US3781665A
Expired / Lapsed
US
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Cable fault location indicator
Assignee: Electricity Council
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Filing: 1971-07-08
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Granted: 1973-12-25
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Expires: 1991-07-08
Abstract
Abstract A method of, and apparatus for, locating a fault in an underground electrical power cable. The cable is excited to induce resonance between a fault and the end of the cable at which an indicator, comprising a sensor and processing circuitry, is attached. The time interval between successive waves or groups of waves, measured between the zero points of the waves, is used to gate a clock pulse generator into a counter having a visual display. The frequency of the clock pulse generator is arranged such that the reading on the counter is the distance from the indicator to the fault, expressed in metres, and the clock pulse generator is provided, with compensation for the frequency dependence of the velocity of propagation in the cable. Calibration of the indicator may be internal with respect to theoretical value for the velocity of propagation, or on-site, with respect to the actual velocity of propagation.
Inventors
- 👤 P Gale
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-30 14:55
CPC Classifications
G; G01; G01R; G01R31/00; G01R31/08
Claims Analysis
Total Claims: 14
Claim 1
Independent Claim
186 words
A method of locating a fault in an electrical cable comprising the steps of breaking down the fault by applying at one end of the cable, a substantially D.C. voltage between two conductive elements of the cable between which the fault exists; receiving at the opposite end of the cable the oscillatory waveform established between said two conductive elements as a result of successive reflections at the fault, and at said opposite end, of a travelling electromagnetic wave generated by the breakdown of the fault; detecting and discarding n, where n is a positive integer, successive half-cycles of the oscillatory waveform starting from the first zero-crossing of the waveform; detecting the occurrence of the next m successive cycles thereafter; obtaining a measure of the time interval, T, of said m successive cycles, where m is a positive integer; and processing said time interval T in accordance with the expression 1 v.T/4m, where v is a predetermined value for the velocity of electromagnetic waves in the cable, in order to derive a value for the distance, 1, of the fault from said opposite end of the cable.
Claim 2
Independent Claim
186 words
A method of locating a fault in an electrical cable comprising the steps of breaking down the fault by applying at one end of the cable, a substantially D.C. voltage between two conductive elements of the cable between which the fault exists; receiving at the opposite end of the cable the oscillatory waveform established between said two conductive elements as a result of successive reflections at the fault, and at said opposite end, of a travelling electromagnetic wave generated by the breakdown of the fault; detecting and discarding n, where n is a positive integer, successive half-cycles of the oscillatory waveform starting from the first zero-crossing of the waveform; detecting the occurrence of the next m successive cycles thereafter; obtaining a measure of the time interval, T, of said m successive cycles, where m is a positive integer; and processing said time interval T in accordance with the expression 1 v.T/4m, where v is a predetermined value for the velocity of electromagnetic waves in the cable, in order to derive a value for the distance, 1, of the fault from said opposite end of the cable.
Claim 3
Dependent Claim
67 words
A method as recited in claim 1 wherein the processing step is performed by gating a clock pulse generator into a counter for the period T, and, for compensating for a known frequency dependence of the velocity of propagation of electromagnetic waves in the cable, including the further step of reducing the frequency of the generator in a predetermined manner from the start of the gating period.
Claim 4
Independent Claim
212 words
An apparatus for locating a fault in an electrical cable, comprising means for generating and applying, at one end of the cable, a substantially D.C. voltage between two conductive elements of the cable between which the fault exists, in order to break down the fault; signal detecting means connectible, at the opposite end of the cable, between the two conductive elements, and providing an output signal corresponding substantially to the zero crossings of the oscillatory waveform established between said two conductive elements as a result of successive reflections at the fault of a travelling electromagnetic wave generated by the break down of the fault; signal processing means responsive to said output signal and including means for detecting and discarding n half-cycles of the oscillatory waveform, where n is a positive integer, starting from the first zero-crossing of the waveform, means detecting the occurrence of the next m successive Cycles, means for obtaining a measure of the time interval, T, of said m successive cycles, where m is a positive integer, and means for deriving a value for the distance, 1, of the fault from said opposite end of the cable in accordance with the expression l v.T/4m, where v is a predetermined value for the velocity of electromagnetic waves in the cable.
Claim 5
Independent Claim
212 words
An apparatus for locating a fault in an electrical cable, comprising means for generating and applying, at one end of the cable, a substantially D.C. voltage between two conductive elements of the cable between which the fault exists, in order to break down the fault; signal detecting means connectible, at the opposite end of the cable, between the two conductive elements, and providing an output signal corresponding substantially to the zero crossings of the oscillatory waveform established between said two conductive elements as a result of successive reflections at the fault of a travelling electromagnetic wave generated by the break down of the fault; signal processing means responsive to said output signal and including means for detecting and discarding n half-cycles of the oscillatory waveform, where n is a positive integer, starting from the first zero-crossing of the waveform, means detecting the occurrence of the next m successive Cycles, means for obtaining a measure of the time interval, T, of said m successive cycles, where m is a positive integer, and means for deriving a value for the distance, 1, of the fault from said opposite end of the cable in accordance with the expression l v.T/4m, where v is a predetermined value for the velocity of electromagnetic waves in the cable.
