Refer to Table ZS-1 and Figure ZS-9

Summary of key findings

• Low voltages throughout Zone 3 require a total of 245 MVAR of capacitor banks be installed by 2010.
• A significant number of lines and substation terminals will be uprated to avoid overloads under single contingency.
• Maintaining reliability of service to load in and around the Madison area requires that system reinforcements be implemented in the near term. Longer term, a 345-kV source on the west side of Madison will be required.
• Load growth in Rock and Walworth counties, higher than the ATC average, is driving the need for several system reinforcements in these counties.
• Import capability from Illinois can be severely limited by transmission facilities outside of our system for loss of the Wempletown-Paddock 345-kV line (ATC/Commonwealth Edison facility). This limitation has been addressed to some degree by installing a second 345-kV line between Wempletown and south central Wisconsin (Paddock Substation). The underlying 138-kV transmission system in the Janesville area and to the north still poses limitations for transfers into the Madison area.

Import capability from the areas to the south and southwest of Zone 3 has been a major concern. To help address this, ATC proposed the first transmission project within the Midwest Independent System Operator (MISO) footprint driven by economics. This project, the Paddock-Rockdale 345-kV transmission line, significantly reduces congestion and enhances import capability into Zone 3 and ATC as a whole.

ATC received approval May 30, 2008, from the Public Service Commission of Wisconsin to construct this additional circuit primarily on an existing transmission line corridor between the Paddock Substation in the town of Beloit and the Rockdale Substation in the town of Christiana. (approximately 35 miles).

This project benefits electric consumers differently from other electric transmission projects that ATC has proposed in recent years, which largely have been in response to weaknesses on the system and related reliability issues. The primary purpose of a high-voltage transmission line to the south is to give local distribution utilities improved access to lower cost power from other areas in the region and bring it into Wisconsin. While this project is largely driven by economics, it also benefits electric consumers with a stronger, more stable electric system.

Wisconsin has limited transmission line connections to other states compared to its neighboring states. This limits the ability of electric utilities to access wind energy or sources of lower-cost electricity from other regions.

ATC submitted a construction application to the PSC in the spring of 2007 outlining its proposal and seeking regulatory approval. The route the PSC approved was ATC's designated preferred (recommended) route along an existing utility corridor where a 345-kilovolt line is located. A second route alternative along another utility corridor approximately two miles east of the approved route was rejected by the PSC.

In response to low voltages throughout Zone 3, a total of 245 MVAR of capacitor banks distributed at the Sheepskin, Richland Center, Brewer, Beaver Dam, Kilbourn, Artesian, Lamar, Union Townline, Dickinson, and Spring Green substations were deemed to be the most feasible solutions in the 2009-2010 timeframe. In 2009, 182 MVAR of reactive compensation was installed. The remaining 63 MVAR will be in service (Sheepskin, Lamar and Spring Green) in 2010.

We currently mitigate several of the identified 138-kV low voltages through remote control of the 138/69-kV transformers in the affected areas. In certain instances, transformer load tap changers are adjusted to bring the 138-kV contingency voltages above the planning criteria limits while maintaining the 69-kV bus voltages above criteria limits. This is a balancing act, and as loads continue to grow the process will no longer be effective.

There were a number of facility overloads and several facilities near their emergency ratings in Zone 3 based on the 2010 analysis. Many projects are either planned or proposed to address these near-term thermal problems by 2010. As a result, we propose to uprate three 69-kV lines and two 69-kV substation terminals.

Overloads for outages of the Dane-Waunakee, Blount-Ruskin or West Middleton-Pheasant Branch 69-kV lines or the North Madison 138/69-kV transformer highlight the need for additional transmission reinforcements in this area. The first phase of the reinforcements is complete. This included uprating the Dane-Waunakee, Waunakee-Huiskamp and West Middleton-Pheasant Branch 69-kV lines as well as uprating the North Madison 138/69-kV transformer. The second phase of the reinforcements includes the construction of a new 138-kV line, North Madison-Huiskamp, and the construction of a new substation with a 138/69-kV transformer near Huiskamp, which was completed in 2009.

Several pending overloads and low voltages in southern Dane and Green counties are prompting the need for additional transmission system support in the area. The existing 69-kV line between Oregon and Verona substations will be rebuilt on new structures with larger conductor in part because of its deteriorated condition. This rebuild will help relieve some of the voltage and loading problems in the near term. In addition, a new 138-kV line from the Fitchburg area (Oak Ridge Substation) to Verona (previously Montrose Substation) is being planned to provide additional support that is needed as loads continue to grow in southern Dane County at a rate of twice the ATC system average. The Montrose endpoint was changed to the existing Verona Substation due to routing issues, public input and the Oregon-Verona rebuild plan.

