Refer to Table ZS-1 and Figure ZS-17

Summary of key findings

• Many of the line loading and low voltage issues in Zone 5 occur as a result of opening substation bus tie breakers.
• New generation in the greater Milwaukee area will drive many system improvements in Zone 5 within the next decade.

Nine 138-kV buses in Waukesha and Washington Counties experience low bus voltages under NERC Category A or TPL-001-0 conditions (intact system) in 2009.  The nine buses are Concord (93.5%), Bark River (94.2%), Cooney (92.8%), Cottonwood (93.1%), Germantown (93.6%), Hartford (94.9%), Merrill Hills (94.7%), Maple (94.1%), and Summit (92.9%).  These low intact system bus voltages occurred because Concord and Germantown generation was modeled out of service in 2009 as a result of new generation at Oak Creek.  A new 650-MW generator is scheduled to be placed in service prior to the summer of 2009.  In addition, two-32.4 MVAR capacitor banks are scheduled to be placed in service at the Summit Substation by June of 2010 to improve area bus voltages. In the interim, dispatching Concord and/or Germantown generation will provide var support to improve area voltage. 

Thermal and low voltage issues also are expected to occur elsewhere in Zone 5.  Following are results of the contingency analysis (NERC Category B or TPL-002-0 conditions) performed on Zone 5.    

An outage of the Jefferson–Crawfish River–Concord 138-kV line will cause the bus voltages at Concord (87.8%), Cooney (89.0%), and Summit (89.7%) to drop below 90%.  Running Concord generation will alleviate this situation.

An outage of the Bark River–Cottonwood 138-kV line will cause bus voltages at Cooney (89.3%), Cottonwood (87.7%), and Summit (89.1%) to drop below 90%.  Running Concord generation will alleviate this situation.

An outage of the Bark River–Sussex 138-kV line will cause bus voltages at Cooney (89.6%), Cottonwood (88.0%), Bark River (88.0%), Germantown (89.4%), and Summit (0.894) to drop below 90%.  Running Concord and Germantown generation alleviate this situation.

An outage of the Maple–Saukville 138-kV line will cause bus voltages at Cooney (90.0%), Cottonwood (89.2%), Bark River (89.6%), Germantown (84.1%), Maple (83.8%) and Summit (89.9%) to decrease drop below 90%.  Running Germantown generation will alleviate this situation.

An outage of Hartford–St. Lawrence 138-kV line will cause low bus voltage at Hartford (86.8%).  Running Concord generation will improve the bus voltage at Hartford.

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%.  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 Bain–Albers 138-kV line to load to 97.6% of its summer emergency rating. Increasing line conductor clearances will alleviate this situation by permitting operation above 167 degrees.  

An outage of the Arcadian 345/138-kV transformer #1 causes Arcadian transformer #3 to load to 106.0% of its summer emergency rating and Arcadian transformers #2 to load to 96.0% of its summer emergency rating.  Project development is underway to replace the Arcadian transformers #2 and #3 with a single 500 MVA transformer.  The 345/138-kV windings of the existing transformers are rated at 239/239 MVA (SN/SE).  The summer emergency rating of the new transformer will be 640 MVA.

Splitting the Oak Creek 230-kV bus between bus sections 6 and 7 will cause Oak Creek transformer T884 to load to 97.5% of its summer emergency rating.  Bus outages are considered low probability events.

Oak Creek generation: We Energies received PSCW approval to build two 650-MW coal powered generators at the Oak Creek Power Plant. The units are scheduled to go into service in 2009 and 2010. The following projects are under construction as a result of this new generation.

2009 - Oak Creek generation Phase 1

• build a new Oak Creek 345-kV switchyard to interconnect one new 650-MW generator
• reconductor a segment of the Oak Creek-Ramsey 138-kV line
• terminate the Ramsey–Harbor line into the Kansas/Norwich substations creating a Kansas–Harbor 138-kV line and a Norwich–Ramsey 138-kV line
• reconductor the Oak Creek-Allerton 138-kV line
• replace current transformers at the Racine 345-kV Substation
• replace two 345-kV circuit breakers at Pleasant Prairie Substation on the Racine and Zion lines with IPO breakers and upgrade relaying
• expand Oak Creek 138-kV switchyard to connect the 345/138-kV, 500 MVA transformer

2010 - Oak Creek generation Phase 2

• expand 345-kV switchyard at Oak Creek Power Plant to interconnect a second new 650-MW generator           
• reconductor the Oak Creek-Root River 138-kV line
• uprate terminal equipment and increase line clearances on the Oak Creek-Nicholson 138-kV line to permit operation at 230 degrees
• Increase line rating of the Kansas – Ramsey 138-kV line

In response to customer requests for new distribution interconnections, new 138-kV bus sections will be constructed at the Pleasant Valley, Shorewood and Brookdale Substations in 2009.