Field strength measurements on a single row of panels indicates that the operational mode of the array as configured presents no radiated EMI problems. Only one relatively significant frequency band near 200 kHz showed any degree of intensity (9 muV/m including a background level of 5 muV/m). The level was measured very near the array (at 20 ft distance) while Federal Communications Commission (FCC) regulations limit spurious emissions to 15 muV/m at 1,000 ft. No field strength readings could be obtained even at 35 ft distant

Herke, F. P., Jr.

Johnson, J. A.

Knapp, W. D.

English

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https://ntrs.nasa.gov/search.jsp?R=19770015664 2020-03-22T09:15:14+00:00Z
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PHOTOVOLTAIC SYSTEM TEST FACILITY ELECTRO-
MAGNETIC INTERFERENCE MEASUREMENTS
J. A. Johnson, F. P. Herke, Jr. , and W. D. Knapp
National Aeronautics and Space Administration
Lewis Researcb Center
Cleveland, Ohio 44135
April 1977
b
MAY 1977
RECEIVED
NASA STI FACILITY
INFJT BRANCH
Prepared for
ENERGY RESEARCH AND DEVELOPMENT ADMINISTRATION
Office of the Assistant Administrator for
Solar, Geothermal, and Advanced Energy Systems
Division of Solar Energy
Under Interagency Agreement E(49-26;-1022
SI	 Report No 2	 Government Accession No. 3.	 Recipient's Catalog No
NASA TM X-73640
4	 Tale and Subtitle 5	 Report Date
PHOTOVOLTAIC SYSTEM TEST FACILITY ELECTRO- April 1977
6	 Performing Organization Code
J
MAGNETIC INTERFERENCE MEASUREMENTS
--
7.	 Author(s) 8.	 Performing Organization Report No
J. A. Johnson, F. P. Herke, Jr., and W. D. Knapp E-9142
10	 Work Unit No
9	 Performing Organization Name and Address
Lewis Research Center 11,	 Contract or Grant No
National Aeronautics and Space Administration
Cleveland, Ohio	 44135 13.	 Type of Report and Period Covered
Technical Memorandum
_
12	 Sponsoring Agency Name and Address
Energy Research and Development Administration
14	 Sponsoring Agency CodeDivision of Solar Energy
Washing ton, D.C.	 20545
15	 Supplementary Notes
This report was prepared under Interagency Agreement E(49-26)-1022
16	 Absn act
Early ( c pring of 1976) EMI tests were conducted on several solar cell panels of the ERDA
Photovoltaic System Test Facility without power conditioning to determine the characteristic
radiated interference frequencies. 	 This test was conducted using a manually switched
resistive load of approximately 360 W at a 1 Hz rate. 	 Later (early summer) tests were
conducted at an ar ray output of approximately 1. 5 kW while interfacing with an available line
commutated type of inverter. 	 The ERDA Photovoltaic System Test Facility as configured
appears to present very few problems associated with common everyday appliances such as
radio and television sets with regard to both radiated and conducted interference. 	 Further,
field strength measurements on a single row of pi—iels indicates that the operational mode of
the array as configured presents no radiated EMI problems. 	 Only one relatively significant
frequency band near 200 kHz showed any degree of intensity (9 uV/m including a background
level of 5 µV/m).	 However, the level was measured very near the array (at 20 ft distance)
while Federal Communications Commission (FCC) regulations call for these measurements
at 1000 ft.	 FCC regulations limit spurious emissions to 15 µV/m at 1000 ft. 	 No field
strength readings could be obtained even at 35 ft distant.
17	 Key Words (Suggested by Author(sl) 19,	 Distribution Statement
Unclassified - unlimited
STAR category 44
ERDA category UC-63
19	 Security	 Classif. (of this report)
	 	 20	 Security C,ass,f. (of this page) 21.	 No	 of Pages 22.	 Price'
Unclassified UnclassifiedT
For sale by the National Technical Infumatlon Service Springfield. Virginia 22161
YI	 i
PHOTOVOLTAIC SYSTEM TEST FACILITY
ELECTROMAGNETIC INTERFERENCE MEASUREMENTS
by J. A. Johnson, F. P. Herke, Jr. and W. D. Knapp
INTRODUCTION
During construction of the ERDA Photo lroltaic System Test Facility
located at the L&.:is Research Center, Cleveland, Ohio, electromagnetic
interference measurements were made in order to determine or isolate any
N
conducted or radiated interference frequencies peculiar to the photovoltaic
i
w
array or the associated power conditioning equipment. It was necessary to
determine if the system 5 array or the associated power conditioning equipment
could possibly cause interference on assigned frequencies of nearby airport
communication and navigation information channels as well as problems with
nearby residential radio, stereo and television sets.
Although the operation of a photovoltaic array is not specifically
covered by the Federal Communications Commission (FCC) rules and regulations,
the following guidelines are being adhered to: first, FCC rules and regula-
tions (Ref. 1) Vol. II, Part 18, Subpart H, .-egarding miscellaneous equipment,
specified requirements under procedures similar to those for diathermy equip-
ment permitting such changes in the procedure as may be required due to the
nature of the particular equipment involved. Operation of diathermy equipment
(or "miscellaneous equipment") at frequencies other than specifically assigned
or reserved is recognized but emission of any radio frequencies generated by
such operation, including spurious and harmonic emissions, are not to ex-eed
a field strength of 15 microvolts per meter at a distance of 1000 feet or more.
Second, the Lewis Research Center further restricts any potential interference
emissions to not more than 10 microvolts per meter at the laboratory boundaries.
-2-
DESCRIPTION OF THE FACILITY
The facility is comprised of an array of solar cell modules mounted
on 20 - 4' x 8' panels in the arrangement shown in Figure 2. Figure 1 is
