**Middle Columbia Transmission Overview and Constraints:**

Geographically, the transmission system under discussion covers the
Washington counties: Okanogan, Chelan, Douglas, Grant, Kittitas, and
Yakima. Loads in the area are winter peaking. A normal, winter peak
condition is characteristic of high east-to-west flows (West of
Cascades-North and West of Cascades-South) and very light north-to-south
(NS) flows (North of John Day). A normal, summer peak condition is
characteristic of moderate east-to-west flows and high NS flows (North
of John Day and North of Hanford). *The summer pattern produces the
highest stress for the area.* The normal, peak summer condition exposes
the area to a number of thermal constraints.

The area load centers are: Okanogan PUD, Chelan and Douglas PUD, Grant
PUD, and PAC-Yakima.

The transmission system must perform to provide power to the area load
centers during different seasonal conditions while supporting the
surplus power transfers from the Columbia River hydro generation
interconnected in the area. These hydro plants include Grand Coulee,
Chief Joseph, Wells, Rocky Reach, Rock Island, Wanapum, and Priest
Rapids. The Northwest loads are winter peaking with a large portion of
the total load located west of the Cascades in the Puget Sound and
Portland/Vancouver/Willamette Valley load centers. During normal, peak
winter conditions surplus Mid-Columbia generation transfers east-to-west
across the Cascades. During normal, peak summer conditions surplus
generation transfers east-to-west across the Cascades, at low levels,
and heavy NS transfers exist on the Mid-Columbia 500-kV and 230-kV
system. Summer power transfers to California and reduced loads in the
Northwest produce heavy NS flows.

The summer NS transfers are apparent on both the 500-kV and the 230-kV
transmission. A large portion of the hydro generation in the area is
connected at 230-kV and 115-kV:

  --------------------- --------------- ----------- ------------------------
  **Major Generation**  **Connected**   **Owner**   **Max MW Capability**

  Grand Coulee          500-kV          BPA         4598

  Grand Coulee          230-kV          BPA         2250

  Chief Joe             500-kV          BPA         1265

  Chief Joe             230-kV          BPA         1320

  Wells                 230-kV          Douglas     855

  Rocky Reach           230-kV          Chelan      1331

  Rock Island           115-kV          Chelan      646

  Wanapum               230-kV          Grant       1090

  Priest Rapids         230-kV          Grant       1006

  Total Connected at                                **5863 MW**
  500-kV                                            

  Total Connected at                                **8499 MW**
  230-kV and 115-kV                                 
  --------------------- --------------- ----------- ------------------------

The 230-kV and 115-kV generation will step up to the 500-kV system on
500/230-kV transformers (TXF) at Grand Coulee (1 TXF), Chief Joseph (1
TXF), Sickler (1 TXF), and Vantage (2 TXF\'s) substations. The remainder
of the surplus generation transfers NS on the 230-kV system to Midway
substation and moves further south to Bonneville, Big Eddy, White
Bluffs, and Benton substations. The area 230-kV and 115-kV line loadings
are highly sensitive to the generation levels at Wells, Rocky Reach,
Rock Island, Wanapum, and Priest Rapids. Grand Coulee and Chief Joe
generation will impact the 230-kV and 115-kV loading, but to a lesser
degree.

During the heavy NS pattern the 230-kV transmission is utilized to its
full capacity. The 230-kV transmission south of the Vantage/Wanapum
substation is heavily stressed during low Priest Rapids generation in
the spring and summer months. The low Priest Rapids generation is a
function of operating the Columbia River for biological/fish
requirements.

**Constraints on New Wind Generation Interconnections:**

The Mid-Columbia area has been identified as a prime location for new
wind generation. However, during the spring and summer months, with
heavy NS transfers on the 230-kV system and Columbia River Hydro
operations necessary to meet biological/fish requirements, the existing
transmission is at full capacity. New wind generation interconnecting on
the 230-kV or 115-kV transmission north of Midway will add to the local,
surplus generation and will increase the NS transfers. In order to
provide a safe and reliable interconnected power system significant
upgrades are required on the Mid-Columbia 230-kV system to support
existing generation transfers and new wind generation interconnecting on
the 230-kV or 115-kV transmission.