United States Radiation Programs ORPEAD78-1
Environmental Protection Las Vegas Facility March 1978
Agency PO Box 15027
Las Vegas NV 89114
Radiation
v>EPA A Comparison of
Measurement Techniques
to Determine Electric Fields
and Magnetic Flux Under
EHV Overhead Power
Transmission Lines
-------
Technical Note
ORP/EAD 78-1
A COMPARISON OF MEASUREMENT
TECHNIQUES TO DETERMINE ELECTRIC
FIELDS AND MAGNETIC FLUX UNDER
EHV OVERHEAD POWER TRANSMISSION LINES
Donald L. Lambdin
March 1978
OFFICE OF RADIATION PROGRAMS - LAS VEGAS FACILITY
ELECTROMAGNETIC RADIATION ANALYSIS BRANCH
SURVEILLANCE AND INSPECTION DIVISION
U.S. ENVIRONMENTAL PROTECTION AGENCY
LAS VEGAS, NEVADA 89114
-------
DISCLAIMER
This report has been reviewed by the Office of Radiation Programs,
U.S. Environmental Protection Agency, and approved for publication. Mention
of trade names or commercial products does not constitute endorsement or
recommendation for their use.
11
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PREFACE
The Office of Radiation Programs of the U.S. Environmental Protection
Agency carries out a national program designed to evaluate population
exposure to ionizing and nonionizing radiation, and to promote development
of controls necessary to protect the public health and safety. This
report examines magnetic field strengths and compares electric field
strength measurement techniques under extra-high-voltage overhead power
transmission lines. Readers of this report are encouraged to inform the
Office of Radiation Programs of any omissions or errors. Comments or
requests for further information are also invited.
Floyd L. Galpin, Director
Environmental Analysis Division
Office of Radiation Programs
111
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TABLE OF CONTENTS
Page
LIST OF FIGURES v
LIST OF TABLES v
ACKNOWLEDGaXEWr vi
INTRODUCTION 1
SITE DESCRIPTION 1
INSTRUMENTATION 1
PROCEDURES 2
Electric AC Field Strength Measurements 2
Magnetic Flux Measurements 2
RESULTS 3
Electric Field Strength Profiles 3
Magnetic Flux Profiles 6
SUMMARY AND CONCLUSIONS 6
REFERENCES 10
APPENDIX 11
Electric Field Strength and Magnetic Flux Measurements 12
IV
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LIST OF FIGURES
Number Page
1 Electric Field Strength Profiles Using a
Polytech FBM-100 4
2 Electric Field Strength Profiles Using a Monroe
Electronics Model 238A-1 5
3 Magnetic Flux Profile 7
LIST OF TABLES
Number Page
1 Observed Differences in Line Current and Magnetic
Flux Measurements 8
v
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ACKNOWLEDGMENT
The author is grateful to Messrs. Edwin Mantiply and Patrick J. O'Brien
for their assistance in making measurements under Maryland's hot summer skies.
The efforts of Sandi Graves in helping type and ready this report for publication
in this decade are also greatly appreciated.
VI
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INTRODUCTION
This report examines the maximum magnetic field strengths associated with
normal procedure electric field strength measurement techniques under a 500 kV
overhead power transmission line. Additionally, comparisons are made between
U.S. techniques and a technique reportedly used in the USSR for measuring
electric fields under EHV overhead transmission lines. Information received
subsequent to this study indicates that the supposed Russian technique was not
used, having been found to produce noticeable errors.
SITE DESCRIPTION
The measurement site was located in Frederick County, Maryland, about
three miles south of Buckeystown on a farm belonging to Mr. Eugene Mills. The
line under which the measurements were made was the Potomac Edison Company
510kV Doubs Conastone Line. The line was a single three-phase circuit with
each bundle consisting of two conductors of 1.8 inch diameter spaced 18 inches
apart and oriented horizontally, each bundle being spaced 35 feet apart. An
open, unused hay field was selected between two support towers that was flat
and free from vegetative or geographic anomalies. Short hay stubble and new
weed growth varied in height from about 6 inches to about 18 inches. On the
days the measurements were taken, July 27 and 28, 1976, the weather was hot
and very humid with temperatures in the high 80's and humidity approaching 100
percent.
