarily a bulk system issue that is the responsibility of VELCO and GMP. These constraints have been addressed by a proposal to automatically sectionalize the 34.5 kV system. Consequently no additional upgrades are needed at this time and no consideration by the VSPC will be required.

The map below roughly the area of Vermont potentially affected by this reliability deficiency.