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30 CHAPTER SIX ELECTRICAL TRANSMISSION INFRASTRUCTURE This chapter reviews the existing body of information on the potential impacts of electrical transmission infrastructure on airports and aviation. Electrical transmission infrastructure includes transmission towers and the electrical lines that they carry. This infrastructure supports the energy-generation tech- nologies discussed in previous sections allowing the power generated by the facility to be delivered to load centers in pop- ulated areas. Potential impacts to airports and aviation from transmission lines include physical penetration of airspace and communication systems interference. PHYSICAL PENETRATION OF AIRSPACE Electric transmission lines and the towers that support them can rise high enough to impact airspace. The transmission towers that hold up the electrical lines are the tallest part of the facility (see Figure 21). The towers are typically constructed of a lattice steel frame and range between 50 and 180 ft in height depending on the size of the electrical line being carried, among other factors (IFC 2007), although transmission towers exist that are as tall as 1,100 ft (Alimak HEK 2011). COMMUNICATION SYSTEMS INTERFERENCE Electromagnetic interference can be produced by high-voltage transmission lines. The level of potential interference can vary depending on the design voltage capacity of the line and the FIGURE 21 Transmission tower schematic (courtesy: HMMH). distance of a sensitive receptor from the line. Leaks occurring between the conductor and the insulators or metal fittings are referred to as a corona discharge. Typically, concern about electromagnetic release is confined to 345 kV or greater lines. EXAMPLES MITIGATION OPTIONS Transmission towers associated with the Blythe Plant's elec- trical line are proposed to be 145 ft tall. Shorter poles (90 ft Mitigation options associated with electrical transmission are tall) will be employed along a 3,900-ft segment that passes limited. The best option is to locate transmission infrastruc- through an airport influence area. After consultation with the ture so as to avoid physical penetration of airspace and inter- Riverside County Airport Land Use Commission, the line ference with communications systems. A design option is to was moved an additional 1,000 plus feet to the west (CEC place corona rings on high-voltage lines at the conductor 2010b). The CEC required marking and lighting of all trans- hardware interface points at the end of the insulators to reduce mission poles in the 3,900 ft airport influence area, which the potential effects of electromagnetic interference. was not a condition of the FAA's No Hazard Determination.