The western portion of Jefferson County and the eastern portion of Dane County have also experienced high residential, commercial, and industrial load growth. Much of the area is served by the Rockdale Substation. Studies conducted by Planning indicate that by 2009, unacceptable voltages could be experienced in the Academy, Boxelder, London, Cambridge, Lakehead, and Jefferson substation areas with the outage of any segment of the Rockdale-Boxelder or Rockdale-Jefferson 138-kV lines. In order to provide reliable service to the area, a new Jefferson-Lake Mills-Stony Brook 138-kV line has been planned.

There are several pockets of low voltages and some overloads in eastern Rock and western Walworth counties. The recently completed maintenance rebuild of the Turtle-West Darien 69-kV line with initial operation at 69 kV remedies this situation. In conjunction with this project, a new line from West Darien through a new Southwest Delavan Substation to the Delavan area is planned. This project allows ATC to retire a portion of the existing Turtle-Bristol line, which is routed through an environmentally sensitive area, and to provide service to requested transmission-to-distribution interconnections (Southwest Delavan and North Shore substations).

Walworth County will require additional support to accommodate transmission-to-distribution interconnections, mitigate impending overloads on various facilities and support voltages at numerous substations under contingency. The conversion of the Rock River-Elkhorn line from 69-kV to 138 kV was recently completed to resolve these issues. The 138-kV Rock River to Elkhorn line conversion project will not only address thermal overloads but also make the system ready for rebuilding both Colley Road to Brick Church 138- and 69-kV lines. These two lines have condition issues that require they be rebuilt in the near future. In addition, the current operating guide which is to open the Colley Road to Brick Church 69-kV line for the loss of the Colley Road to Brick Church 138-kV line can be eliminated.

ATC and the city of Madison have proposed to bury part of the two Blount-Ruskin 69-kV overhead lines underground. This project will be completed in 2011.

In the 2008 Assessment, ATC planned to install a 12.24 MVAR 69-kV mobile capacitor bank at the Brick Church Substation. Due to the new load forecast changes, the plan has been changed. The new location for the mobile capacitor bank is Spring Green substation. It will not only help to support the area 69-kV system voltages under the Spring Green transformer outage, but also reduce load curtailment risk during several planned line construction outages in this area during 2009-2010 timeframe.

Projects whose “Need date” precedes the “In-service date”

Construct Oak Ridge-Verona 138-kV line

• The need year is listed as 2009. However, due to regulatory delays, the in-service year is 2010. The mitigation measures for the potential 2009 system violations include upgrading the existing Verona and New Glarus 69-kV capacitor banks (2007), rebuilding the Stoughton 69-kV bus (2009) and distribution load shifting at Stoughton.

Uprate McCue-Lamar 69-kV line

• Due to an enhanced generation dispatch scenario utilized in the 2008 Assessment , potential single-contingency low voltage problems in the Lamar area and an overload of the McCue-Lamar 69-kV line were observed in the 2009 summer peak model. Considering reasonable project lead times, the 2010 in-service date was chosen for this provisional project of uprating the McCue-Lamar line and installing capacitor banks at Lamar. In the interim, dispatching Sheepskin generation could be one possible mitigation strategy to address these constraints.

Jefferson-Tyranena-Stony Brook 138-kV line and associated line uprates

• The construction of a new 138-kV line from Jefferson Substation to Stony Brook Substation has previously been identified as the long-term solution to the voltage problems in this area. The PSCW issued an order to ATC in August of 2006 for the construction of this line with an expectation that it would be completed by 6/1/2008. However, several legal challenges have limited ATC’s ability to complete the detailed design, procure necessary materials, and procure the necessary easements to support start of construction in the fall of 2007 in order to meet this in-service date. As an interim measure, ATC decided to install a temporary 24.5 MVAR 138-kV capacitor bank at Boxelder in 2008 to address the imminent voltage constraints.

Projects whose “In-service date” precedes the “Need date”

As a result of in-service date flexibility and corresponding alignment with other ATC project needs, the following project will be in service prior to the need date. Additionally, the project listed below is asterisked in the Annual Project Tables.

• Uprate X-23 Colley Road-Marine 138-kV terminals

Please refer to Methodology & Assumptions for a designation of the dispatch scenario