A Ranging, Inc. Model M100 optical tape measure rangefinder was used to
optically determine line heights. Ten readings were made before and after
data was collected. The average height after correction of meter error and
inclusion of head height above ground was 46.3 feet.
INSTRUMENTATION
Two instruments were used to measure electric field strengths, one of
which was also capable of measuring magnetic flux. Primary electric field
strength and magnetic flux measurements were made using a Polytech Model FBM-
100 field meter. This instrument is capable of measuring electric field
strengths ranging from about 0.1 V/m to 3MV/m. It is also equipped with an
adapter box and auxiliary probes which allow measurement of magnetic flux
(.0001 to 300 gauss), space potential, short circuit current, and open circuit
voltage.
Supplemental electric field strength measurements were made using a
Monroe Electronics Model 238A-l,field meter. This instrument has been fully
described in a previous report.
1
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PROCEDURES
ELECTRIC AC FIELD STRENGTH MEASUREMENTS
The measurement procedure was that described in an earlier report. A
200 foot profile line, perpendicular to the center phase of the transmission
line at its minimum height above ground, was established using a non-metallic
100 foot tape measure. The observer-meteraxis was perpendicular to the
transmission line, with the observer's back toward the line. Measurements
were made employing three different geometries with each of the two instruments.
The first geometry was that normally used in this country, holding the instrument
at one meter above ground level and at least one meter from the observer (two
meters from the observer when using the Polytech FBM-100). The second method
was one reportedly employed in the U.S.S.R. (later evidence indicated this
not to be true), holding the meter as if attached to an 11 inch handle at 1.8
meters above ground level. A third geometry was chosen, holding the meter 1.8
meters above ground, but using the long handle technique employed in the first
geometry. A few comparative measurements were made using a fourth geometry,
holding the meter as if on an 11 inch handle, at one meter above ground.
The first two geometries were of primary interest, in effect comparing
U.S. and assumed U.S.S.R. techniques. Therefore, measurements were made at
three foot intervals when using the Polytech instrument. Nine foot intervals
were used for the third geometry and when using the Monroe meter, since fewer
measurement points were required for comparisons. Only a few measurements
were made employing the fourth technique at random distances.
In all cases, care was taken to maintain the same geometry at each measurement
site. Only one individual made all measurements as it had been previously
determined that different persons caused significantly different meter readings
for a given measurement site and geometry. Each instrument was held at the
maximum practical distance from the body for each defined handle length.
Instrument handles were marked so they would be held at the same points each
time a measurement was made.
MAGNETIC FLUX MEASUREMENTS
Since magnetic flux measurements are not significantly influenced by the
presence of an observer, only two geometries were used: one placing the
sensing coil at one meter above ground, the other, with the coil 1.8 meters
above ground. Before making measurements, care was taken to determine the
position of the observer and coil relative to the power line which would
maximize measured values. It was found that the observer should hold the coil
handle parallel to the direction of the power line. Since the magnetic field
curves in space, the coil was rotated at each position for a maximum reading.
Measurements were taken at three foot intervals for the first one hundred feet
and at nine foot intervals thereafter.
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RESULTS
ELECTRIC FIELD STRENGTH PROFILES
Figure 1 illustrates the electric field strength profiles for three
geometries using the Polytech FBM-100. The solid line curve represents the
calculated theoretical profile. As expected, the measurement technique using
a short handled instrument at 1.8 meters above ground, produces the highest
observed values. This is due to the field focusing effect of the observer.
Figure 2 shows electric field strength profiles measured with the Monroe
Electronics Model 238A-1. This meter has been used in previous studies and
.is used here for comparison with the Polytech instrument. Approximately the
same relative deviation is shown between long-handled and short-handled
techniques using either instrument. Ratios of electric field strength data
were calculated, comparing the short-handled technique (first geometry) with
the long-handled technique (second geometry). The Polytech instrument data
showed ratios varying from 1.44 to 1.73 (average 1.58). Using the Monroe
instrument, the ratio varies from 1.14 to 1.60 (average 1.40). The slight
differences between the two meters is probably explained by the necessity of
holding the shorter handled Monroe instrument closer to the observer for the
long-handled technique measurements. When compared, using identical geometries
(1.8 meters above ground with an 11 inch handle), the Monroe and Polytech
instruments give essentially the same results.
