On the subtransmission system, several potential reliability issues were also identified. The reliability of the subtransmission system can be improved by reinforcements made on the transmission system system and vice versa; therefore, many of the subtransmission issues may be resolved by implementation of transmission solutions, and subtransmission fixes may sometimes resolve transmission system issues. The table in Figure 3-2 shows the reliability issues that would remain unresolved after implementation of the proposed transmission solutions shown in Figure 3-4. The table shows which part of the electric system is causing the reliability issue, i.e., transmission, subtransmission, or the failure of a transformer within a substation. The reliability impact of the equipment failure (or “contingency”) is shown as either causing high or low voltage, or as a thermal issue in which equipment exceeds its rated temperature.

The table illustrates that there are five general subtransmission areas with potential reliability issues including Ascutney, Chelsea, Montpelier, Rutland, and St. Albans. At the subtransmission level there can be more flexibility concerning the reliability level to which the system is designed when compared to the transmission system because the subtransmission system is not currently subject to mandatory federal reliability standards. For example, it may be acceptable in the area to incur an infrequent power outage rather than to invest in infrastructure to eliminate the power outage risk. The affected utilities will determine what, if any, projects are required to address the potential reliability issues on the subtransmission system. The affected utilities have not yet submitted these evaluations.

Figure 3‑2. Subtransmission potential reliability issues grouped by location (assuming proposed transmission projects are completed). 

Location	Year Needed	"90/10" Load Forecast for Year	Contingency	Issue	VELCO Criteria Violations	Affected DUs	Lead DU
Ascutney	2009	1141 MW	Subtransmission	Voltage	Low voltage & voltage collapse	CVPS	CVPS
Ascutney	2010	1155 MW	Transfomer	Thermal	Ascutney-Lafayette	CVPS	CVPS
Ascutney	2009	1141 MW	Transfomer	Thermal	North Springfield-Riverside	CVPS	CVPS
Ascutney	2009	1141 MW	Transfomer	Voltage	Ascutney	CVPS	CVPS
Ascutney	2009	1141 MW	Transmission	Voltage	Ascutney	CVPS, GMP, Ludlow	CVPS
Ascutney/ Cold River	2009	1141 MW	Transmission	Thermal	Wallingford-Cavendish	CVPS, Ludlow	CVPS
Chelsea	2009	1141 MW	Transmission	Voltage	Chelsea	CVPS, WEC	CVPS
Chelsea/ Hartford	2013	1185 MW	Subtransmission	Voltage	Chelsea-Hartford	CVPS, GMP, WEC	CVPS
Montpelier	2009	1141 MW	Subtransmission	Thermal	Berlin to Mountain View Tap to Montpelier	GMP, WEC	GMP
Montpelier	2009	1141 MW	Transfomer	Thermal	Berlin-Mnt View-Montpelier	GMP, WEC	GMP
Montpelier	2016	1215 MW	Transmission	Thermal	Berlin-Mountain View Tap-Montpelier	GMP, WEC	GMP
Rutland	2009	1141 MW	Subtransmission	Thermal	North Rutland to East Rutland to South Rutland	CVPS	CVPS
Rutland	2009	1141 MW	Transfomer	Thermal	North Rutland-South Rutland	CVPS	CVPS
Rutland/ Cold River	2009	1141 MW	Subtransmission	Voltage	Rutland-Cold River	CVPS	CVPS
St Albans	2009	1141 MW	Subtransmission	Thermal	Fairfax Falls to Milton	CVPS	CVPS
St Albans	2009	1141 MW	Subtransmission	Thermal	North St Albans to Nat Carbide	CVPS	CVPS
CVPS = Central Vermont Public Service, GMP = Green Mountain Power, WEC = Washington Electric Co-o

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