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Transcript
5.7 ELECTRIC AND MAGNETIC FIELD EFFECTS Although a discussion of electric and magnetic field (EMF) effects is not specifically required by regulation in a CPCN, Panda-Brandywine has elected to provide this information to agencies and the public to continue Panda's policy of keeping the agencies and public informed so that they may better understand the project. As discussed in Section 3.2.7, Panda proposes to install a total of approximately 8 miles of 230-kV transmission line. In order to minimize impacts to surrounding communities, Panda proposes to install nearly all (at least 95 percent) of their transmission line in existing rights-of-way, specifically, the Conrail railroad right-of-way and an existing PEPCO transmission line right-of-way. The 4.5 miles of transmission line that follow the existing Conrail railroad right-of-way will require new structures; the remaining 3 miles will be strung on existing PEPCO structures. Except where the conductors must be configured horizontally to pass under PEPCO's 500-kV transmission line, Panda will use a vertical (or stacked) configuration to minimize electric and magnetic fields at the edge of the right-ofway. The vertical configuration will use single-pole structures; lattice structures will be required for crossing under the 500-kV transmission line. Panda has modeled the EMFs associated with their proposed transmission line. These results show that the calculated fields at the edge of the actual Conrail right-of-way, as well as the PEPCO rights-of-way, are below the standards or guidelines set by those states that have standards or guidelines for EMFs. A discussion of EMFs in general, EMF research, state guidelines and standards, and the results of Panda's EMF modeling are presented in the following paragraphs. Electric transmission lines have been in service in Maryland and the United States for many years. According to the Office of Technology Assessment (1989), today in the United States there are about 350,000 miles of transmission lines and about 2,000,000 miles of distribution lines. Transmission line voltages range between 69 and 765 kV; primary distribution line voltages generally range between 2.4 and 35 kV. These lines are located in all types of land uses, including urban, suburban, agricultural, wetlands, and open-country areas. Transmission lines generate an electric field because of the unbalanced electrical charge on the conductors resulting from the voltage of the transmission lines. Because the charge and voltage on the conductors change polarity at a rate of 60 times per second (cycles per G-BRCPCN.2/57.1--082693 second or Hertz [Hz]) in the United States, the EMFs also vary at a frequency of 60 Hz (i.e., powerline frequency). Current does not have to be flowing in an object for an electric field to exist; magnetic fields, however, are the result of a current flowing through a conductor. The stronger the current, the more intense the magnetic field. We are surrounded daily by EMFs. The earth itself generates a static electric and magnetic field. Fields associated with 60-Hz alternating currents are found in home appliances, house wiring, electric distribution lines, and transmission lines. For transmission lines, electric field intensities are expressed as kilovolts per meter (kV/m); magnetic fields (flux density) are usually reported either in microteslas (μT) or milligauss (mG) where 1 μT = 10 mG (1 mG = 0.1 μT). The typical electric and magnetic fields (produced at powerline frequencies) encountered in daily life are given below (Davis, 1993): Situation Electric (kV/m) Magnetic (mG) Home wiring At electrical appliances Under distribution lines serving homes Inside railroad cars on electrified lines Under high-voltage transmission lines 0.001-0.010 0.030-0.300 0.010-0.060 --1-7 1-5 5-3,000 1-10 10-200 25-100 The static background of the earth's electric field is about 0.120 kV/m and the earth's magnetic field is about 500 mG . In a letter that accompanies an annual report commissioned by the MDNR Power Plant Research Program and the Maryland PSC (Energetics, 1992), MDNR states that: “...human exposure to EMF is unavoidable and occurs from diverse sources, such as electric transmission and distribution lines, wall wiring, lighting fixtures, radio, television, appliances and computers. These sources are much more common and could be far greater contributors to EMF than those emitted by high voltage transmission lines.” Davis (1993) points out that within the United States, per capita consumption of electricity has increased by nearly a factor of 1000, and yet there has been