Refer to Table ZS-4 and Figure ZS-20

Summary of key findings

• Heavy load growth in Waukesha, Washington, Dodge and Jefferson counties will require voltage and load support. A new 345-kV line from Rockdale to Mill Road (formerly Lannon Junction) is one option being considered but not yet proposed to solve these problems.
• Voltage and thermal issues remain in Zone 5 under contingency conditions.

Eleven 138-kV buses in Waukesha and Washington County experience marginal bus voltage under NERC Category A or TPL-001-0 conditions (intact system) in 2023.  The fifteen buses are Allerton (95.8%), Bark River (95.6%), Barton (95.8%), Cooney (95.5%), Cottonwood (95.2%), Hartford (95.1%), Merrill Hills (95.6%), St. Lawrence (95.6%), Summit (95.4%), Arthur Road (95.6%), and Glacier (955%).

Following are the results of the 2023 contingency analysis (NERC Category B or TPL-002-0 conditions) performed on Zone 5.

The Oak Creek–Pennsylvania 138-kV line will load to 106.3% of its summer normal rating under intact system conditions. Under a number of contingencies, the line can exceed it summer emergency rating by up to 7.8%.

Splitting the Concord 138-kV bus will result in low or marginal 138-kV bus voltage at Hartford (88.7%), St. Lawrence, Arthur Road (90.8%), and Cooney (90.3%).

An outage of the Saukville–Fredonia 138-kV line will cause the bus voltage at Fredonia to drop to 89.2%.

Splitting the Pleasant Prairie 345-kV bus between bus sections 3 and 4 will cause Bain transformer #5 to exceed its summer emergency rating by 59.7%.  Bus outages are low probability events. Relief can be provided by reducing the output of Pleasant Prairie generator #2 to about 350 MW.

An outage of the Bain–Kenosha 138-kV line will cause the Albers–Kenosha 138-kV line to exceed its summer emergency rating by 4.0%.

An outage of the Oak Creek–Pennsylvania 138-kV line will cause the Branch–Kansas 138-kV line (119.9%), Nicholson – Ramsey 138-kV line (99.4%), and Oak Creek – Ramsey 138-kV line (99.2%) to approach or exceed their summer emergency ratings. 

Splitting the Burlington 138-kV bus will result in low 138-kV bus voltage at Tichigan (0.831) and Burlington (0.842).

An outage of the Arcadian 345/138-kV transformer #1 causes Arcadian transformer #3 to load to 118.9% of its summer emergency rating and Arcadian transformers #2 to load to 97.5% of its summer emergency rating.

In the previous 2018 results section, a potential Rockdale–Mill Road 345-kV line was discussed as a way improving bus voltages in Waukesha, Washington, and Jefferson Counties. Through 2018, the ATC planning models indicated there is generation available at Concord and Germantown that could provide support to the three county region. At some point between 2018 and 2023, all of the generation at Concord and Germantown will be dispatched. Dispatching generation at Concord and Germantown has been able to provide voltage and thermal relief.  When all the generation has been dispatched, no additional relief will be available and it will be time to consider other system improvements to provide relief.

Summary of Compliance with NERC Standards

The mitigation plans, planned, proposed and provisional projects identified for Zone 5 in this Assessment will allow the ATC system in Zone 5 to meet NERC standards TPL-001, TPL-002, TPL-003 and TPL-004 in each of the four years 2009-2013, and for the 2014-2018 planning horizon.