WO2010116319A2

WO2010116319A2 - A method and apparatus for monitoring an elongate conductor

Info

Publication number: WO2010116319A2
Application number: PCT/IB2010/051473
Authority: WO
Inventors: Leonardus Gerrardus Philippus Verloop; Leon Pieter Kruyshaar
Original assignee: Individual
Current assignee: Individual
Priority date: 2009-04-06
Filing date: 2010-04-06
Publication date: 2010-10-14
Anticipated expiration: 2011-10-06
Also published as: WO2010116319A3

Abstract

The invention relates to a conductor monitoring apparatus 10 and a method 60 of monitoring an elongate conductor 12. The apparatus 10 may find application in measuring and monitoring the integrity of electrical power cables 12, fluid pipelines or railway tracks. In a preferred embodiment, the apparatus 10 is used to monitor power or telecommunications cables 12. The apparatus 10 includes a Time-Domain Reflectometer (TDR) 11 which is commonly used for measuring the integrity of and locating faults in electrical cables 12 by transmitting an electrical pulse along the cable 12 and measuring pulse reflections. The apparatus 10 further includes a memory module 50 for storing cable operating criteria, a control module 45 for comparing a measured cable integrity against the cable operating criteria, and a communication arrangement 19 for sending an alert message in response to the operating criteria of the cable 12 being violated. The invention aims to simply fault finding, identify illegal taps on power cables 12 and reduce cable theft.

Description

TITLE: A method and apparatus for monitoring an elongate conductor

FIELD OF INVENTION

This invention relates generally to the monitoring of an elongate conductor, such as an electrical cable and specifically to a cable monitoring apparatus and a method of monitoring an elongate conductor.

BACKGROUND OF INVENTION

The Inventors are aware of an existing electronic device known as a Time-Domain Reflectometer (TDR). Currently, a TDR is used for measuring the integrity of and locating faults in electrical cables. The TDR transmits an electrical pulse along the cable. If the cable is properly terminated, little or none of the pulse may be reflected back to the TDR.

However, any impedance discontinuities will cause a portion of the pulse to be reflected back to the TDR from the point of the discontinuity.

The TDR is then operable to determine a time which the reflected pulse took to return, thereby to approximate a location of the discontinuity based on the length of the cable. A particular application of the TDR is for testing the integrity of cable connections.

The Inventors desire an apparatus making use of these principles but which includes cable monitoring functionality.

SUMMARY OF INVENTION

According to one aspect of the invention, there is provided a conductor monitoring apparatus for monitoring the integrity of an elongate conductor, the conductor monitoring apparatus including: a Time-Domain Reflectometer (TDR) operable to transmit an electrical pulse along the conductor thereby to measure a conductor integrity; a memory module having stored thereon conductor operating criteria; a control module operable to compare the measured conductor integrity against the conductor operating criteria thereby to determine whether or not the measured conductor integrity of the conductor violates the operating criteria; and a communication arrangement operable to raise an alert by sending an alert message in response to the measured conductor integrity violating the conductor operating criteria.

In the context of this specification the word "conductor" is defined as a material which is capable of transmitting electricity even though the purpose for which the material is used may not necessarily be for conduction of electricity.

The conductor monitoring apparatus may find application in power cable installations, fluid pipelines or even railway tracks. The conductor monitoring apparatus may therefore be applied to conductors in the form of cables, such as power or telecommunication cables, metal pipes or conduits used to convey fluids such as oil, water or gas, railway tracks or other suitable electrically conductive materials, the integrity of which is to be monitored. Power cables may be powered or unpowered. The conductor monitoring apparatus may be configured specifically for low voltage (< 600 V) installations or for medium voltage installations.

When reference is made to a cable monitoring apparatus in the specification it is to be understood as referring to a conductor monitoring apparatus which is used to monitor the integrity of cables. It is to be appreciated that a security related incident, such as an illegal tap or severing of a cable, may cause a change in impedance of the cable. Thus, the cable monitoring apparatus may be operable to raise the alert in response to such a change in impedance associated with a security related incident. It is to be appreciated that a TDR, in conventional fashion, can measure discontinuities or impedance changes as a function of cable length. Cable integrity measurements may therefore relate to measured impedance characteristics of cables.

Accordingly, the cable operating criteria may be based on one or more previous cable integrity measurements. Thus, if a current cable integrity measurement changes from a previous measurement by, say, 5%, the cable operating criteria may be deemed to be violated. The previous measurement may be a preceding measurement or an initial measurement. The apparatus may be operable to raise the alert in response to a predetermined change in the measured impedance characteristics of the cable when compared to the cable operating criteria.

It may be necessary or desirable to take a reference cable integrity measurement and to define a tolerance (e.g. 5%) by which subsequent measurements may differ, at most, without raising the alert. In other words, the cable monitoring apparatus may be operable to detect a significant change in an impedance characteristic at a particular position in the cable. The cable monitoring apparatus may be operable to detect an impedance change caused by at least one selected from the group composed of: cable damage due to theft or attempted theft; cable damage due to installation of an unauthorised tap; cable deterioration due to moisture ingress, e.g. due to a damaged outer sheath or splice; cable deterioration due to excessive operating temperature, e.g. hot spots or overheating in cable trays; and cable deterioration due to mechanical damage, e.g. due to back hoes or the digging of trenches.

The control module may be configured to raise the alert (e.g. generate and send the alert message) only in response to an impedance change caused by the first two of the above group (i.e. security related incidents) and not by an impedance change caused by the last three of the above group (i.e. general maintenance and deterioration related incidents). The control module may be operable to differentiate between impedance changes caused as a result of deterioration of the cable and impedance changes caused as a result of security related incidents, the control module being configured to generate and send the alert message in response only to impedance changes caused by security related incidents.