no trend toward increasing birth defects. Similarly, Valberg (1993) says that although electric power consumption has increased dramatically during this century, mortality has decreased as dramatically, with the steepest decline (greater than ten-fold) occurring in the 5-to 14-year age group. With regard to childhood leukemia, according to Brown et al. (1989) and Linet and Devesa (1991), G-BRCPCN.2/57.2--082693 childhood leukemia today has not increased over 1950 levels even though there has been a ten-fold increase in per capita consumption of electric power. Nonetheless, some state agencies working with various research groups as well as the electric utilities have attempted to devise standards for EMF even though at this time no positive link has been established between EMF exposure and adverse health impacts. Some of the regulations that have been established to date are summarized below: Electric (kV/m) Magnetic (mG) StateMax. Edge Max. Edge Montana (residential) Minnesota (informal guideline) New Jersey (guideline) New York (interim policy) North Dakota Oregon Florida 500-kV 230-kV -8 --9 9 1 -3 1.6 --- ------- ---200 --- 10 8 2 2 --- 200 150 Montana has the most stringent standard for electric fields, 1 kV/m at the edge of the rightof-way. In a recent conversation with Mr. Art Compton, Chief of the Facility Siting Bureau, Montana Department of Natural Resources and Conservation (personal communication, 1993), Mr. Compton stated that they “no longer consider the [EMF] standard useful.” Mr. Compton said that Montana had no basis for the standard and that by the next legislative session, he expected the standard to be repealed. Presently, no national regulations exist for exposure durations in any country. A report by Carnegie Mellon University (1989) states the following: “The International Radiation Protection Association [IRPA], whose mission is to review scientific evidence and propose safety standards, has issued draft exposure guidelines for power-frequency electric and magnetic fields. They call for a limit of 5 kV/m for continuous exposures to electric fields and 2 Gauss (2000 mG) for magnetic fields.” In summary, there is no definitive link between exposure to EMF associated either with transmission lines or appliances in the home (for example) and illness. Nonetheless, some utilities and state agencies are adopting policies to regulate the public's exposure to EMF. G-BRCPCN.2/57.3--082693 Panda-Brandywine has considered these policies in their selection of a transmission line right-of-way and in their transmission line design. In quantifying and evaluating the effects of the proposed 230-kV transmission line that extended from the Brandywine site to PEPCO's Burches Hill Substation, Panda's contractor, Gilbert/Commonwealth, has used two computer models. These models were Southern California Edison's FIELDS, the output of which was verified by the Electric Power Research Institute's (EPRI's) ENVIRO computer program. The latter model provides the maximum value of EMF at 1 meter above ground, as recommended by the Institute of Electrical and Electronic Engineers (IEEE) standard. For the model, the ground is assumed to be flat, and no shielding object is assumed to occur in the right-of-way (i.e., worst-case conditions). The minimum right-of-way required for NESC clearances is 45 ft wide, using an 840-ft maximum span. This value easily fits within the Conrail right-of-way, which at its narrowest width, is 66 ft wide. The transmission line configuration used to model the EMF and radio influence (RI) is shown in Table 5.7.0-1. Because two different conductor types (single and double [bundled]) are being considered by Panda, EMF effects for each must be considered. The results are discussed below. 5.7.1 ELECTRIC AND MAGNETIC FIELDS 5.7.1.1 New Single-Circuit 230-kV Transmission Line Panda will install a single-circuit 230-kV transmission line that will lie within and follow the Conrail right-of-way for about 4.5 miles. This right-of-way, at its narrowest, is 66 ft. Panda, when discussing modeling results, has used a conservative width of 60 ft (defined by the model as -10 to +50 ft, relative to the center of the transmission line structure) for all right-of-way values. Single-pole transmission line structures will be located on the west side of the rails; the conductors will be suspended over the rails, i.e., away from the edge of the right-of-way. A vertical (or stacked) configuration will be used to reduce EMF at the edge of the right-of-way. Panda proposes to use two types of conductor: (1) bundled, and (2) single. The bundled conductor will be used from the Brandywine Substation to a point