Download 5 - Maryland Public Service Commission

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
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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),
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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.
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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.
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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-
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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
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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
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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.
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