WO1996006362A1 - Localisation d'une defectuosite dans un cable electrique - Google Patents

Localisation d'une defectuosite dans un cable electrique Download PDF

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Publication number
WO1996006362A1
WO1996006362A1 PCT/GB1995/001911 GB9501911W WO9606362A1 WO 1996006362 A1 WO1996006362 A1 WO 1996006362A1 GB 9501911 W GB9501911 W GB 9501911W WO 9606362 A1 WO9606362 A1 WO 9606362A1
Authority
WO
WIPO (PCT)
Prior art keywords
fault
cable
signal
distance
sampling period
Prior art date
Application number
PCT/GB1995/001911
Other languages
English (en)
Inventor
Andrew Biggerstaff Lewis
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 WO1996006362A1 publication Critical patent/WO1996006362A1/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
    • G01R31/08—Locating faults in cables, transmission lines, or networks
    • G01R31/081—Locating faults in cables, transmission lines, or networks according to type of conductors
    • G01R31/083—Locating faults in cables, transmission lines, or networks according to type of conductors in cables, e.g. underground
    • 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
    • G01R31/08—Locating faults in cables, transmission lines, or networks
    • G01R31/088—Aspects of digital computing

Definitions

  • the present invention relates to the location of faults in cables, such as low voltage power cables.
  • One known method of determining the location of the fault relative to a fixed point in the cable is to use a pulse-echo or Time Domain Reflectometry technique. This technique is disclosed in e.g. the book "Underground Cable Fault Location" by B Clegg pp 42-71. In such a technique, a known signal pulse is applied to the faulty cable, and that pulse is reflected at the fault. By determining the time between the transmission of the pulse, and the reception of its reflection, the distance to the fault may be estimated. When the cables are to carry multi-phase currents, it is necessary to prevent the pulse passing onto parallel cables, which could provide multiple reflections.
  • GB-A-1539118 provided a plurality of detectors along the cable. For a buried cable, this is inconvenient since all the detectors have to be buried with the cable and be arranged to transmit their voltage measurement data to a control processing site. This increases the complexity of the detectors. Moreover, for the voltage gradient technique to be used, there need to be detectors on each side of the fault, and the accuracy of the measurement depends on the spacing of the detectors, hence a large number of detectors must be used.
  • the present invention is based on the realization that the waveform of the signal on the cable at the time of the fault contains sufficient information to enable the distance between a single measurement point and the fault to be determined. Analysis of that waveform by autocorrelation techniques thus enables a single measurement point, and hence a single detector, to be used.
  • the present invention seeks to make use of the normal current that is present on the cable, in order to detect the position of the fault.
  • the current waveform will have components which enable the fault to be located.
  • the signal on the cable is continuously sampled, for successive sampling periods. Then, when a break in supply due to a fault is detected in any sampling period, the sample of a previous (usually the immediately previous ) period is investigated to determine the waveform components present during that previous period, which then enables the fault to be located.
  • This investigation of the sample of a preceding period is triggered by e.g. disconnection of supply or tripping of fuses detected by voltage monitoring, when the signal on the cable has dropped to a predetermined level because of the existence of the fault. Normally, when there is a fault, the signal of the cable will decay with time-repeating components, and by looking at a preceding sampling period, those components can be investigated, for the time interval therebetween enabling the distance from the fault to be determined.
  • the signal needs to be sampled at a rate which is high enough accurately to represent the highest frequency of interest, which will determine the range resolution. If the sampling period is too short, insufficient information will be obtained. Any such insufficiencies generally limit the resolution of distance that can be obtained. Thus, to achieve a resolution of x (i.e. to determine the location fault to a particular length x of the cable), it is necessary to sample at a rate greater than K.c/x where K is the velocity of propagation in the cable. The signal should be sampled long enough to record a number (e.g. 3) round trips from the most distant possible fault to the measuring site. The maximum length of the sampling period is determined by the size of the buffer in which the sample or samples are to be stored.
  • the present invention can be used to derive the distance between a single measurement point and the fault, thereby permitting a single detection to be used.
  • the accuracy of the measurement of the fault position then decreases with the distance from the detector to the fault.
  • it is possible to use two or more detectors with known separation( s ) to measure the distance between the fault and each detector, and then to compare the distance measurements thus obtained, using the known detector separation(s) to reduce the error in the determination of the location of the fault.
  • a plurality of detectors may be mounted in a portable unit which is brought into proximity of the cable when a measurement is to be made.
  • each detector is used to measure the distance between that detector and the fault, it is not necessary to provide detectors all along the cable as in GB-A-1539118. Moreover, since the determination of the position of the fault does not use voltage gradient technique, it is not necessary for there to be detectors on both sides of the fault.
  • the current on the signal is investigated, e.g. by use of a suitable transformer coupled to the cable.
  • a suitable transformer coupled to the cable.
  • Such a transformer may be of the split-core type, since this can be applied around the cable at a convenient location so that the distance to the fault can be determined whilst the cable remains operational. This is particularly useful where the fault dries-out the insulation, since the first occurrence of the fault may then trigger the placing of the transformer around the cable, to detect a subsequent insulation failure later.
  • Fig. 1 shows a cable fault location arrangement, being a first embodiment of the present invention
  • Fig. 2 shows a cable fault location arrangement being a second embodiment of the present invention
  • Figs. 3A and 3B are auto-correlation functions used in the present invention.