an overall plan view or plot arrangement of the installation using a simu-
lated aerial photo. The flat panels are oriented directly south and pre-
set at an angle equal to the latitude in degrees for the site location (410).
The modules are connected in 24 series strings and are paralleled at terminal
boards in the trailers (reference panel configuration - Figure 3) to estab-
lish an open-circuit voltage of approximately 2ZOV DC. The panels extend for
approximately 207 ft. in a row. Power conditioning equipment is mounted in
two trailers approximately 300 ft. distant and is connected to the array via
underground conduit with sufficient copper conductivity to limit transfer
losses to 3% from the field to control center power conditioning equipment.
A block diagram is shown in Figure 4 showing component arrangement. Position-
ing a Stoddard field intensity instrument at a distance of 20 ft. from the
array utilizing a trial process was necessary to establish a suitable basis
for comparison that would yield adequate readings on the intensity indicator
(IjV/meter s-ale). Levels decreased as expected the farther the instrument
was moved from the array and disappeared completely into the background noise
level at a distance of 35 ft.
DESCRIPTION OF TESTS
Solar Array Only
Tests were conducted to search for the dominant characteristic frequencies
that could be expected near the array (array acting as an antenna). The first
test was conducted without any power conditioning equipment connected in order
to establish a baseline for further testing as well as to isolate or identify
any dominant characteristic frequencies (see Figure 2 initial array layout).
if
IWAWMW
-3-
This first test was accomplished by abruptly interrupting the array current
of approximately 2 amperes into a resistive load at a power level of 360 watt.
The array out put was feeding a resistive load and the load was switched on
and off at a 1 Hz rate utilizing a manually operated toggle switch while a
Stoddard field intensity instrument model NM 20B was utilized to search for
the peak level of any dominant frequencies.
Line commutated inverter connected to the photovoltaic array. - A second
test was later conducted with power conditioning equipment connecte% utilizing
a line commutated inverter operat'Lig at approximately a 1.5 kW level. The
line commutated inverter is one which is synchronized with a utility grid and
the 60 Hz line frequency is used to commutate the switches (e.g., silicon con-
trolled rectifiers) on and off at the proper intervals. Figure 4 shows a
simplified schematic of the configuration under test. Modules were connected
in series strings to supply approximately 1 700 VDC at the inverter input under
load conditions.
Portable commercial AC/DC radio and television sets were utilized to
survey the AM/FM and VHF/UHF bands, respectively, in order to qualitatively
evaluate their susceptibility to any conducted or radiated interference fer-
quencies generated in and about the control center as well as the array proper.
Operation was compared off an isolated AC utility bus versus operation
directly off the inverter AC output. In addition, AC/DC sets were operated
on both AC and DC (batteries) to permit distinguishing between conducted and
radiated interference.
TEST RESULTS
A plot of the array emission frequencies identified in test No. 1 is
shown in Figure 5. Frequencies associated with the line commutated inverter
IE
-4-
(test No. 2) are also shown along with the array emission frequencies
(test No. 1).
Field strength measurements, for the
STF configuration of a single row of 20 solar panels, indicates operation
v
of the array presents no radiated electromagnetic interference problems.
All detectable extraneous emission frequencies, while testing in an
operational mode (with inverter interface), yielded only one measurable
frequency band near 200 kHz at a level of 9 microvolts per meter including
a background level of 5 microvolts per meter. This level was measured very
near the array (at 20 ft.) while the FCC regulations call for measurements
at 1000 feet - at which point spurious emissions must be below 15 microvolts
per meter. Field strength readings could not be obtai^ed at a distance
i
greater than 35 ft.
It will be noted that the frequencies as shown in Figure 5 lie a
upper end of the low-frequency (T,-F) 30-300 kHz band and the lower en
the medium frequency (M-F) 300-3000 kHz band. These frequencies fall
bands allocated by the FCC to international fixed public, fixed Alask
aeronautical mobile as well as aeronautical radio-navigation usage.
Some radiated interference in the AM band was noted in the immed
vicinity of the control room which could be eliminated by antenna rec
or relocation of the receiver to a position approximately 20 ft. away
inverter. The same condition was noted within 0.5 ft. of each panel
box where the cable shielding is interrupted at the terminal blocks;
the interference faded out only 0.5 ft. further away.
tI
-5-
CONCLUSIONS AND RECOMMENDATIONS
No electromagnetic interference problems were detected with the photo-
v., :taic array per se in an operational mode while interfaced with a line
commutated inverter and as the array field is configsred herein.
It is recommended that these tests be repeated periodically as the array
size (capacity) is increased and different power conditioning equipment becomes
available, e.g., self-commutated inverters, maximum power trackers, batteries,
etc.
REFERENCES
1. Miscellaneous Equipment. Federal Communications Commission
Rules and Regulations, vol. II, pt. 18, subpt. H, Sept. 1972.
1. 1
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Photovoltaic system test facility electromagnetic interference measurements

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