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WO1990011533A2 - Detection de defauts dans des cables - Google Patents

Detection de defauts dans des cables Download PDF

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Publication number
WO1990011533A2
WO1990011533A2 PCT/GB1990/000442 GB9000442W WO9011533A2 WO 1990011533 A2 WO1990011533 A2 WO 1990011533A2 GB 9000442 W GB9000442 W GB 9000442W WO 9011533 A2 WO9011533 A2 WO 9011533A2
Authority
WO
WIPO (PCT)
Prior art keywords
resistance
sheath
ground
fault
cable
Prior art date
Application number
PCT/GB1990/000442
Other languages
English (en)
Other versions
WO1990011533A3 (fr
Inventor
Nicholas James Frost
Richard William Fling
Original Assignee
Radiodetection Limited
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Radiodetection Limited filed Critical Radiodetection Limited
Publication of WO1990011533A2 publication Critical patent/WO1990011533A2/fr
Publication of WO1990011533A3 publication Critical patent/WO1990011533A3/fr

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Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
    • G01R31/50—Testing of electric apparatus, lines, cables or components for short-circuits, continuity, leakage current or incorrect line connections
    • G01R31/58—Testing of lines, cables or conductors

Definitions

  • the present invention relates to the detection of faults in cables.
  • the optical fibre is usually encased in armouring in the form of a metal helix, and the whole is encased in plastics material, nevertheless physical damage to the optical fibre in the cable sometimes occurs.
  • gophers chew the cable and they are able to bite through the armouring to the core of the cable. This alters the optical properties of the optical fibre in the cable (even assuming that the gopher does not break the optical fibre itself), and can render the cable unserviceable.
  • the first aspect of the present invention proposes that the signal applied to the sheath be a low frequency signal (e.g. less than 1 kHz) and preferably less than 512 Hz.
  • a signal of 8 Hz has been found particularly suitable.
  • the existence of a fault may be detected due to the change in measured resistance of the sheath of the cable.
  • a low frequency signal of fixed voltage is applied to the sheath and the current drawn is monitored. Significant current change indicates the presence of a fault.
  • the far end of the line is isolated from ground.
  • a resistive network is set-up.
  • the circuit comprises the resistance of the cable between the fault detection apparatus and the fault, the resistance of the fault, and the resistance from the earth at the fault to the measurement device (which itself is connected to earth).
  • the current taken at the driven end will be higher and the voltage seen at the open end will be lower than obtained from a single fault.
  • This feature can be used to warn an operator of a multiple fault situation in which the impedances and distances calculated may be inaccurate.
  • Such techniques involve measurement of the resistance down the cables through the fault, and back through the ground from two adjacent regeneration stations.
  • Standard network analysis provides equations from which fault resistance and its location can be determined.
  • the resistance measurement at each regeneration station must be coordinated and therefore, in a third aspect, the present invention proposes that one regeneration station be used as a "master" and control signals transmitted to the repeater station at the other end of the section of cable to be tested, with that other repeater station acting as a slave controlled by these signals.
  • the communication channel could be provided by conventional means, such as modems.
  • modems such as modems.
  • the availability of a data link cannot be assumed and interface standards vary. It is another aspect of this invention that the ability to transmit an electrical signal down the length of the cable via the metallic sheath is utilised to create a low speed data link.
  • Fig. 2 shows a detail of the cable
  • Fig. 3 shows a schematic view of the resistance network formed by the arrangement of Fig. 1;
  • Fig. 4 shows the earth spike connection of resistance measurement apparatus
  • Fig. 6 shows a circuit diagram of resistance measurement apparatus for use in the present invention
  • Figs. 8 and 9 show further resistance networks for explaining a development of the present invention.
  • a cable 10 for transmission of e.g. telephone or data signals is connected between a pair of regeneration stations 11,12, assuming the signals are propagating left to right in Fig. 1, the regeneration station 11 amplifies the signal it receives, and applies it to the cable 10.
  • the signal propagates down the cable to regeneration station 12, where it is converted from optical to an electrical signal, amplified, and returned to an optical signal for re-transmission.
  • each regeneration station 11,12 contains resistance measurement apparatus 30,31 connected via an earth spike 11a, 12a respectively to the ground.
  • Each resistance measurement apparatus 30,31 is connected via a switch SW1.SW2 respectively to the armouring 22 of the cable. If a fault occurs at point 13. this earths the armouring 22 at that point.
  • the third influence on the resistance of this network is the resistance effects of the earth stakes 11a, 12a. It has been appreciated by the applicants, as discussed above, that this resistance effect may be reduced to a single equivalent resistance between each earth spike 11a, 12a and true earth. The resistance between true earth at the stake and earth at the fault may then be neglected. These earth stake resistances are therefore shown in Fig. 3 at R g1 and R g2 respectively.
  • Fig. 3 The arrangement of Fig. 3 has neglected however, that the cable will also exhibit capacitance effects along its length and thus the actual circuit is an impedance network. It is not possible to use DC techniques to measure the characteristics of this circuit, because the ground resistance at the earth spikes 11a, 12a prevent satisfactory measurement being obtained. On the other hand, if a high frequency signal is applied to the cable, then the capacitative effects predominate, and the measurement of the resistances becomes impractical. Therefore, the present invention proposes that low frequency AC signals be used. With long cables up to 80 km or more, the capacitance may be as much as 10 ⁇ f, and thus to measure high resistance faults an AC frequency of less than 0.02 Hz would appear to be necessary.
  • a voltage of a known frequency is applied to the armouring 22, and the voltage and current amplitude and phase are measured.
  • This enables the impedance of the load formed by the network to be calculated.
  • By measuring the real and imaginary parts of the voltage and current it becomes possible to separate out the resistance effects, and enables somewhat higher frequencies to be used, although they still have to be low compared with known cable measuring signalling. It has been found that an 8 Hz frequency is suitable, but frequencies of up to 512 Hz are practical.
  • the measurement technique then follows a pattern, for each cable stage between a pair of regeneration stations such as regeneration station 10,12 respectively.
