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. Jay Johnson, [email protected] Ward Bower, [email protected] Sandia National Laboratories Albuquerque, NM October 21, 2011 Solar Power International Conference Dallas, TX Codes and Standards for Photovoltaic DC Arc-Fault Detection
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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.
Jay Johnson, [email protected]
Ward Bower, [email protected]
Sandia National Laboratories
Albuquerque, NM
October 21, 2011
Solar Power International Conference
Dallas, TX
Codes and Standards for Photovoltaic DC Arc-Fault Detection
Presentation Outline
• PV Arc-Fault Classifications
• Arc-Fault Codes and Standards
• Sandia National Labs Research
• Potential for Parallel Arc-Fault Protection
• Arc-Free Future
PV Arc-Fault Detection Codes
3 Types of Arc-Faults in PV Systems
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Arc-faults in PV
systems cause fires.
Series Arc-Fault:
NEC 690.11
Parallel Arc-Fault:
Not in the NEC Ground Arc-Fault:
NEC 690.5
690.11 Arc-Fault Circuit Protection (direct current): 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, shall be protected by a listed (dc) arc-fault circuit interrupter, PV type, or other system components listed to provide equivalent protection. The PV arc-fault protection means shall comply with the following requirements:
(1) The system shall detect and interrupt arcing faults resulting from a failure in the intended continuity of a conductor, connection, module, or other system component in the dc PV source and output circuits.
(2) The system shall disable or disconnect one of the following: a. Inverters or charge controllers connected to the fault circuit when the fault is detected. b. System components within the arcing circuit.
(3) The system shall require that the disabled or disconnected equipment be manually restarted. (4) The system shall have an enunciator that provides a visual indication that the circuit interrupter has operated. This indication
shall not reset automatically.
2011 National
Electrical Code ®
requires PV arc-
fault protection.
Arc-faults in PV
systems cause fires.
PV Arc-Fault Detection Codes
1. Arcing can occur at voltages well below 80 volts. Should this value be reduced to a level where
there is certainty that an arc will not initiate?
2. Some members of the industry believe the manual restart is overly prescriptive. Are there
situations where automated restarts could be permissible?
2011 National
Electrical Code ®
requires PV arc-
fault protection.
Arc-faults in PV
systems cause fires.
UL 1699B is
created to list
arc-fault
protection
devices. SUBJECT 1699B
OUTLINE OF INVESTIGATION
FOR
PHOTOVOLTAIC (PV) DC
ARC-FAULT CIRCUIT
PROTECTION
COPYRIGHT © 2011
UNDERWRITERS
LABORATORIES, INC.
UL Subject 1699B Test Sequence
• Humidity
• Leakage
• Voltage Surge
• Environmental Sequence
• Arc Fault Detection
• Unwanted Tripping
• Inhibition
• Temperature
• Overvoltage
• Overload
• Endurance
• Dielectric Voltage Withstand
• Abnormal
• Short Circuit
• Corrosion test
• Crushing
• Strain Relief
• Mechanical
• Resistance to Environmental Noise
• Electrostatic Discharge
• Radiated EMI
• Fast Transients
• Voltage Surge
• Induced RF Fields
• Voltage Dips
• Surge Current
• Abnormal Voltage
PV Arc-Fault Detection Codes
Listing standards must ensure quick detection without nuisance tripping in situations with:
- Noisy inverters
- Lightning, large radio signal amplitudes, and other RF noise
- Arcs from DC disconnects and other contactor open/closing operations
2011 National
Electrical Code ®
requires PV arc-
fault protection.
Arc-faults in PV
systems cause fires. Industry responds by
creating PV AFCI
devices.
UL 1699B is
created to list
arc-fault
protection
devices. SUBJECT 1699B
OUTLINE OF INVESTIGATION
FOR
PHOTOVOLTAIC (PV) DC
ARC-FAULT CIRCUIT
PROTECTION
COPYRIGHT © 2011
UNDERWRITERS
LABORATORIES, INC.
PV Arc-Fault Detection Codes
2011 National
Electrical Code ®
requires PV arc-
fault protection.
Arc-faults in PV
systems cause fires. Industry responds by
creating PV AFCI
devices.
UL 1699B is
created to list
arc-fault
protection
devices. SUBJECT 1699B
OUTLINE OF INVESTIGATION
FOR
PHOTOVOLTAIC (PV) DC
ARC-FAULT CIRCUIT
PROTECTION
COPYRIGHT © 2011
UNDERWRITERS
LABORATORIES, INC.
Arc-fault 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
nit
ud
e (
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
Sandia Research: Arc modeling and electrical propagation studies.
Sandia/Industry
Collaborations
PV Arc-Fault Detection Codes
Arc detection using frequency
content of the PV string
Parallel Arc-Fault Detection • Often AFCIs use the AC frequency content of the string for detection
– Parallel and series arcing frequency are (supposedly) not differentiable – Opening the circuit makes parallel arcs worse
• One solution: guess-and-check – If there’s an arc, assume it’s a series arc and open the circuit. If arcing frequencies still
exist, short the PV.
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Series Arc-Fault Series Arc-Fault Extinguished
Parallel Arc-Fault Parallel Arc-Fault Intensifies Parallel Arc-Fault Extinguished A
FC
I R
ech
eck
AF
CI R
ech
eck
How fast can this be done? Will series+parallel AFCIs meet the current 1699B requirements?
Moving Toward an Arc-Free/Fire-Free Future for PV
• Need Codes and Standards for Series, Parallel, and Ground Faults – Parallel arc-fault detection must be addressed to prevent all PV-initiated
fires
• Tools to Determine Arc-Fault Location – Once the AFCI is tripped how can the faulty component be located?
• PV DC Arc Mitigation – Design smart PV systems and materials that mitigate arcing
• PV System Prognostics – Develop tools or passive indicators to report the health of PV systems
Acknowledgements
• Sandia Engineering Support – Sigifredo Gonzalez – Jennifer Granata – Michael Quintana
• UL
– David Dini – Tim Zgonena
• US Department of Energy Solar Energy Technologies Program
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