Avionics Workshop Ottawa, Ontario, 2004 Ahmed El Goueli

2 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).

3 Avionics ARC FAULT CIRCUIT BREAKERS Protection Against Arc Fault Accident Wire Selection Wire Installation Wire Maintenance Arc Fault Circuit breaker

4 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

5 Avionics ARC FAULT CIRCUIT BREAKERS

6 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.

7 Avionics 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.

8 Avionics ARC FAULT CIRCUIT BREAKERS

9 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.

10 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.

11 Avionics ARC FAULT CIRCUIT BREAKERS

12 Avionics ARC FAULT CIRCUIT BREAKERS

13 Avionics 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.

14 Avionics ARC FAULT CIRCUIT BREAKERS Tripped AFCI Breaker with indication of thermal overload Tripped AFCI Breaker with indication of arcing fault

15 Avionics ARC FAULT CIRCUIT BREAKERS

16 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.

17 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.

18 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.

19 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.

20 Avionics ARC FAULT CIRCUIT BREAKERS Questions ?