2
Louise B. Young, in her report to the EPA, described a similar differ-
ence, using a Monroe Model 238A-1. Ms. Young reports observed ratios of 1.5
to 2.0 with an average of 1.6. The slight difference between Ms. Young's
ratios and those reported here is probably due to different methods of holding
the meter, especially with the more critical 11 inch handle.
The influence of observer position with respect to the instrument is
shown by comparing data for the third geometry (long handle at 1.8 meters
above ground) with the first geometry (short handle at 1.8 meters above ground).
The most pronounced difference occurs when using the Polytech instrument,
where the observer stands two meters from the instrument when using the long
handle. (It can be seen that the Polytech measured values using the long
handle at 1.8 meters above ground actually more closely approach the measurements
using the long handle at one meter above ground.) The average ratio between
measurements at 1.8 meters above ground and at one meter above ground, using
the long handle, is only 1.10. The average ratio using the short handle is
1.58. Therefore, the technique employing a short handle significantly distorts
the open field measurement. Comparing the same geometries, but using the
Monroe instrument, shows that the shorter four foot handle of the Monroe also
causes significant pertubations of the field. The average ratio between long
handle techniques at 1.8 meters and at one meter is 1.22, compared to 1.10 for
the Polytech.
3
-------
9.0.
8.0.
7.0.
6.0-
5.0-
£
**
CO
2
iZ 4.0-
u
u
V
3.0-
2.0-
1.0-
510 kV Doubs-Conastone
Potomac Edison Co.
Line Height = 46.3 ft.
* Short Handle @ 1.8 m.
o Long Handle @ 1.8 m.
• Long Handle @ 1 m.
00
i^ I I i r I
200 180 160 140 120 100
I I
I
80 60 40 20
Distance from Center Phase (ft.)
I I I
0 -20 -40 -60
FIGURE 1. ELECTRIC FIELD STRENGTH
PROFILES USING A POLYTECH FBM-100
-------
9.0.
8.0.
7.0-
6.0-
f 5.0-
01
IZ 4.0-
o
°>
3.0-
2.0.
1.0.
510 kV Doubs-Conastone
Potomac Edison Co.
Line Height = 46.3 ft.
A Short Handle (g) 1.8 m.
o Long Handle @ 1.8 m.
• Long Handle (53 1 m.
o
o o
I I 1 I I I I I I I I
200 180 160 140 120 100 80 60 40 20 0
Distance from Center Phase (ft.)
I I
-20 -40 -60
FIGURE 2. ELECTRIC FIELD STRENGTH PROFILES
USING A MONROE ELECTRONICS MODEL 238A-1
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A few measurements were made using the fourth geometry (an 11 inch handle
held at one meter above ground). There was no significant difference between
readings made at one meter above ground regardless of effective handle length
for either meter. The small differences observed were neither significantly
less than nor greater than corresponding reference measurements. Other studies
have shown a shielding effect by the observer at this measurement height.
Measurements made at one meter above ground with the Polytech instrument
show very good correlation with calculated values, and with values measured in
November 1974 at the same location. The Monroe meter showed some deviation
from calculated values and previously measured values, especially in the
higher electric fields. This may have been due to slightly different measure-
ment techniques than those used in previous studies by different observers.
MAGNETIC FLUX PROFILES
Figure 3 shows magnetic flux profiles measured with the Polytech Model
FBM-100 with the sensing coil held at one meter and at 1.8 meters above ground.
The two techniques produce virtually identical measured values at distances
greater than 100 feet from the center phase. Over the first 100 feet, the
average ratio between measurements at 1.8 meters and at 1.0 meter is only 1.07
and does not exceed 1.09. The magnetic flux values range from 0.006 gauss at
198 feet to 0.097 gauss near the center phase. A broad peak averaging about
0.09 gauss extends over the area covered by the three phases. The sharp, well
defined peaks occurring for the electric field measurements are not observed
here. The angle of the coil axis with respect to ground varies from 0°(coil
parallel to ground) to 90° at 50 feet from the center phase, and 160° at 200
feet from the center phase. The change in angle is uniform and gradual as
distance increases.
