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					Avionics Workshop
   Ottawa, Ontario, 2004
     Ahmed El Goueli
                            Avionics
               ARC FAULT CIRCUIT BREAKERS



The issue of aircraft wiring safety has received widespread attention in
recent years, highlighted by the unfortunate TWA 800 and Swissair 111
tragedies. As a result of these incidents and other concerns, the issue of
wiring safety has been taken up by OEMs, regulatory agencies, the
military, and is being addressed as part of the Aging Transport Systems
Rulemaking Advisory Committee (ATSRAC).




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                           Avionics
               ARC FAULT CIRCUIT BREAKERS


                 Protection Against Arc Fault Accident


���� Wire Selection
���� Wire Installation
���� Wire Maintenance
���� Arc Fault Circuit breaker




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                                  Avionics
                  ARC FAULT CIRCUIT BREAKERS

                                    Definition
Aircraft circuit breakers have historically been the best available protection for
aerospace wiring. These circuit interruption devices are used protect the aircraft
wiring from overheating or melting. During arcing faults these currents are often
small, short in duration and well below the overcurrent time protection curve
designed into these breakers.

An arc-fault circuit interrupter (AFCI) is a device intended to provide protection from
the effects of arc-faults by recognizing characteristics unique to arcing and by
functioning to de-energize the circuit when an arc-fault is detected




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ARC FAULT CIRCUIT BREAKERS




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                                          Avionics
                        ARC FAULT CIRCUIT BREAKERS

                                    How it works ???
AFCI technology monitors the electrical circuit for arcing events that are indicative of potentially unsafe
wiring conditions and could result in fires or loss of electrical circuit functionality.

The AFCB trips in about five milliseconds, greatly reducing the chance of damaging the rest of the
surrounding wiring, other equipment and structure.

Laboratory tests have shown that AFCI breakers detect faults and trip faster than aircraft circuit
breakers and are significantly faster at detecting arcing faults in aircraft wiring.




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                ARC FAULT CIRCUIT BREAKERS

                                        DESIGN
A robust AFCI algorithm should not rely on current level to determine an arcing event, but should
distinguish the arcing event based on the arcing content of the signal

The AFCI must be designed such that:

1.To distinguish such a wide variety of normal steady state and transient load characteristics
2.To recognize normal steady state and transient load conditions
3.Be packaged in an integral device and can be interchangeably installed with existing CB.




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ARC FAULT CIRCUIT BREAKERS




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              ARC FAULT CIRCUIT BREAKERS



                          DESIGN

There are a number of undesirable arcing conditions that have
been identified that the arc fault detection algorithm should be
required to protect against. These arcing conditions can be
manifested in arcing between parallel conductors, to ground,
or in series along the conductor.



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                                        Avionics
                      ARC FAULT CIRCUIT BREAKERS

                                          Parallel Arcs

Parallel arcing occurs when there is a arc between two wires or wire-to-frame and the current is limited
by the impedance of the voltage source, the wire, and the arc. Parallel arcing is generally more
hazardous than series arcing. The energy released in the arc is much higher with temperatures in
excess of 10,000 Deg. F. This causes pyrolyzation or charring of the insulation, creating conductive
carbon paths and ejecting hot metal that is likely to encounter flammable materials.


                                           Series Arcs

Series arcing may begin with corrosion in pin-socket connections or loose connections in series with
the electrical loads. Loose terminal lugs, misarranged or cross-threaded electrical plugs, broken
conductor strands inside a wire are also possible sources. The amount of power from a series arc is far
less than in a parallel fault. Series arcing is particularly treacherous because the arc current remains
well below the trip curve of the Mil-Spec aircraft breaker. These arcs cause load voltage drops and
heating of the wire, pin and sockets, or terminal lugs.This heating can lead to component failure and
ignition source.


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ARC FAULT CIRCUIT BREAKERS




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         ARC FAULT CIRCUIT BREAKERS


                  Proof of Concept

1.   Loose Terminal Test.

2.   Guillotine or Point Contact Test.

3.   Carbonized Path Test.

4.   Wet Arc or Salt Water Drip Test.


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                                 Avionics
            ARC FAULT CIRCUIT BREAKERS


                                            Tripped AFCI Breaker with
                                            indication of arcing fault




Tripped AFCI Breaker with
indication of thermal overload




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ARC FAULT CIRCUIT BREAKERS




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                             Avionics
            ARC FAULT CIRCUIT BREAKERS


                      ADVANTAGES OF AFCB


1.   AFCBs provide a simple means for mitigating the effects of electrical arcing
     before the arc develops into a serious condition, preventing potentially
     catastrophic damage to electrical wire bundles.

2.   AFCBs will limit the energy expended by the arc fault thereby reducing the
     potential to ignite surrounding materials (i.e., wire insulation, lint, cleaning
     fluids, etc.) and the associated smoke and fire that can occur.

3.   A tripped AFCB will identify on which wire the fault is located.

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                           Avionics
           ARC FAULT CIRCUIT BREAKERS

                               CONCERNS

1.   Present AFCB prototypes do not provide a means for monitoring the
     performance of the AFCB functional status. In the absence of an active status
     indication, some AFCB surveillance programs may be necessary to provide
     assurance that the AFCBs are fully functional.

2.   The rate of AFCB tripping versus thermal circuit breakers. Upon installation of
     AFCBs, the rate of AFCB trips will be greater than that of the thermal breakers
     being replaced.

3.   The problem of determining the location of the arc fault along the length of the
     circuit.


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                                    Avionics
                 ARC FAULT CIRCUIT BREAKERS

                                           Summary
While further technology development is ongoing for AC and DC applications. AFCI technology
for aircraft requires a robust algorithm that provides:
1.Fast response to true arcing events
2.Does not result in nuisance trips
3.Ability to discriminate between normal and transient load signatures and arcing events
4.Ability to sense arcing events in the presence of masking loads
5.Immunity to filters, EMI, cross-talk, and other circuit “noise”
6.Low level arc sensitivity
There are numerous issues that need to be addressed to satisfy the wiring system application
and protection requirements on commercial and military aircraft. Moreover, the detection levels
and performance requirements must be such that these new products provide a truly enhanced
circuit protection function in the aircraft wiring system.



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                              Avionics
                ARC FAULT CIRCUIT BREAKERS

                     Transport Canada Position

Awaiting maturity of the product development, specific projects in Canada utilizing
AFCBs are being addressed by issue papers. The IPs provide clarification of the
criteria and TC policy for means of compliance expected with the applicable
regulations.


                         Upcoming Milestones

•SAE Committee is developing an industry standard for “minimum operating
specification for AFCBs.”
• FAA is developing associated TSO and advisory circular in parallel with the SAE
activity.
• TC will adopt the FAA policy or issue an AMA if needed.
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ARC FAULT CIRCUIT BREAKERS


        Questions ?




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