  • Fig. 4 is a cable fault location arrangement being a third embodiment of the present invention.
  • Fig. 5 is a block diagram showing an investigation device for use in the embodiments of Fig. 1, Fig. 2 or Fig. 3;
  • Fig. 6 is a schematic view of the waveform that will be sampled using the present invention.
  • a cable 10 is connected to a transformer 11, which transformer applies a signal to a cable 10.
  • a split-core current transformer 12 is mounted around the cable, and connected to a current investigation device 13.
  • a fault 14 occurs at a point P on the cable, a high current flows which can be detected by a suitable detector to break the connection between the transformer 11 and the cable 10. This can be achieved by disconnection or tripping of a fuse or circuit breaker.
  • the behaviour of the signal on the cable 10 is investigated by the investigation device 13 for the period immediately prior to the occurrence of the high current.
  • the investigation device 13 continuously samples the current on the cable 10, and when the high current occurs in any sampling period, the immediately preceding sampling period is investigated.
  • Such investigation involves analysis of the signal on the cable 10, using autocorrelation techniques well known in investigation of signals.
  • autocorrelation techniques are discussed in e.g. "Digital Signal Process - A Practical Approach" by I Leachor and Jervis, published by Addison-Wesley pp6-10, the book “Introduction to Digital Signal Processing” by Proalas and Manolalis published by Maxwell-Macmillian pplll- 115.
  • the signals will have time-repeating elements which permit the distance between the split-core transformer 12 and the fault point P to be determined, making use of the signals and the reflection of the signals from the fault.
  • the investigation device 13 may employ a circular buffer memory which stores data corresponding to the signal for the immediately preceding time period, at the same time that it is receiving the data corresponding to the data corresponding to the signal for the current time period.
  • a circular buffer memory which stores data corresponding to the signal for the immediately preceding time period, at the same time that it is receiving the data corresponding to the data corresponding to the signal for the current time period.
  • Fig. 1 The embodiment of Fig. 1 is satisfactory where the is a single cable 10. However, as shown in Fig. 2, the cable 10 may branch into separate branches 20, 21 and 22. If a fault 14 occurs at a point FI, measurement using a split-core current transformer 12 and device 13, as in the embodiment of Fig. 1, means that the distance to the fault can be determined, but the branch 20, 21, 22 in which the fault is present cannot be determined. Thus, if the arrangement of Fig. 1 is used, the system can detect that there is a fault at points FI, F2, F3, being points on the branches 20, 21, 22 which are equidistant from the split-core current transformer 12, but cannot determine which corresponds to the fault.
  • voltage monitors 23, 24 and 25 are connected to the respective branches 20, 21 and 22 such as by way of a live power socket.
  • Each voltage monitor 23, 24, 25 continuously and periodically samples the voltage waveform on the respective branch 20, 21, 22 of the cable and stores signals corresponding to that voltage waveform for preceding sampling periods.
  • the voltage waveform will be sinusoidal.
  • a fault in the cable will produce a waveform dependent on the location of the fault. Assuming that the fault is at point FI on branch 21, the voltage waveform detected by the voltage monitor 24 will decay virtually to zero. The same fault will cause changes in the signals to the voltage monitors 23, 25 but these will have a quasi- sinusoidal decay pattern which will depend on the fault distance.
  • Figs. 3A and 3B show the auto-correlation function used when the fault is relatively close, whereas Fig. 3B shows auto ⁇ correlation function when the fault is relatively distant.
  • the accuracy of location of the point P at where the fault 14 occurs will depend on the distance between that point P and the split-core current transformer 12. If this distance along the cable 10 is too large, the location of the fault 14 may be insufficiently accurate.
  • the embodiment of Fig. 4 may be used.
  • a portable receiver 30 which has a pair of aerials 31,32 which detect magnetic fields.
  • the aerials 31, 32 are arranged so that they can be parallel to the cable 10, since in that state they will not detect any magnetic fields due to the signal on the cable 10 itself.
  • the direction of the fault current causes magnetic fields to be generated which will be detected by the aerials 31, 32.
  • the outputs of the aerials 31, 32 are monitored continuously, and periodically, and samples stored in a buffer in a similar way to the other embodiments, then a section of high current caused by the fault will enable preceding sampling periods for the receiver 30 to be investigated.
  • the investigation device 13 may generate a transmission signal 33 on detection of that high current, which triggers the investigation of signals stored by the receiver 30.
  • Fig. 5 shows the structure of the investigation device 13 used in the embodiment of Fig. 1, Fig. 2 or Fig. 4.
  • the signal from the transformer 12 passes via an amplifier 40, a high-pass filter 41 and a further amplifier 42 to an analogue-to-digital converter 43.
  • the digital signal thus generated is passed to a buffer in the form of a RAM 44 in which the digital data is stored.
  • the storing of the data in the RAM 44 is controlled via a CPU 45 and an address generator 46.
  • the CPU 45 and the address generator 46 ensure that, at all times, there is data corresponding to at least one sampling period in the RAM 44.
  • Data thus arriving at the RAM 44 is immediately stored therein at addresses determined by the address generator 46, and data which was collected in an earlier sampling period, and is now no longer necessary, is deleted from the RAM 44.
  • the CPU 45 determines, at any time, which data needs to be retained in the RAM 44 and which can be deleted.
  • Fig. 6 shows a typical sample at the time of a fault. Initially, prior to the occurrence of the fault, the signal has a sinusoidal characteristic 50. When the fault occurs, at time T, however, there is a sudden change in the current and an oscillation occurs which then determines the distance of the fault.
  • Fig. 6 represents a sample backwards in time from point S at which the tripping of a fuse or circuit- break occurs, and the CPU 45 is triggered to release the sample from the RAM 44.
  • the length of the sampling period, backwards from the point S thus needs to be sufficiently long to ensure that a suitable sample is obtained.
  • the sample should be long enough to record a suitable number (e.g.

