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Jay Johnson 24 June, 2011 Slide 1/18
Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-
94AL85000. This work was funded by the US Department of Energy Solar Energy Technologies Program.
Photovoltaic DC Arc Fault Detector Testing at Sandia National Laboratories
Jay Johnson1, Birger Pahl2, Charles Luebke2, Tom Pier2, Theodore Miller3, Jason Strauch1, Scott Kuszmaul1, and Ward Bower1
1 Sandia National Laboratories, Albuquerque, NM 2 Eaton Corporation, Milwaukee, WI3 Eaton Corporation, Pittsburgh, PA
Jay Johnson 24 June, 2011 Slide 2/18
Presentation Outline
PV Arc Fault Background
Sandia National Labs Overview
Arc Fault Detection Challenges
Arc Fault Experiments• Inverter noise• Arcing noise• Arc vs baseline comparison on
multiple PV strings
Conclusions
Jay Johnson 24 June, 2011 Slide 3/18
Sandia Contribution to PV Arc Fault Detection and Mitigation Requirements
Arc faults in PV systems cause fires.
Module damage modeling -80.0
-70.0
-60.0
-50.0
-40.0
-30.0
-20.0
-10.0
0.0
10.0
20.0
1.00E+00 1.00E+01 1.00E+02 1.00E+03 1.00E+04 1.00E+05 1.00E+06 1.00E+07
Mag
nitu
de (
dB)
Frequency (Hz)
Frequency Response for All Wire Orientations
Scan 1.1
Scan 1.2
Scan 1.3
Scan 2.1
Scan 2.2
Scan 2.3
Scan 3.1
Scan 3.2
Scan 3.3
Scan 4.1
Scan 4.2
Scan 4.3
Scan 2.1-2.3
Scan 1.1-1.3
Scan 3.1-3.3
Scan 4.1-4.3
RF Effects
2011 National Electrical Code ®
requires detection and interrupt of arc faults in PV systems.
Sandia Research: Arc modeling and electrical propagation studies.
Arc detection using frequency content of the PV string
Industry responds by creating PV AFCI devices.
Sandia research helps industry make better products.
Industry works with Sandia to test AFCIs.
Jay Johnson 24 June, 2011 Slide 4/18
Why Test Arc Detection at Sandia National Laboratories?
Sandia National Labs is a resource for PV companies, technologies, and components.
• SNL has partnerships with inverter, module, BOS components, AFD, and AFCI manufacturers.
Distributed Energy Technologies Laboratory (DETL)
• Test bed for novel renewable energy technologies.
• Reconfigurable PV arrays with diverse portfolio of PV technologies: Different manufacturers, ages, and I-V
characteristics Range of connectors, DC disconnects, combiner
boxes, line lengths, and inverters. UL Subject 1699B does not cover all testing
cases or scenarios.• DETL can demonstrate AFCI robustness.
Distributed Energy Technologies Laboratory
Jay Johnson 24 June, 2011 Slide 5/18
Arc Fault Detection Challenges
Some AFCIs use the AC frequency content of the string for detection Two challenges involved with arc detection using a remote arc fault detector:
1. Missed or delayed detection due to arc frequency attenuation in PV components (e.g., modules, connectors, bypass diodes)
2. Nuisance tripping due to noise from electromagnetic coupling (crosstalk), inverter switching, and radio frequency (RF) effects
“Pink” AC noise Modules/connectors change frequency content
RF phenomena, crosstalk noise, antenna effects
Inverter switching noise
Jay Johnson 24 June, 2011 Slide 6/18
Arc Fault Experiments
Arc Fault Generator
Questions What is the influence of inverters on string noise? Are there frequency bands which are excited with an arc? Does crosstalk trip the AFCI? Do antenna effects and RF phenomenon influence detection? Does arc fault location change the arcing frequency content? Do DC/DC converters change the PV string AC spectrum?
DAQ System 10 MHz Current and Voltage
Time Series Data
PV String Testing Options at DETL
Basic Testing Setup
Jay Johnson 24 June, 2011 Slide 7/18
Simulated Arc Fault
Jay Johnson 24 June, 2011 Slide 8/18
String Noise Varies with Inverter Type, PV Module Technology, and Array Topology
120 Hz noise from the inverter compared to a
resistive load bank noise.
MPPT effect on current.