about 2.8 miles, at which time Panda's transmission line will cross underneath PEPCO's existing 500-kV transmission line. The bundled conductor is used to further reduce RI in the vicinity of the U.S. Air Force's Globecom communication facility. From the 500-kV transmission line on into PEPCO's Burches Hill Substation, a distance of about 5.2 miles, single conductor will be used. G-BRCPCN.2/57.4--082693 The modeling results of the single and bundled conductor are shown in Tables 5.7.1-1 and 5.7.1-2, and Figures 5.7.1-1 and 5.7.1-2. According to these modeling results, the maximum electric field for either conductor occurs at a point about 3 ft above the ground and +10 ft (east) relative to the center of the transmission line structure. This is very close to being directly below the mid-span of the transmission line where the clearance to ground (from the lowest conductor) is a minimum of 36 ft (well within NESC standards for height above the ground). The electric field maxima at +10 ft are 1.12 and 1.46 kV/m. At the western and eastern edge of the right-of-way (-10 ft and +50 ft, respectively), the electric field strengths for the single conductor are 0.89 and 0.52 kV/m, respectively. For the bundled conductor, the values are 1.17 and 0.67 kV/m, respectively. Electric field strengths decrease rapidly with distance. At a distance of 100 ft from the centerline of the structure, the electric field strength is only 0.04 and 0.06 kV/m (i.e., only 5 percent of the right-of-way value) for single and bundled conductor, respectively. At 1,000 ft, the electric field is reduced to about 0.3 percent or 0.003 kV/m. Because Maryland does not have EMF rules, these values are compared with rules or guidelines from other states (please refer to earlier table). Panda's maximum electric fields on the right-of-way for either conductor type are at least four times lower than the electric field rules or guidelines of every state. Moreover, the electric field strengths at the edge of the modeled right-of-way width of 60 ft are below the edge right-of-way standards of every state except Montana, which has a very conservative value of 1 kV/m for residential areas. The actual right-of-way width is at least 66 ft wide, and in many instances wider, which means that the electric field at the edge of the actual Conrail right-of-way is in all likelihood below every states' edge-of-right-of-way standard. A maximum magnetic field of 32.8 mG (for single and bundled conductor) was calculated using Southern California Edison's FIELDS computer program. This value occurs 3 ft above the ground at a point +10 ft from the centerline of the structure, which virtually coincides with the location of the conductor which at midspan has a clearance of 36 ft. At the western and eastern edge of the modeled right-of-way (-10 and +50 ft), the magnetic field is 29.5 and 24.0 mG, respectively (see Figure 5.7.1-2), for either conductor type. The highest value (29.5 mG) represents only about one-fifth of the lowest allowable magnetic field standard at the edge of the right-of-way (Florida--150 mG for a 230-kV line). The magnetic field also decreases with distance. At 100 ft from the centerline of the structure, the magnetic field is only 8.8 mG (i.e., about 30 percent of the value at the edge of the right- G-BRCPCN.2/57.5--082693 of-way); at 1,000 ft, the magnetic field is 0.2 mG (i.e., 10,000 times less than the exposure guidelines drafted by IRPA for magnetic fields). 5.7.1.2 Panda 230-kV Circuit Collocated with PEPCO's Existing Transmission Lines EMF was also modeled for PEPCO's 250-ft right-of-way with and without Panda's 230-kV transmission line located on the south side of the southernmost of PEPCO's structures. In order to provide the most conservative (i.e., worst-case) results, Panda's heaviest load (winter 1996) is compared with PEPCO's lighter load (summer 1992). The results for the electric field are summarized below: Loading Case Electric Field (kV/m) Under At Edge of Line Right-of-Way 1992 Summer (without Panda) 2.0 0.2 1996 Winter (with Panda) 2.0 0.2 Although the electric field maxima are higher (2 kV/m) than the maxima calculated in the Conrail right-of-way, the maximum electric field strength is only 0.2 kV/m at the edge of the PEPCO right-of-way. This value for the edge of the right-of-way is well below any state's standard for the edge of the right-of-way. The results for magnetic fields are summarized below: Loading Case Magnetic Field (mG) Under At Edge of Line Right-of-Way 1992 Summer (without Panda) 70.8 5.9 1996 Winter (with Panda) 73.9 23.8 Again, the maxima for the magnetic field are greater; however, like the electric field, the magnetic field of 23.8 mG at the edge of the PEPCO right-of-way is well below any state standard for the edge of the right-of-way. Panda will use a technique called reverse phasing to reduce the magnetic field. Reverse phasing can be used whenever a double circuit configuration exists. Each circuit consists of three conductors (A, B, and C). By arranging the phasing of the second set of conductors G-BRCPCN.2/57.6--082693 such that it is C, B, and A, the magnetic field emitted by one circuit is partially canceled by the field emitted by the second circuit. 