3. Project Descriptions

The following project descriptions are based on testimony presented by SDG&E.⁶ In addition, SDG&E provided to the Commission numerous documents describing the projects in greater detail under the protective order adopted in this proceeding.

3.1 Miguel-Mission Project

Miguel is an entry point for electrical power from east and south into the SDG&E load center, which is north of Miguel. It is also an entry point of Mexico power for CAISO imports into other service territories north of SDG&E, i.e., SCE and PG&E. Power entering from Miguel can potentially originate from Mexico and the US-Mexico border area, from Arizona via the Southwest Power Link (SWPL), and from the Imperial Irrigation District. At the current time, most of the power enters Miguel via SWPL.

The proposed Miguel - Mission Project is designed to relieve potential overloads on various 69 kV and 138 kV transmission lines and 230/69 kV and 230/138 kV transformers on SDG&E's system. These potential overloads would occur during high power imports from Mexico and interconnection of new merchant generators in the US-Mexico border region. Figure 1 presents a map with the locations of these generators.

Without this project, SDG&E /CAISO imports are constrained and the CAISO must utilize congestion management to reduce generation output during high imports to prevent overloads to maintain reliability. The Miguel-Mission Project would relieve this congestion by allowing an additional 560 MWs to move north of Miguel.

FIGURE 1

The proposed Miguel-Mission 230 kV line will have two sections: Miguel-Fanita Junction (approximately 24.5 miles) and Fanita Junction-Mission (approximately 10 miles). For the first section, SDG&E proposes to modify existing 138 kV steel lattice towers from Miguel to Fanita Junction to accommodate a new 230 kV circuit with four 336 thousand circular mil (kcmil) conductors per phase. SDG&E will relocate the existing 138 kV and 69 kV transmission circuits that occupy these 138 kV steel lattice towers to a new wood/steel pole line. For the Fanita Junction to Mission section, the current 230 kV structure that has a split-phase one circuit will be changed into two circuits, both reconductored with two 900 kcmil conductors per phase. All construction is planned to occur within existing SDG&E right-of-way.

SDG&E presents a preliminary estimate of $26 million in project costs (in 2004 dollars) with a tentative in-service date of June 2004, subject to any Commission licensing requirements. SDG&E's planning studies looked at the upgrades of various lines and transformers at Miguel and upgrades of 69 kV and 138 kV lines west of Miguel. However, SDG&E states that these alternatives were all more costly than the proposed Miguel-Mission project, and were therefore not considered further in the economic analysis.

3.2 Imperial Valley Project

The Imperial Valley Project is also designed to address transmission congestion problems as new generation comes on line. SDG&E's studies show that the single existing 500/230 kV bank at Imperial Valley will overload with all lines in service with high export from Mexico and with generation interconnection at Imperial Valley. (See Figure 1.) In addition, the bank also overloads under the loss of the Tijuana - Miguel 230 kV path or the double contingency of the Miguel - Mission and Miguel - Sycamore 230 kV lines. Without a transmission system upgrade to the Imperial Valley bank, congestion management would be used to curtail generation and maintain reliability.

SDG&E proposes to replace the existing transformer with a 500/230 kV, 1120 megavolt-ampere (MVA) transformer bank and install a second transformer of that same capacity within the boundaries of the existing substation. These upgrades are expected to more than double the approximately 500 MVA that can currently move through the Imperial Valley substation. However, as discussed further below, without the Mission Miguel Project, these modifications will not provide additional power to SDG&E's load center. The earliest feasible in-service date for the modifications is June 1, 2003. The total project cost is estimated to be $29.4 million in 2003 dollars.