Differential arc reflectometry

• US 5,083,086 A
• Filed: 07/12/1990
• Issued: 01/21/1992
• Est. Priority Date: 07/12/1990
• Status: Expired due to Fees

• Current Assignee: James G. Biddle Company
• Original Assignee: James G. Biddle Company
• Inventors: Steiner, James P.
• Primary Examiner(s): Wieder, Kenneth A.
• Assistant Examiner(s): Solis, Jose M.
• Application Number:
  US07/552,251
• Time in Patent Office: 558 Days
• Field of Search: 324/533, 324/534, 324/536, 324/644, 379/26
• US Class Current: 324/533
• CPC Class Codes: G01R 31/11 using pulse reflection methods

Abstract

Location of a fault in electrical conductors from a terminal position which may be remote from the fault using at least a broad band pulse generator to generate a pulse at a terminal position. It also uses a voltage source at the terminal position capable of inducing a change of impedance at the fault and time measuring means also at the terminal position. The method involves generating a first pulse at the terminal position which is propagated down the conductor and reflected back to the terminal position from various impedance discontinuities, including the impedance discontinuity of the fault, if present. The pattern of reflections from points along the conductor up to the fault resulting from the first pulse are recorded. Then sufficient voltage is applied to the cable to induce a change in impedance at the fault. Simultaneously a second pulse similar to the first is generated at the terminal position and reflected back from the various impedance discontinuities, including the modified impedance discontinuity at the fault. The reflections of the first pulse are then substracted from the reflections of the second pulse leaving the pulse reflected from the fault. The location of the fault is then determined from the time taken from initiation to reflection of the pulse to the terminal position.

Claims

1. The method of determining the location of a fault in electrical conductors from a terminal position which may be remote from the fault using at least a broadband pulse generator to generate a pulse at the terminal position, a voltage source at the terminal position capable of inducing a change of impedance at the fault and time measuring means also at the terminal position, comprising:

generating a first pulse at the terminal position to be propagated down the conductor and reflected back to the terminal position from various impedance discontinuities, including the impedance discontinuity at the fault, if present;

recording the pattern of reflections from points along the conductor up to the fault, resulting from the first pulse;

applying sufficient voltage to the cable to induce a change in impedance at the fault and simultaneously generating a second pulse similar to the first at the terminal position to be propagated down the conductor and reflected back to the terminal position from the various impedance discontinuities up to the fault and from the modified impedance discontinuity at the fault;

subtracting the reflections from the first pulse from the reflections of the second pulse; and

determining from the remaining major reflections, the location of the fault.

2. The method of claim 1 in which the pattern of reflections from points along the conductor from the second pulse are also recorded.

3. Apparatus for determining the location of a fault in electrical conductors from a terminal position which may be remote from the fault comprising:

a broadband pulse generator to generator a pulse at the terminal position;

a voltage source capable of producing at least a momentary change of impedance at the fault site;

means to store a reflected signal generated by use of the pulse generator without application of voltage to induce an impedance change at the fault;

means for eliminating the voltage applied;

means to store a similar signal and means to compare and subtract the signal without the impedance changing voltage applied from the signal with the impedance change at the fault generated by the impedance changing voltage;

timing means to initiate timing by a pulse generated by the pulse generator and to terminate timing by a signal left by the difference between the two functions to determine the timing of the round trip delay to the fault; and

means to calculate from the time the distance to the fault.

4. The apparatus of claim 3 in which a filter is used to separate the voltage used to induce the change of impedance from the broadband time domain reflectometry pulse;

and

a digitally implemented time domain reflectometer are employed.

5. Apparatus for determining the location of a fault in electrical conductors from a terminal position which may be remote from the fault comprising:

a signal generator to generate the time domain reflectometry signal at the terminal position;

a means to determine a function which has the mathematical property of superposition and is representative of the time delay between the reflections;

a voltage source of producing at least a momentary change of impedance at the fault site;

means to store the function, representative of the time delay between reflections, without application of the impedance changing voltage;

means for eliminating the voltage applied;

means to store a similar function, representative of the time delay between reflections, and means to compare and subtract the representative function, without the impedance changing voltage applied, from the function, representative of the time delay between reflections, with the impedance changing voltage applied;

timing means to determine the time between the signal applied at the terminal position and the function left by the difference between the two functions to determine the round-trip delay time to the fault; and

means to calculate from the round-trip delay time the distance to the fault.