An Extra High Voltage (EHV) Overlay is a collection of 500+ kV transmission projects to be added to the existing transmission system to facilitate the economic transfer of power and reduce congestion across the grid.

SPP developed the EHV Overlay concept in 2006 under the direction of the Transmission Working Group. Its first report, published in June 2007, along with additional materials and subsequent studies may be found on this page. 

The EHV Overlay plan looks beyond SPP's geographic borders and the traditional 10-year planning horizon, establishing a long-range, region-wide vision for transmission expansion. SPP developed the plan using a value-based planning approach, keeping in mind the increasing need for a robust transmission system. The proposed overlay not only delivers economic value to the SPP footprint, but also supports system reliability, future markets, wind integration, and more.

To address the complexities of planning, building, and allocating the cost of the EHV transmission backbone, SPP has adopted a new Integrated Transmission  Planning (ITP) methodology. The ITP, which approved by the SPP Board of Directors in October of 2009, will integrate three existing processes: the EHV Overlay, Balanced Portfolio, and annual reliability assessment. The ITP will bring the EHV Overlay into SPP's planning and cost allocation processes.

Beginning in January 2010, SPP will perform its planning duties in accordance with the ITP. Read the detailed ITP process document for more information.