5.7.1.3 Panda 230-kV Crossings of PEPCO's 500-kV Circuits Panda's 230-kV transmission line will cross PEPCO transmission lines twice on their way to the Burches Hill Substation. The first crossing after leaving Panda's Brandywine Substation will occur about 2.8 miles north along the Conrail right-of-way. At this point, Panda's single-circuit 230-kV line will pass under one of PEPCO's double-circuit 500-kV transmission lines. According to Panda's modeling results, where the conductor configuration is horizontal on two crossing towers, the electric field will be increased by about 30 percent directly under the centerline of the conductors. The magnetic flux density directly below the centerline of the conductors will be increased by about 38 percent for summer 1992 loads and about 25 percent for winter 1996 loads. This increase in EMF will occur only in the immediate vicinity (i.e., about 150 along the PEPCO right-of-way) of the crossing. In order to obtain NESC clearance for the new 230-kV line between the 500-kV line and the ground, it is necessary to divert from the Conrail right-of-way for a distance of about 150 ft west, then cross under the 500-kV line for a distance of about 175 ft, then reverse direction for about 150 ft east back to the Conrail right-of-way. For a total distance of 300 ft, Panda's 230-kV line parallels the 500-kV line. The following table presents the results of modeling the EMFs for this situation: Electric Field (kV/m) Magnetic Field (mG) Under At Edge of Under At Edge of Loading Case Line Right-of-Way Line Right-of-Way 1992 Summer (without Panda) 3.2 2.3 36.9 35.1 1996 Winter (with Panda) 3.2 2.3 41.5 41.5 The second crossing of PEPCO's transmission line occurs about 2,500 ft southeast of the Burches Hill Substation. At this point PEPCO's two existing double-circuit 500-kV transmission lines, which run from PEPCO's Burches Hill Substation to Chalk Point and Moss Point, cross over Panda/PEPCO's two double-circuit 230-kV transmission lines in the vicinity of Clinton Acres residential development. The modeling of EMF used the electrical G-BRCPCN.2/57.7--082693 loading represented by PEPCO's 1992 summer loading without Panda generation and 1996 winter loading with Panda generation. According to the model results, there is no increase in existing electric field resulting from Panda's additional power transmission. The increase in magnetic field resulting from Panda's transmission amounts to only a 1.8 mG increase at the edge of the 500-ft wide right-of-way. 5.7.2 RADIO INFLUENCE The corona effect also produces some limited RI. RI levels were calculated using an EPRI computer program. Heavy rain was the assumed weather condition for the model run. The radio noise levels expected in the vicinity of Panda's single-circuit, 230-kV transmission line are given in Tables 5.7.2-1 and 5.7.2-2 (Lapwing and 2-Cuckoo conductors, respectively). These results, in turn, are summarized in Table 5.7.2-3. For the single conductor at a frequency of 500 kiloHertz (kHz) at a distance of 300 ft from the transmission line centerline the radio noise level is 39.7 dB above 1 microvolt per meter (μV/m) in heavy rain (Table 5.7.2-1). For the bundled conductor, all values are approximately 11 dBA lower than for the single conductor (Table 5.7.2-2). The U.S. Air Force's Globecom communication facility boundary abuts the eastern edge of Conrail's right-of-way and again is approximately 30 ft from the centerline of the transmission line structures. The use of bundled conductor is planned especially to minimize the RI of the proposed 230-kV transmission line in the vicinity of Globecom. The Globecom receiving antenna is approximately 1,000 ft east of the Conrail/Globecom property line. From Table 5.7.2-3, it is seen that the estimated maximum radio interference level diminishes with distance from the line at 1,000 ft during heavy rain, and for the frequencies of 500, 1,000, and 1,600 kHz the estimated maximum radio interference levels are 28.0, 23.0, and 19.0 dB above 1 μV/m respectively. No interference with the Globecom facility is expected. G-BRCPCN.2/57.8--082693