On the second day of measurements, a significant anomaly occurred (see
Table 1). Measurements on that day were consistently higher by a factor of
1.35 (35 percent) than those taken on the previous day. This difference could
not be adequately accounted for. The line current increased by only five
percent. The meter functions were operating correctly with no change in
readings due to range switching. Also, geometries were carefully duplicated.
Further study is needed to define the cause of this anomaly.
SUMMARY AND CONCLUSIONS
A study was made of electric field strengths and magnetic flux under a
510 kV overhead power transmission line. Electric field strength measurements
were made using two instruments and three geometries, with brief reference to
a fourth geometry. Magnetic flux measurements were made with one
instrument, using two geometries.
The two meters, Monroe Electronics Model 238A-1 and Polytech Model FBM-
100, were found to give essentially identical responses when used with handles
of equal length.
6
-------
to
2. .10,
"- .09,
08,
.07,
.06,
.05,
.04,
.03,
.02,
.01.
510 kV Doubs-Conastone
Potomac Edison Co.
Line Height = 46.3 ft.
o 1.8 m. above ground
• 1 m. above ground
o°o«> o 0°o
Q o o ooo
00
•o
*>
•9
•o
o o
200 180 160 140 120 100 80 60 40 20 0 -20 -40 -60
Distance from Center Phase (ft.)
FIGURE 3. MAGNETIC FLUX PROFILE
_ J
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TABLE 1
OBSERVED DIFFERENCES IN LINE CURRENT
AND MAGENTIC FLUX MEASUREMENTS
DATE RATIO
7/27 7/28 Day I/Day 2
Voltage (kV) 510 510
Current in Each
Phase (Amps) 567 595 1.05
Magnetic Flux
6 Feet From Center
Phase (Typical) .085 .115 1.35
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Until recently, some observers in the U.S.S.R. reportedly used techniques
for making electric field measurements under powerlines which differed in
geometry from those used in the U.S. Using the same instrument, measurements
with the assumed Soviet technique result in values about 1.4-1.6 times higher
than those using the U.S. technique. These observations agree with those
reported by Louise B. Young. Di Placido et al., have recently provided
theoretical results for various measurement techniques, emphasizing the short
handle method, which are in close agreement with the experimental observations
discussed here. Information received after this report was written indicates
that the short-handle technique is not used in the U.S.S.R.
The major observed difference in measured values, when using differing
geometries, occurs at 1.8 meters above ground level. The closer the observer
is to the instrument, the higher the electric field strength. Measurements
made at one meter above ground level are not as critically affected by position
of the observer with respect to the measuring device.
Holding the instrument at least two meters from the observer minimizes
variations in measured values due to changes in height of the instrument above
ground level. Measurements made at one meter and at 1.8 meters above ground
level are essentially the same if an effective two meter handle is used.
Magnetic flux measurements are not significantly affected by position of
the observer with respect to the sensing coil. The magnetic flux increases by
a factor of 1.09 or less in the area directly under the three phases of the
transmission line when the coil is elevated from one meter to 1.8 meters above
ground level. Magnetic flux measurements are significantly affected by angular
orientation of the coil. They are also affected by changes in current flow
through the transmission lines; further studies should be made to determine
the relationship between magnetic flux and current flow.
-------
REFERENCES
1. R. A. Tell et al. , "An Examination of Electric Fields Under EHV Overhead
Power Transmission Lines," EPA-52012-76-008, United States Environmental
Protection Agency, April 1977.
2. L. B. Young, Report to the United States Environmental Protection Agency
on Effects of Extremely High Voltage Transmission, received July 1, 1975.
3. J. Di Placido, C. H. Smith and B. J. Ware, "Analysis of the Proximity
Effects in Electric Field Measurements," American Electric Power Service
Corporation, New York, NY, presented at the 1978 IEEE Power Engineering
Society Winter meeting.