4 kW Inverter, 3 Strings of 2 540-W a-Si BIPV Modules
75 kW 3-phase Inverter, 8 Strings of 12 175-W a-Si Modules
3 kW Inverter, 4 Strings of 6 200-W c-Si Modules
20 kW 3-phase Inverter, 1 String of 21 90-W c-Si Modules
4.8 kW Inverter, 4 Strings of 6 175-W c-Si Modules
20 kW 3-phase Inverter, 1 String of 22 80-W c-Si Modules
Qualitative String Current Noise Comparison
Noi
se A
mpl
itude
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0Time (s)
Jay Johnson 24 June, 2011 Slide 9/18
String Noise in Frequency Domain
Switching Frequency for Inverter
120 Hz Noise
Single-Sided Amplitude Spectrum of String Current
Cur
rent
Noi
se A
mpl
itude
(dB
)
Red line is the average of the current noise for
each decade.
101 102 103 104 105 106
Frequency (Hz)
-20
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-60
-80
-100
-120
-140
-160
-180
-200
Jay Johnson 24 June, 2011 Slide 10/18
Testing Configurations
Baseline with an inverter.
Baseline without an inverter
Arc with an inverter.
Arc without an inverter
Jay Johnson 24 June, 2011 Slide 11/18
DC String Current during an Arc Fault
Arcs, inverter
Arcs, load bankNo arcs, inverter
Arc fault begins at 0 sec.
No arcs, load bank
DC String Current vs Time
Strin
g C
urre
nt (A
)
Time (s)
3.8
4.0
3.6
2.4
3.4
3.2
3.0
2.8
2.6
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8-0.2 -0.1
Jay Johnson 24 June, 2011 Slide 12/18
Arcs, inverter
Arcs, load bankNo arcs, inverter
No arcs, load bank
Arc fault begins at 0 sec.
DC String Voltage during an Arc Fault
DC String Voltage vs Time
Time (s)0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8-0.2 -0.1
285
290
280
350
275
370
365
360
355
Strin
g Vo
ltage
(V)
Jay Johnson 24 June, 2011 Slide 13/18
Arcs, inverter
No arcs, inverter
Arcs, load bank
No arcs, load bank
AC Arc Fault Frequencies on PV Strings
Single-Sided Amplitude Spectrum of String Current
Frequency (Hz)101 102 103 104 105 106
-140
-20
-40
-60
-80
-100
-120
-160
-180
-200
0
Cur
rent
Noi
se A
mpl
itude
(dB
)
Jay Johnson 24 June, 2011 Slide 14/18
Binned Arc Current and Voltage Frequencies
Arcs, inverter
No arcs, inverter
Arcs, no inverter
No arcs, no inverter
String Current Spectrum (Binned)
Frequency (Hz)
Cur
rent
Noi
se A
mpl
itude
(dB
) What’s the best way to differentiate arcing and non-arcing strings?
101 102 103 104 105 106
-20
-40
-60
-80
-100
-120
-30
-50
-70
-90
-110
Jay Johnson 24 June, 2011 Slide 15/18
Arc Fault Generation on Arrays
Baselines
Arc on String 3
Arc on String 2Arc on String 1
Same 3-phase inverter with 3 different strings:• 21 90-W c-Si modules, 22 80-W p-Si modules, 22 80-W c-Si modules
Single-Sided Amplitude Spectrum of String Current
Cur
rent
Noi
se A
mpl
itude
(dB
)
Hard to differentiate regionEasy to differentiate regionHard to differentiate region
101 102 103 104 105 106
-140
-20
-40
-60
-80
-100
-120
-160
-180
-200
Jay Johnson 24 June, 2011 Slide 16/18
Conclusions
2011 NEC requires DC arc fault circuit protection on photovoltaic systems with dc source circuits, dc output circuits, or both, on or penetrating a building operating at a PV system maximum system voltage of 80 volts or greater.
Sandia National Laboratories provides an excellent testing facility for arc fault detectors and arc fault circuit interrupters because of the diversity of PV technologies.
Experimental work with Eaton has revealed some avenues for robust detection as well as some arc fault detection challenges.
• Arcing can excite certain frequency bands above the baseline (non-arcing) levels.
• Inverters generate a lot of baseline noise across the spectrum, but especially at 120 Hz, switching frequencies and harmonics.
Additional experimentation is recommended to further understand arcing phenomenon and signal propagation in a broad range of PV systems.
Jay Johnson 24 June, 2011 Slide 17/18
Acknowledgements
DETL Technicians• Armando Fresquez• Mike Montoya• Nelson Opell
Engineering Assistance• Sigfredo Gonzalez
US Department of Energy Solar Energy Technologies Program
Questions?
Jay JohnsonSandia National LabsPhone: [email protected]
Charles LuebkeEaton CorporationPhone: [email protected]
Contact Information