Resistive fault sectionalization

• US 4,399,402 A
• Filed: 08/31/1981
• Issued: 08/16/1983
• Est. Priority Date: 08/31/1981
• Status: Expired due to Term

• Current Assignee: Bell Telephone Laboratories, Inc. (Nokia Corporation)
• Original Assignee: Bell Telephone Laboratories, Inc. (Nokia Corporation)
• Inventors: Pelletier, James A.
• Primary Examiner(s): Krawczewicz, Stanley T.
• Assistant Examiner(s): Solis, Jose M.
• Application Number:
  US06/298,074
• Time in Patent Office: 715 Days
• Field of Search: 324/51, 324/52, 179/175.3 R, 179/175.3 F
• US Class Current: 324/525
• CPC Class Codes: G01R 31/083 in cables, e.g. underground
• CPC Class Codes: G01R 31/50 Testing of electric apparatus, lines, cables or components for short-circuits, continuity, leakage current or incorrect line connections testing of sparking plugs H01T13/58
• CPC Class Codes: G01R 31/52 Testing for short-circuits, leakage current or ground faults

Abstract

A methodology, and associated circuitry, for locating a resistive shunt fault coupling the cable shield and the conductors of the cable pair under test comprises the steps of: (i) measuring the open-circuited DC resistance (A₁ and A₂) of the pair from test locations (A and B) which straddle the fault; (ii) measuring the short-circuited DC resistance (A₃) of the pair from one of the test points (A or B); and (iii) evaluating the resistance of one conductor of the pair between the fault and the location of the short circuit measurement according to a predetermined quadratic expression involving the three measured quantities. Sensitivity of the measurement technique is reduced by adding a resistor in series with said pair, at either location A or B, so that A₂ is substantially equal to A₁.

Claims

1. A method for testing a cable pair (TIP,RING) to locate a shunt resistance fault (R_F) between first (A) and second (B) test positions by determining the conductor (TIP or RING) resistance (R_X) between said fault and said second test position, said method

CHARACTERIZED BY THE STEPS OF

measuring the DC resistance (A₁) of said pair at said first test position with said pair open-circuited at said second test position,

measuring the DC resistance (A₂) of said pair at said second test position with said pair open-circuited at said first test position,

measuring the DC resistance (A₃) of said pair at said second test position with said pair short-circuited at said first test position, and

determining the value of said resistance (R_X) from the expression

2. A method for testing a cable pair (TIP,RING) to locate a shunt resistance fault (R_F) between first (A) and second (B) test positions by determining the conductor (TIP or RING) resistance (R_X) between said fault and said second test position, said method

CHARACTERIZED BY THE STEPS OF

measuring the DC resistance (A₁) of said pair at said first test position with said pair open-circuited at said second test position,

adding a preselected resistance (±

R) in series with one conductor (TIP or RING) of said pair to form a series combination,

measuring the DC resistance (A₂) of said series combination at said second test position with said pair open-circuited at said first test position,

measuring the DC resistance (A₃) of said series combination at said second test position with said pair short-circuited at said first test position, and

determining the value of said resistance (R_X) from the expression

space="preserve" listing-type="equation">(R.sub.X ±

R).sup.2 -A.sub.2 (R.sub.X ±

R)+(A.sub.1 /4) (A.sub.3 -A.sub.2)+(A.sub.2 /2).sup.2 =0.

3. The method as recited in claim 2 further comprising the step of selecting said resistance (±

R) so that A₂ essentially equals A₁.

4. Testing apparatus for locating a pair fault (R_F) between first (A) and second (B) test positions by determining the conductor (TIP or RING) resistance (R_X) between said fault and said second test location, said apparatus

CHARACTERIZED BY

first means at said first location to sequentially configure said pair (i) for measuring the DC resistance (A₁), (ii) by open-circuiting and (iii) by short-circuiting said pair, respectively, and

second means at said second location, operating simultaneously with said first means, to configure said pair (i) by open-circuiting said pair, (ii) for measuring the DC resistance (A₂), and (iii) for measuring the DC resistance (A₃), respectively, of said pair,

wherein said resistance (R_X) is a solution to the quadratic expression

5. Testing apparatus for locating a pair fault (R_F) between first (A) and second (B) test locations by determining the conductor (TIP or RING) resistance (R_X) between said fault and said second test location, said apparatus

CHARACTERIZED BY

first means at said first location to sequentially configure said pair (i) for measuring the DC resistance (A₁), by (ii) open-circuiting and (iii) by short-circuiting said pair, respectively, and

second means at said second location, operating simultaneously with said first means, to configure said pair (i) by open-circuiting said pair, (ii) by adding a preselected resistor (±

R) in series with one conductor of said pair and measuring the DC resistance (A₂) of the series combination, and (iii) by measuring the DC resistance (A₃) of said combination,

wherein said resistance (R_X) is a solution to the quadratic expression

space="preserve" listing-type="equation">(R.sub.X ±

R).sup.2 -A.sub.2 (R.sub.X ±

R)+(A.sub.1 /4) (A.sub.3 -A.sub.2)+(A.sub.2 /2).sup.2 -0.

6. The apparatus as recited in claim 5 wherein said resistor (±

R) is chosen so that A₂ essentially equals A₁.

7. Wire-pair apparatus for testing a resistive fault (R_F) located between first (A) and second (B) test locations and for determining the resistance (R_X) of one wire (TIP or RING) between said fault and said second test location, said apparatus

CHARACTERIZED BY

first means at said first location having three sequential modes of operation including:

a first mode for measuring the DC resistance (A₁) of said pair;

a second mode for disconnecting said first means from said pair; and

a third mode for shorting said pair, and

second means at said second location operating in one-to-one correspondence to said modes for;

disconnecting said second means from said pair during said first mode;

measuring the DC resistance (A₂) of said pair during said second mode; and

measuring the DC resistance (A₃) of said pair during said third mode,

wherein said resistance (R_X) is a solution to the quadratic expression

space="preserve" listing-type="equation">R.sub.X.sup.2 -A.sub.2 R.sub.X +(A.sub.1 /4) (A.sub.3 -A.sub.2)+(A.sub.2 /2).sup.2 =0.