Claim 6
Dependent Claim
114 words
Apparatus as recited in claim 3 wherein the means for deriving a value for the distance l includes a clock pulse generator having a frequency of v/4m, where v is expressed in a convenient unit of length, a digital counter and display, gating means gatably connecting the generator to the digital counter, and wherein the means for obtaining a measure of the time interval T provides a gating pulse for controlling said gating means to connect the generator to the digital counter for a period equal to said time interval T whereby the number of clock pulses accumulated by the digital counter and displayed on the display is numerically equal to the distance l.
Claim 7
Dependent Claim
110 words
Apparatus as recited in claim 4 wherein the counting means includes a binary divider having a plurality of stages for counting the cycles of the oscillatory waveform, and wherein the means for obtaining a measure of the time interval T includes a bistable latch and an AND gate, the output from the appropriate divider stage being fed to said bistable latch and to said AND gate, and the false output of said bistable latch also being fed to said AND gate, the output of said AND gate being said gating pulse, which gating pulse corresponds to the groups of cycles n 2p-1, m 2p, where p is a positive integer.
Claim 8
Dependent Claim
139 words
Apparatus as recited in claim 4 wherein there is provided internal calibration means for calibrating the signal processing means with respect to the predetermined value of the velocity of propagation of electromagnetic waves in the cable, which internal calibration means comprises a controlled oscillator connectible to the input of said signal detecting means, and having a predetermined frequency, and means for producing a calibration gating pulse for connecting said generator to said digital counter, the calibration gating pulse corresponding to 4m X 10p, where p is 0, 1, 2, etc., multiplied by the time unit in which said velocity of propagation is expressed, the frequency of said generator being adjustable such that the number of clock pulses accumulated by the digital counter during the calibration gating pulse can be made substantially equal to 10p times said velocity of propagation.
Claim 9
Dependent Claim
136 words
Apparatus as recited in claim 4 wherein the means for generating and applying the substantially D.C. voltage comprises a capacitor, means for charging the capacitor to a high D.C. potential, and means for connecting the capacitor between two conductive elements of a cable, and including, for calibrating the processing means with respect to the actual velocity of propagation of electromagnetic waves in the cable, capacitor discharge means connectible between two conductive elements of the cable between which a fault does not exist, and also connectible across the capacitor such that the capacitor discharge initiates an oscillatory waveform in the cable, and wherein the clock pulse generator is adjustable so that with the signal detecting means connected between these last-mentioned conductive elements, the display can be made to indicate the recorded length of these last-mentioned conductive elements.
Claim 10
Dependent Claim
34 words
An apparatus as recited in claim 7 wherein said capacitor discharge means comprises a spark-gap connected in series with a current limiting resistor, the spark-gap having a break down voltage of a few kilovolts.
Claim 11
Dependent Claim
56 words
An apparatus as recited in claim 4 wherein the signal processing means includes frequency controlling means connectible to said clock pulse generator during said gating pulse to reduce the Frequency of the generator in a predetermined manner in order to compensate for the frequency dependence of the velocity of propagation of electromagnetic waves in the cable.
Claim 12
Dependent Claim
26 words
An apparatus as recited in claim 9 wherein the generator comprises a voltage controlled oscillator and the frequency controlling means comprises a voltage ramp producing circuit.
Claim 13
Dependent Claim
116 words
An apparatus as recited in claim 3 wherein the means for deriving a value for the distance, 1, includes a counter, a clock pulse generator having a controllable pulse repetition frequency, means for gating the pulses from the generator into the counter for a period T; and wherein there is provided frequency controlling means connectible to the generator during the gating period for reducing the frequency of the generator in a predetermined manner in order to compensate for the frequency dependence of the velocity of propagation of electromagnetic waves in the cable, such that the number of pulses accumulated in the counter correspond to the distance from the fault to said opposite end of the cable.
Claim 14
Dependent Claim
25 words
Apparatus as recited in claim 11 wherein the generator comprises a voltage controlled oscillator and the frequency controlling means comprises a voltage ramp producing circuit.
References Cited (Backward Citations)
No citation records indexed.
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1976-12-24 | 1977-06-25 | 1977-12-25 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1980-12-24 | 1981-06-25 | 1981-12-25 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1984-12-24 | 1985-06-25 | 1985-12-25 | $7700.00 | Window Closed / Lapsed |