  • the first step is to determine whether or not there is any fault in the cable, and to do this, a simple measurement is taken of the cable resistance. If there is no fault on the line, and with switches SW1,SW2 closed in Fig. 3. then the resistance measured by the resistance measurement apparatus 30 of the regeneration station 11 is:
  • the second step is to locate (strictly "pre-locate") that fault. Then, using a low frequency signal, the network of Fig. 3 is used, but this time with independent measurements from resistance measurement equipment 30 and resistance measurement equipment 31.
  • the ratio of these two gives the percentage distance to the fault 13 along the cable.
  • R f2 R c - R c1 + R f + R g2 Equation 4
  • R f1 - R f2 2R c1 + R g1 - R g2 - R c .
  • R f1 + R f2 R c1 + R c2 + 2R f + R g1 + R g2 Equation 7 Using equation 3 to substitute for R c1 + R c2 , R f can be calculated.
  • the present invention proposes the use of two "dummy" ground spikes 11b, 11e, each of which will have its own ground spike resistance. Referring to Fig. 4, if the ground resistance of the "real" ground spike 11a is R g1 , it is supposed that the ground resistances of the ground spikes 11b, 11e are R b and R c .
  • ground spike resistance R g1 in Fig. 3 can be calculated.
  • the same operation can be used to calculate ground spike resistance R g2 of ground spike 12a, using dummy ground spikes 12b, 12c.
  • resistances R g1 and R g2 may he found and hence the position and value of the fault resistance R f is determined.
  • Fig. 5 modem communication is achieved by encrypting the data 100 for example by frequency shift keying a low frequency carrier (FSK) 101.
  • the modulated signal is applied from one station 11 via an amplifier 102 to the sheath of the cable 10, with the far end receiver unit located in the next regeneration station 12.
  • a short circuit to earth is applied at the far end which provides a complete circuit 103.
  • the modulated carrier may be recovered by sensing via a suitable circuit 104 the current in the sheath of the cable 10.
  • This signal is conditioned by electronic means 105, to allow the data to be demodulated using established circuit techniques 106.
  • a half duplex system allows sequential transmission of data. The hardware required is identified to that described above. Data handling protocols are standard for that used by computer control and communications systems.
  • the resistance measurement apparatus 30,31 comprises three main components, a sine wave generator 51, a voltage and current measurement circuit 52, and a digital system 53.
  • the sine wave generator 51 comprises a clock 54 which generates a frequency at a predetermined value, e.g. 2.097 MHz which is passed to a divider chain 55, and also directly to a part of the voltage and current measurement circuit 52 as will be discussed later.
  • the divider chain 55 divides the frequency from the clock 54 to obtain square waves at two difference frequencies. Each of these square waves is then processed to produce two further square waves at the same frequency and in phase quadrature (i.e. 90°) with each of the original square waves. The two pairs of square waves are then used as phase references by the measurement circuitry.
  • the sine wave signals, which are used in the resistance measurement are derived from the reference square waves by low pass filtering by filters 56.
  • the filtered sine wave is then passed via a buffer amplifier 57 and via a resistor 58 to one end of the "component" 59 to be tested.
  • this "component" 59 is the loop formed by resistors R c1 , R f and R g1 , or by resistors R C2 , R f and R g2 depending on the resistance measurement apparatus 30,31-
  • the technique may also be used for measuring the ground spike resistances of the ground spikes as was described with reference to Fig. 4.
  • a current to voltage converter 60 acts on the current through the component 59.
  • This current to voltage converter 60 may be a standard virtual earth amplifier, the feedback resistance of which is selected in dependence on the known approximate value of the impedance of the component 59 under test.
  • This voltage converter 60 operates so that substantially all the current in the component 59 under test passes through a range resistor 61, and the voltage across this range resistor 61 is therefore directly proportional to the current through the component under test.
  • the measurement circuit 65 which is shown in Fig. 7, comprises an input resistor 70 which receives the input from the filter 64 , and passes i t to a phase sensitive detector 71, and then to a analogue-to-digital converter generally shown at 72.
  • the integrator 73 of the analogue-to- digital converter 72 is supplied with a DC bias from source 74 so that its output voltage has the same polarity.
  • a reference signal is applied to the phase- sensitive detector 71 via logic element 75, which reference signal is one or other of the square wave outputs from the divider chain, at the frequency of measurement.
  • the differential amplifier 62 is switched to be a direct measurement of the voltage across component 59. Again, two voltage measurements are made by the counter 76, one with the in- phase square wave and one with the quadrature square wave.
  • the true voltage and current of the "component" 59 under test may be determined from measurement of the in-phase and quadrature signals, to obtain the current and voltage across the "component" under test, from which its resistance can be determined readily.
  • the cable model of Fig. 3 may be further refined to indicate the bulk resistivity of the ground and the resistivity of the connection method, R g1 and R g2 .
  • the first step is to identify the presence of a fault on the cable; this may be done as previously described. Alternatively with the termination of station 12 open circuit any loop resistance measured from station 11 (using resistance measuring equipment) (118) must be due to a circuit through Rf resistance (114). A preset threshold can be set to indicate a fault.
  • R in1 (s/c) R c1 + R c2 + R BULK1 + R BULK2 + R g1 + R g2
  • Equation 20 indi c ates that the fault resistance can be estimated from three measurements and does not require an estimation of the cable resistance or the ground resistances.
  • the ratio of R c1 and R c2 will be equal to the ratio of distances from the fault to the test sites.
  • Equation 21 Rearranging equations 16 and 17. and dividing one by the other gives: Equation 21
  • Equation 21 shows the ratio of the cable resistance and the bulk ground resistance. The two quantities will vary proportionately with fault distance since they are expressed in a "per unit length" quantity. The result of equation 21 is that the fault distance has been estimated without needing to know the total cable resistance.
  • a further improvement to the technique may be obtained by calculating the open circuit voltage at station 12 when a test is applied at station 11. If the voltage is below that calculated this will be due to one or more additional faults. The operator can be warned that there are multiple faults and that the fault distance estimation will be inaccurate.
  • the present invention proposes that use is made of low frequency signals applied to the conductive armouring of a cable in order to:

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  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Testing Of Short-Circuits, Discontinuities, Leakage, Or Incorrect Line Connections (AREA)
  • Locating Faults (AREA)

Abstract

La présence de défauts dans un câble (10) comprenant un noyau interne (20) et une armature conductrice (22) est détectée en trois étapes. On détecte la présence d'un défaut d'abord en mesurant la résistance de l'armature conductrice (22) et en comparant cette résistance avec la résistance prévue de l'armature (22). Cette opération de détection utilise un signal alternatif d'une fréquence inférieure à 1 kHz. On mesure ensuite la résistance du câble en utilisant un équipement de mesure (30) connecté à la terre par l'intermédiaire de trois crampons de mise à la terre (11A, 11B, 11C). En mesurant d'abord la résistance entre chaque paire de crampons de mise à la terre (11A, 11B, 11C), on peut déterminer la résistance Rg1 d'un crampon de mise à la terre et on peut ensuite ôter cette résistance de la mesure de la résistance du câble. En répétant cette opération en un point éloigné sur le câble (10) au moyen d'un autre équipement de mesure (31) connecté à la terre par l'intermédiaire d'autres crampons de mise à la terre (12A, 12B, 12C), on peut déterminer l'emplacement (13) et la valeur de résistance (Rf) d'un défaut dans le câble (10). Les données peuvent être transmises entre les équipements de mesure (12, 13) à la fréquence inférieure à 1 kHz via l'armature. L'utilisation d'une basse fréquence permet de réduire les effets capacitifs.
PCT/GB1990/000442 1989-03-23 1990-03-23 Detection de defauts dans des cables WO1990011533A2 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
GB898906825A GB8906825D0 (en) 1989-03-23 1989-03-23 Detecting cable faults
GB8906825.8 1989-03-23

