Method and Apparatus for Locating a Parallel Arc Fault

Abstract

Methods to determine the location of an arc fault include a first method utilizing the inherent resistance per unit length of the wire. A second and a third method utilize an inherent inductance per unit length of the wire. The second method derives the inherent inductance from the output voltage and a rate of current rise. The third method derives the inherent inductance from a resonant frequency of an oscillating current. The information is useful to locate a fault emanating from a wire member of a wiring harness used to distribute power about an aircraft.

What is claimed is: 
     
         1 . A method to measure a distance to an arc emanating from a wire having a voltage source and electronic circuit breaker at a first end thereof and a load at a second end thereof, comprising the steps of:
 obtaining an output voltage, V 0 , of said voltage source and a peak current, I arc(peak) , of said circuit;   calculating a resistance of said wire up to said arc from:
     R   wires   =V   0   /I   arc(peak) ; and 
   utilizing an inherent resistance per unit of length of said wire to determine a distance from said voltage source to said arc.   
     
     
         2 . The method of  claim 1  wherein said wire is bundled in a wiring harness having a plurality of parallel running wires and said wiring harness is installed on an aircraft. 
     
     
         3 . The method of  claim 2  wherein said arc extends from said wire to a second wire and R wires  is the sum of the resistance of said wire and said second wire from said voltage source to said arc. 
     
     
         4 . The method of  claim 2  including calculating a Critical Length of said wire beyond which a short circuit current drops below a 10x rating for said electronic circuit breaker whereby if said electronic circuit breaker trips, then said distance to said arc is less than said Critical Length. 
     
     
         5 . The method of  claim 2  wherein said arc extends from said wire to an airframe of said aircraft and R wires  is the resistance of said wire from said voltage source to said arc. 
     
     
         6 . The method of  claim 1 , wherein V o  is obtained by measuring the output voltage of the electronic circuit breaker. 
     
     
         7 . The method of  claim 1 , further comprising estimating an error in said distance determination, by
 assuming a value for resistance of said arc R arc ; and   calculating the error as R arc /R wires , the error being expressed as a percentage.   
     
     
         8 . The method of  claim 1 , further comprising estimating an error in said distance determination, by
 estimating an arc current I arc ;   assuming a value for resistance of said arc R arc ; and   calculating the error as I arc *R arc /V 0 , the error being expressed as a percentage.   
     
     
         9 . The method of  claim 8 , further comprising using the value of I arc(peak)  for I arc  to estimate a minimum error. 
     
     
         10 . The method of  claim 8 , further comprising
 assuming R arc =0; and   calculating a critical length of said wire in accordance with the wire gauge and a rating value for said circuit breaker.   
     
     
         11 . The method of  claim 10 , wherein the critical length for said wire gauge is the length for which a hard fault results in an I 2 t trip at the circuit breaker.