Agenda - Council - 06/25/2013 - Laserfiche WebLink

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Enterprise Park to Crooked Lake 115 kV Transmission Line March 2012 Environmental Assessment immediately under a transmission line and dissipates rapidly within the right-of-way to either side. FM radio receivers usually do not pick up interference from transmission lines because corona generated radio frequency noise currents decrease in magnitude with increasing frequency and are quite small in the FM broadcast band (88-108 Megahertz). Also, the excellent interference rejection properties inherent in FM radio systems make them virtually immune to amplitude type disturbances. A two-way mobile radio located immediately adjacent to and behind a large metallic structure (such as a steel tower) may experience interference because of signal -blocking effects. Movement of either mobile unit so that the metallic structure is not immediately between the two units should restore communications. This would generally require a movement of less than 50 feet by the mobile unit adjacent to a metallic tower. Utility Systems and Public Services in the Project area include AM and FM radio; television; global positioning systems (GPS); existing utilities; cellular signals; and emergency service providers (e.g., "911" and emergency management systems (EMS)). Communications networks in the Project area were identified through a search of current antenna licenses with the Federal Communication Commission (FCC). Existing transmission lines in the Project area were identified by the Applicant in the route permit application. Transmission lines have the potential to interfere with existing utilities through corona and gap discharges. Corona is a phenomenon associated with energized transmission lines. Under certain conditions, the localized electric field near an energized conductor can be sufficiently concentrated to produce a tiny electric discharge that can ionize air close to the conductors. This partial discharge of electrical energy is called corona discharge or corona (Electric Power Research Institute, 1982 as cited in PG and E, 2005). Several factors, including conductor voltage, shape and diameter, and surface irregularities, such as scratches, nicks, dust, or water drops, can affect a conductor's electrical surface gradient and its corona performance (PG and E, 2005). Corona from transmission lines could generate electromagnetic signals in the same frequencies as those used for radio and television signals, depending on the frequency and strength of the radio and television signal. Corona discharges cause short pulses of voltage and current to be propagated along the transmission line, resulting in radio frequency noise in the vicinity of the line (PG and E, 2005). In addition to corona, gap discharges also may be present. These types of discharges could occur "at locations where tiny electrical separations (gaps) develop between mechanically connected metal parts. A small, electric spark discharge across the gap can create unwanted electrical noise" (PG and E, 2005). Generally, interference due to gap discharges is less frequent for high voltage transmission lines than lower voltage lines (PG and E, 2005). Interference issues from transmission lines generally could be corrected by tightening any loose or separated parts on the transmission lines (BPA, 2002). 29