Vantage to Pomona FEIS Index 34 - Laserfiche WebLink

Home Browse Search

Vantage to Pomona Heights Chapter 2 230 kV Transmission Line Project FEIS Proposed Action and Alternatives PAGE 2-74 1970s. Since that time, energy demand in the Yakima Valley has continued to grow. Pacific Power’s planning studies have identified the loss of their existing Pomona-Wanapum 230 kV Transmission Line as the single most critical outage risk on the Mid-Columbia system. Transmission systems in the United States must be planned, operated, and maintained so that they meet the NERC reliability standards. Additionally, transmission systems in the western United States must also meet the reliability standards of the WECC. Pacific Power's existing transmission system in the Yakima area no longer meets these reliability standards due to load growth in the Yakima area. Pacific Power participated in a regional transmission system planning study (NTAC 2007) to address reliability issues within the Mid-Columbia transmission system. To address these problems the Mid- Columbia utilities including BPA, Grant County PUD, Chelan County PUD, Pacific Power, and Puget Sound Energy worked together with the NWPP, NTAC to study the Mid-Columbia transmission system and define needed reinforcements. The Wanapum/Midway-Vantage Area 230 kV study was completed in November 2007. The study determined that loss of Pacific Power’s existing Pomona-Wanapum 230 kV Transmission Line would result in a significant load shedding exposure on the transmission system and would also impact other transmission providers in the Mid-Columbia area with overloads of existing transmission components. Based on 2007 loads and system activity during high load periods in the Yakima Valley, loss of the Pomona-Wanapum 230 kV Transmission Line would result in the need to shed up to 167 megawatts (MW). This load shed would occur through five different substations and would represent 33 percent of the 500 MW load in the Yakima area. Load shedding means that power would not be able to be delivered and available to the Yakima area because power delivery would have to be curtailed to prevent the overload and failure of parallel transmission systems serving the Yakima area as explained below. The regional transmission study showed an outage of Pacific Power’s existing Pomona-Wanapum 230 kV Transmission Line would result in redistribution of electrical flow across the BPA and Grant County PUD parallel transmission systems that also feed into Pacific Power’s Yakima load area. This redistribution then results in loadings well above the acceptable limits of many existing transmission components on the other systems putting the regional transmission system at risk of failure. The transmission system planning studies determined that an outage of Pacific Power’s existing Pomona-Wanapum 230 kV Transmission Line would result in the overload of three Pacific Power high voltage transmission lines and two BPA high voltage transmission lines, potentially causing service interruptions in the Yakima Valley. The regional planning study showed that the addition of the new Vantage to Pomona Heights 230 kV Transmission Line Project would eliminate the redistributed loads and the overloading of the adjacent transmission system. The planned line would mitigate the risk discussed above and ensure compliance with NERC and WECC mandatory reliability standards. Each existing and proposed transmission element must comply with the system performance requirements of NERC reliability standards and WECC system performance standards. If the standards are not meet then the Pacific Power transmission system would be in violation of the mandatory NERC and WECC reliability standards in the Yakima area and be subject to NERC compliance and enforcement action. In 2012 WECC revised standards regarding transmission line separation. WECC revised the standard related to Adjacent Transmission Circuits. It modified the distance between the structure centerline separation from “less than the longest span length of two transmission circuits at the point of separation or 500 feet to separation between their centerlines less than or equal to 250 feet at the point of separation” (WECC 2013).