10
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APPENDIX
ELECTRIC FIELD STRENGTH AND MAGNETIC FLUX MEASUREMENTS.
11
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ELECTRIC FIELD STRENGTH (kV/m)
MONROE ELECTRONICS
MODEL 1238A-1
POLYTECH MODEL FBM-100
MAGNETIC FLUX (GAUSS)
POLYTECH MODEL FBM-100
llstance
From
Center
Phase
(Ft.)
-36
-27
-24
-21
-18
-15
-12
-9
-6
-3
0
3
6
9
12
15
18
21
24
27
30
Long Handle
@ 1 Meter
Above
Ground
4.15
3.95
3.75
3.7
3.7
3.65
3.7
3.6
4.2
4.9
Long Handle 11" Handle 11" Handle Long Handle Long Handle 11" Handle
@ 1.8 Meters @ 1 Meter @ 1.8 Meters @ 1 Meter @ 1.8 Meters @ 1 Meter
Above Above Above Above Above Above
Ground Ground Ground Ground Ground Ground
4.8 3.5 3.9
4.6 3.4 3.7
4.4 3.2 3.6
4.4 3.2 3.6
4.4 3.2 3.5
4.4 5.4 3.1 3.6 3.3
4.6 4.2 3,0 3.6
3.0
2.9
4.4 4.2 3.0 3.5
3.0
3.3
4.8 5.6 3.6 4.0
. 3.75
4.0
5.8 6.8 4.3 4.9
4.8
11" Handle
@ 1.8 Meters
Above
Ground
5.4
5.3
5.25
5.1
4.9
5.0
4.8
4.7
4.8
4.9
4.8
5.1
5.4
5.7
6.2
6.75
7.3
1 Meter
Above
Ground
.078
.083
.085
.085
.085
.087
.089
.087
.085
.094
.085
.088
.090
.088
.088
.087
.088
.087
.084
.084
.083
1.8 Meters
Above
Ground
.084
.092
.097
.095
.096
.095
.096
.092
.091
.093
.091
.096
.097
.096
.095
.093
.095
.095
.092
.091
.091
Angle
Of
Probe
70°
0°
45°
-------
ELECTRIC FIELD STRENGTH (kV/m)
MONROE ELECTRONICS
MODEL 1238A-1
POLYTECH MODEL FBM-100
MAGNETIC FLUX (GAUSS)
POLYTECH MODEL FBM-100
listance Long Handle
From 0 1 Meter
Center Above
Phase Ground
(Ft.)
33
36 5.7
39
42
45 5.7
48
51
54 5.0
57
60
63 4.3
66
69
72 3.4
75
78
81 2.6
84
87
90 2.1
93
96
Long Handle 11" Handle 11" Handle Long Handle
Q 1.8 Meters @ 1 Meter @ 1.8 Meters @ 1 Meter
Above Above Above Above
Ground Ground Ground Ground
4.7
6.7 7.9 5.0
5.2
6.9 5.0
6.7 7.7 4.9
4.75
4.6
6.0 6.8 4.3
4.0
4.0
5.8 3.75
3.4
3.2
4.5 2.9
2.7
2.4
3.6 2.1
2.0
1.8
2.8 1.9
1.7
1.6
Long Handle 11" Handle 11" Handle
@ 1.8 Meters @ 1 Meter @ 1.8 Meters
Above Above Above
Ground Ground Ground
7.6
5.6 7.5
7.7
5.6 8.1
7.7
7.4
7.3
4.8 7.1
6.4
6.0
4.0 5.7
5.3
4.9
3.2 4.5
4.2
3.7
2.4 3.4
3.2
2.9
2.05 2.85
2.7
2.5
1 Meter
Above
Ground
.080
.080
.077
.073
.071
.068
.065
.060
.057
.053
.050
.047
.045
.042
.040
.038
.036
.033
.032
.029
.028
.027
1.8 Meters
Above
Ground
.091
.084
.084
.079
.075
.070
.070
.065
.061
.056
.052
.048
.046
.045
.042
.040
.038
.035
.033
.031
.029
.027
Angle
Of
Probe
60°
90°
105°
120°
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ELECTRIC FIELD STRENGTH (kV/m)
MOW ROE ELECTRONICS
MODEL 1238A-1
POLYTECH MODEL FBM-100
MAGNETIC FLUX (GAUSS)
POLYTECH MODEL FBM-100
Distance Long Handle
From @ 1 Meter
Center Above
Phase Ground
(Ft.)
