20171218PAC to Staff Attachment Utah_DPU 10.11c.docx

Team,
Below is a summary of the status, philosophy, and background for your reference.
Paul Henry
Project Manager
Huntington SPS Summary – November 1, 2012
Summary:
The Huntington Special Protection System (SPS) was designed and implemented as part of the Three Peaks 345 kV Source Cedar City, Utah, TZCE/2006/C/001. The purpose of the Huntington SPSis to prevent overloading of the Sigurd phase shifting transformer and prevent transmission system low voltage in the event of a line loss during heavy system load conditions.
Status:
Presentations were made to the Western Electricity Coordinating Council’s Remedial Action Scheme Reliability Subcommittee (WECCRASRS). Conditional approval was given on April 30, 2010 and full approval was given on November 17, 2010. The Huntington SPS system achieved monitoring mode status on July 6, 2012 and active mode status is anticipated before year end 2012.
The Huntington SPS presently only requires settings installed for generator tripping for the loss of the Sigurd – Three Peaks – Red Butte 345 kV line. It is anticipated that the Huntington SPS will not likely reach arming levels prior to the installation of the second Sigurd – Red Butte 345 kV line, after which time the Huntington SPS will not be required. For the present,Grid Operations has made the decision to simply monitor the flows on the Huntington – Pinto 345 kV line and the Sigurd – Three Peaks 345 kV line and operate to the higher limit of 715 MW and 730 MW respectively which will be below the Huntington SPS arming level.
Philosophy:
Although the Huntington SPS presently only trips generation for loss of the Sigurd-Three Peaks or the Three Peaks-Red Butte 345 kV lines, it is designed for future tripping of generation for the loss of the Huntington-Pinto or the Pinto-Four Corners 345 kV lines. For heavy TOT 2B/2C north to south transfers, the loss of the Sigurd-Red Butte 345 kV line may overload the Sigurd phase shifting transformer beyond the emergency limit, and may cause low voltages below criteria in the Pinto area transmission system. Ultimately, under the same conditions, the loss of the Huntington-Pinto or Pinto-Four Corners 345 kV line may overload the Sigurd phase shifting transformer beyond the emergency limit, and may cause low voltages below criteria in the Three Peaks/Red Butte area transmission system. The Huntington SPS is designed to trip generation to maximize path capability.
Background:
Prior to the addition of the Sigurd – Red Butte – Harry Allen 345 kV line in 1990, a Huntington generator tripping scheme was available to trip generation for the loss of the Huntington – Pinto or Pinto – Four Corners 345 kV lines to maximize the transfer capability of the Huntington – Pinto – Four Corners 345 kV and the Sigurd – Glen Canyon 230 kV lines. After the addition of the Sigurd – Red Butte – Harry Allen 345 kV line, the Huntington – Pinto or Pinto – Four Corners 345 kV line was the limiting outage for determining the transfer capability of the entire path. Huntington generator tripping, for loss of the Huntington – Pinto or Pinto – Four Corners 345 kV line, was utilized to maximize the path capability.
Over the next 17 years, the Red Butte load has increased substantially, from 90 MW in 1990 to approximately 350 MW in 2007. The loss of the Sigurd – Red Butte 345 kV line then limited the overall transfer capability of the southern Utah transmission path. The Huntington generator tripping was no longer required for the loss of the Huntington – Pinto or Pinto – Four Corners 345 kV line due to the path limitations imposed by a Sigurd – Red Butte 345 kV line outage. However, with the continued load growth at Red Butte and the substantial load addition to the Sigurd – Red Butte 345 kV line with the addition of the Three Peaks project, Huntington generator tripping was again projected as a requirement for the loss of the Sigurd – Three Peaks or the Three Peaks – Red Butte 345 kV line, and also for the loss of the Huntington – Pinto or the Pinto – Four Corners 345 kV line, to maintain the committed transfer capability on the southern transmission path.
Since 2007, the loads have not increased as projected, and will not likely reach the level requiring the Huntington SPS prior to the installation of the second Sigurd – Red Butte 345 kV line. Therefore, it is anticipated that transmission system loading will not reach a level requiring the Huntington SPS. As a precautionary measure, Grid Operations has opted to limit the loading on the Huntington – Pinto 345 kV line and the Sigurd – Three Peaks 345 kV line.