Publications (2)

Publication Number Publication Date
WO1990011533A2 true WO1990011533A2 (fr) 1990-10-04
WO1990011533A3 WO1990011533A3 (fr) 1990-11-15

Family

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Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/GB1990/000442 WO1990011533A2 (fr) 1989-03-23 1990-03-23 Detection de defauts dans des cables

Country Status (2)

Country Link
GB (2) GB8906825D0 (fr)
WO (1) WO1990011533A2 (fr)

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
AU634353B2 (en) * 1990-03-09 1993-02-18 Hitachi Limited Power apparatus and method of location of a fault in a power apparatus
US5347212A (en) * 1992-09-09 1994-09-13 Bass Craig D System and method of use for conducting a neutral corrosion survey
US5691644A (en) * 1996-05-10 1997-11-25 Henkels & Mccoy Neutral corrosion condition survey-mitigating induced voltage effects
WO1998058269A1 (fr) * 1997-06-17 1998-12-23 Siemens Aktiengesellschaft Procede et appareil de surveillance d'un cable
EP0920636B1 (fr) * 1996-08-22 2003-12-03 Radiodetection Limited Systeme de depistage de defauts de cables
CN109884450A (zh) * 2019-03-19 2019-06-14 卡斯柯信号有限公司 一种检测应答器电缆状态的装置及方法

Family Cites Families (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US1825754A (en) * 1926-12-03 1931-10-06 Siemens Ag Apparatus for determining the distance to ground connections in electric conductors
US3800216A (en) * 1971-08-11 1974-03-26 Dynatel Corp Cable fault locator apparatus and method with reference voltage comparison
US4063161A (en) * 1975-04-14 1977-12-13 Joslyn Mfg. And Supply Co. Buried cable fault locator with earth potential indicator and pulse generator
SE433405B (sv) * 1982-09-14 1984-05-21 Asea Ab Forfarande och anordning for lokalisering av ett felstelle pa en trefasig kraftledning
SE460804B (sv) * 1988-03-25 1989-11-20 Asea Brown Boveri Foerfarande och anordning foer felbestaemning vid fel paa en kraftledning

Cited By (9)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
AU634353B2 (en) * 1990-03-09 1993-02-18 Hitachi Limited Power apparatus and method of location of a fault in a power apparatus
US5347212A (en) * 1992-09-09 1994-09-13 Bass Craig D System and method of use for conducting a neutral corrosion survey
US5498967A (en) * 1992-09-09 1996-03-12 Henkels & Mccoy, Inc. System and methods of use for conducting a neutral corrosion survey
US5654642A (en) * 1992-09-09 1997-08-05 Henkels & Mccoy System and method of use for conducting a neutral corrosion survey
US5691644A (en) * 1996-05-10 1997-11-25 Henkels & Mccoy Neutral corrosion condition survey-mitigating induced voltage effects
EP0920636B1 (fr) * 1996-08-22 2003-12-03 Radiodetection Limited Systeme de depistage de defauts de cables
WO1998058269A1 (fr) * 1997-06-17 1998-12-23 Siemens Aktiengesellschaft Procede et appareil de surveillance d'un cable
CN109884450A (zh) * 2019-03-19 2019-06-14 卡斯柯信号有限公司 一种检测应答器电缆状态的装置及方法
CN109884450B (zh) * 2019-03-19 2024-04-16 卡斯柯信号有限公司 一种检测应答器电缆状态的装置及方法

Also Published As

Publication number Publication date
GB8906825D0 (en) 1989-05-10
GB9119876D0 (en) 1992-01-02
GB2249841B (en) 1993-05-12
GB2249841A (en) 1992-05-20
WO1990011533A3 (fr) 1990-11-15

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