99 1.65
102
105
108 1.3
111
114
117 1.1
120
123
126 0.88
129
132
135 0.70
138
144 0.60
153 0.45
162 0.40
171 0.35
180 0.28
189 0.25
198 0.20
Long Handle 11" Handle 11" Handle Long Handle
@ 1.8 Meters @ 1 Meter @ 1.8 Meters @ 1 Meter
Above Above Above Above
Ground Ground Ground Ground
2.2 1.5
1.35
1.2
1.6 1.9 1.1
1.1
1.05
1.3 1.0 1.5 0.95
0.80
0.80
1.05 1.22 0.79
0.65
0.60
0.85 1.0 0.60
0.70 0.85 0.48
0.60 0.48 0.72 0.40
0.50 0.38 0.60 0.38
0.40 0.32 0.50 0.32
0.36 0.28 0.43 0.275
0.32 0.38 0.25
0.28 0.32 0.20
Long Handle
@ 1.8 Meters
Above
Ground
1.6
1.45
1.35
1.25
1.15
1.1
1.05
0.90
0.88
0.81
0.75
0.70
0.64
0.53
0.48
0.41
0.35
0.30
0.25
0.215
11" Handle 11" Handle 1 Meter
@ 1 Meter @ 1.8 Meters Above
Above Above Ground
Ground Ground
2.3
2.2
2.0
1.9
1.7
1.05 1.6
1.5
1.38
1.30
1.20
0.67 1.12
1.0
0.97
0.80
0.45 0.69
0.40 0.60
0.32 0.51
0.27 0.43
0.36
0.31
.025
.023
.019
0.17
.015
.013
.011
.0095
.009
.008
.007
.006
Above Of
Ground Probe
.026
.023
135'
.006
160°
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TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
1. REPORT NO.
ORP/EAD 78-1
3. RECIPIENT'S ACCESSION NO.
4. TITLE AND SUBTITLE
A COMPARISON OF MEASUREMENT TECHNIQUES TO DETERMINE
ELECTRIC FIELDS AND MAGNETIC FLUX UNDER EHV OVERHEAD
POWER TRANSMISSION LINES
5. REPORT DATE
March 1978
6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
Donald L. Lambdin
8. PERFORMING ORGANIZATION REPORT NO.
9. PERFORMING ORGANIZATION NAME AND ADDRESS
U.S. Environmental Protection Agency
Office of Radiation Programs
P.O. Box 15027
Las Vegas, Nevada 89114
10. PROGRAM ELEMENT NO.
11. CONTRACT/GRANT NO.
12. SPONSORING AGENCY NAME AND ADDRESS
Same as above
13. TYPE OF REPORT AND PERIOD COVERED
Technical Note
14. SPONSORING AGENCY CODE
15. SUPPLEMENTARY NOTES
16. ABSTRACT
Comparison is made between techniques used by the U.S. and reportedly used by the
U.S.S.R. to measure electric field strengths under a 500 kV overhead power
transmission line. Magnetic flux measurements were also made. Two instruments
and three geometries were used in the electric field strength portion of the
study. Maximum differences were noted when the measuring instrument was
positioned close to the observer and at 1.8 meters above the ground as compared
to one to two meters from the observer.
17.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.lDENTIFIERS/OPEN ENDED TERMS
C. COSATI Field/Group
Electric field strength measurements
Magnetic flux measurements
EHV overhead power lines
18. DISTRIBUTION STATEMENT
19. SECURITY CLASS (This Report/
Unclassified
21. NO. OF PAGES
20. SECURITY CLASS (This page)
Unclassified
22. PRICE
EPA Form 2220-1 (Rev. 4-77)
PREVIOUS EDITION IS OBSOLETE
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