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 of said source, V source , and a rate of current rise as a function of time, di/dt;   calculating an inductance of said wire, L wires  up to said arc from:
     L   wire   =V   source /( di/dt ); and 
   utilizing an inherent inductance 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 di is a function of V source  and R arc  where R arc  is the resistance of said arc. 
     
     
         4 . The method of  claim 2 , wherein di is a function of V source  and R Σ  where R Σ  is the sum of the resistances of said arc, said voltage source, said electronic circuit breaker and said wire. 
     
     
         5 . The method of  claim 1 , wherein the inherent inductance K per unit length of said wire is in accordance with a type and a gauge of the wire, and said distance D from said voltage source to said arc is determined from
     D= ½( L   wires   /k ).
   
     
     
         6 . The method of  claim 1  wherein V source  is approximated as a measured output voltage V 0  of the circuit breaker. 
     
     
         7 . The method of  claim 3 , wherein an initial condition for the current is given by a steady state current L load  from the voltage source into the load and the current i(t) is determined from
     i ( t )=( V   source   /R   arc )+( I   load −( V   source   /R   arc ))exp−( R   arc   /L   wires )* t.  
   
     
     
         8 . The method of  claim 7 , wherein a voltage drop across the arc given by i(t)R arc  is characterized as an error term in the calculation of the inductance of said wire. 
     
     
         9 . The method of  claim 8 , 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 −(i(t)R arc )/V source , the error being expressed as a percentage.   
     
     
         10 . The method of  claim 8 , 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 −(i(t)R Σ )/V source , the error being expressed as a percentage, where R Σ  is the sum of the resistances of said arc, said voltage source, said electronic circuit breaker and said wire.