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  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Engineering & Computer Science (AREA)
  • Mathematical Physics (AREA)
  • Theoretical Computer Science (AREA)
  • Locating Faults (AREA)

Abstract

Selon l'invention, un système d'investigation (13) connecté à un transformateur à pipe (12) permet de localiser une défectuosité dans un câble (10) acheminant un signal émis par un transformateur (110) en maintenant ce signal. Le système d'investigation (13) contrôle en permanence l'intensité du courant par périodes successives d'échantillonnage et examine les données relatives à la période d'échantillonnage immédiatement antérieure dès qu'un courant à haute intensité est détecté en raison d'une défectuosité. Il est possible de déterminer la distance séparant le transformateur à pipe du point (P) défaillant par la technique de l'autocorrection. Le système d'investigation peut faire appel à une mémoire tampon qui stocke les données relatives à la période d'échantillonnage immédiatement antérieure en même temps qu'elle reçoit les données relatives à la période d'échantillonnage en cours. S'agissant de câbles dérivés, il peut s'avérer nécessaire de contrôler la tension de chaque dérivation, afin d'être en mesure d'identifier ladérivation défaillante.
PCT/GB1995/001911 1994-08-19 1995-08-14 Localisation d'une defectuosite dans un cable electrique WO1996006362A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
GB9416859A GB9416859D0 (en) 1994-08-19 1994-08-19 Cable fault location
GB9416859.8 1994-08-19

Publications (1)

Publication Number Publication Date
WO1996006362A1 true WO1996006362A1 (fr) 1996-02-29

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Application Number Title Priority Date Filing Date
PCT/GB1995/001911 WO1996006362A1 (fr) 1994-08-19 1995-08-14 Localisation d'une defectuosite dans un cable electrique

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GB (1) GB9416859D0 (fr)
WO (1) WO1996006362A1 (fr)

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN113484688A (zh) * 2021-07-22 2021-10-08 云南电网有限责任公司昆明供电局 基于馈线电流骤减度的配电网故障研判方法及系统

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE2712570A1 (de) * 1976-03-22 1977-09-29 Electricity Council Verfahren und vorrichtung zur aufspuerung von fehlern in elektrischen niederspannungsleitungskabeln
EP0078183A2 (fr) * 1981-10-27 1983-05-04 THE GENERAL ELECTRIC COMPANY, p.l.c. Localisation de défauts dans les lignes de transmission d'énergie
DE3636367A1 (de) * 1986-10-25 1988-04-28 Licentia Gmbh Verfahren und vorrichtung zur feststellung der entfernung und der richtung von erdschluessen in isolierten und kompensierten starkstromnetzen
DE3812433A1 (de) * 1988-04-14 1989-10-26 Siemens Ag Verfahren zur bestimmung des fehlerortes auf einer elektrischen leitung

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE2712570A1 (de) * 1976-03-22 1977-09-29 Electricity Council Verfahren und vorrichtung zur aufspuerung von fehlern in elektrischen niederspannungsleitungskabeln
EP0078183A2 (fr) * 1981-10-27 1983-05-04 THE GENERAL ELECTRIC COMPANY, p.l.c. Localisation de défauts dans les lignes de transmission d'énergie
DE3636367A1 (de) * 1986-10-25 1988-04-28 Licentia Gmbh Verfahren und vorrichtung zur feststellung der entfernung und der richtung von erdschluessen in isolierten und kompensierten starkstromnetzen
DE3812433A1 (de) * 1988-04-14 1989-10-26 Siemens Ag Verfahren zur bestimmung des fehlerortes auf einer elektrischen leitung

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN113484688A (zh) * 2021-07-22 2021-10-08 云南电网有限责任公司昆明供电局 基于馈线电流骤减度的配电网故障研判方法及系统

Also Published As

Publication number Publication date
GB9416859D0 (en) 1994-10-12

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