The communication arrangement may be in the form of a wireless communication module, such as a Global System for Mobile communications (GSM) modem. The wireless communication module may be operable to communicate across a wireless telecommunications network, such as a cellular telephone network.

The communication arrangement may be operable to send the alert message to a recipient in the form of a control room. The alert message may include an indication of the nature (e.g. an illegal tap) of the violation of the cable operating criteria and an indication of the location of the violation along the cable length.

The cable monitoring apparatus may include a Global Positioning System (GPS) module which is operable to determine a geographic position of the cable monitoring apparatus and to communicate information indicative of the position to the control module.

Upon establishing that the measured cable integrity violates the cable operating criteria and that a security related incident has occurred, and after determining the location of the security related incident as a function of cable length, the control module may be further operable to determine the position of the security related incident using the position information communicated from the GPS module. The communication arrangement may include a radio communication module which is operable to communicate the alert message to a recipient across a wireless communication network utilising a predetermined frequency band.

The memory module may be in the form of at least one Random Access Memory (RAM) module which may be operable to store thereon cable integrity measurements.

The cable operating criteria may allow for changes in impedance at the supply and load ends of a cable, which may result due to a cable feed or legitimate loads being added to the cable. The control module may be configured to ignore these changes in impedance and not raise an alert message in response thereto. Accordingly, the control module may be further operable to filter out allowable changes in impedance to single out security related incidents from amongst legitimate changes in impedance, thereby not sending the alert message in response to a legitimate change in impedance.

According to another aspect of the invention, there is provided a method of monitoring a conductor, the method including: generating conductor operating criteria by taking a reference conductor integrity measurement; storing the conductor operating criteria on a memory module; intermittently measuring the current conductor integrity; comparing the measured conductor integrity against the conductor operating criteria to determine if a violation of the criteria has taken place; and sending an alert message to a remote recipient in response to a violation of the operating criteria.

The conductor may be in the form of an electrical cable which may be powered or unpowered. Generating cable operating criteria may include defining a tolerance by which subsequent measurements may differ, at most, without raising the alert.

It is understood that the impedance of the cable may vary as time passes due to changing environmental conditions. Consequently, the method may include: intermittently updating the cable operating criteria by taking subsequent reference cable integrity measurements; and storing the updated cable operating criteria on the memory module.

If it has been established that a violation of the cable operating criteria has taken place, the method may further include determining the nature and location of the violation as a function of the cable length: more specifically, the method may include determining a geographical position of the violation using information communicated from a GPS module.

The step of measuring the cable integrity may include generating and transmitting an electrical pulse along the cable and receiving reflections of the transmitted pulse caused by impedance discontinuities along the cable.

Comparing the measured cable integrity against the cable operating criteria may include: correlating the transmitted pulse with the received pulse; determining the change in cable impedance over time; and interpreting the change in cable impedance with regard to the cable operating criteria to establish whether or not a security related incident has occurred.

BRIEF DESCRIPTION OF DRAWINGS

The invention will now be further described, by way of example, with reference to the accompanying diagrammatic drawings. In the drawings:

Figure 1 shows a diagrammatic representation of a conductor monitoring apparatus in accordance with the invention; Figure 2 shows a diagrammatic representation of the conductor monitoring apparatus of Figure 1 , implemented in a power cable installation;

Figure 3 shows a hardware block diagram of the conductor monitoring apparatus of Figure 1 ; and

Figure 4 shows a flow diagram of a method of monitoring a conductor, in accordance with the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT

In the Figures, reference numeral 10 refers to a conductor monitoring apparatus in accordance with the invention. In this particular example, the conductor monitored by the apparatus 10 is in the form of a power cable 12. The apparatus 10 is therefore referred to as a cable monitoring apparatus.

Figure 1 shows that the cable monitoring apparatus 10 includes a Time-Domain Reflectometer (TDR) 1 1 which is operable to transmit an electrical pulse along the power cable 12, and to receive reflections of the transmitted pulse caused by impedance discontinuities along the cable 12, thereby to measure the cable integrity. The cable monitoring apparatus 10 includes a memory module 50 capable of storing cable operating criteria. A control module 45 is operable to compare the measured cable integrity against the cable operating criteria in order to determine whether or not the measured cable integrity of the cable 12 violates the operating criteria.

The apparatus 10 also includes a communication arrangement

19 which is operable to communicate with a control room 15 or other remote communication facility. The communication arrangement 19 is in the form of a wireless communication arrangement which is operable to communicate with the control room 15 via a wireless communication network 18, such as a cellular telephone network. The communication arrangement 19, under the direction of the control module 45, is operable to raise an alert by sending an alert message to the control room 15 in response to the measured cable integrity violating the cable operating criteria. The communication arrangement 19 includes a GPS module which is operable to receive Global Positioning System (GPS) position information 53 via a wireless communication network 54.

The cable monitoring apparatus 10 is configured intermittently to measure an impedance characteristic of the cable 12 and to compare it to the cable operating criteria, which may be based upon an initial measurement or a subsequent reference impedance measurement. Accordingly, the control module 45 may be configured to change or update and store the cable operating criteria on the memory module 50. If the measured impedance characteristic differs by more than a predefined amount (e.g. 5%) in comparison with the cable operating criteria, an alert signal is generated and sent by the communication arrangement 19 to the control room 15 through the wireless communication network 18.

With reference to Figure 2, the impedance characteristic of the cable 12 is influenced by, for example, severing of the cable, the connection of authorised and unauthorised taps or loads, the cable feed 23 and mechanical damage to the cable 12, amongst others. Therefore, legitimate loads (e.g. houses) 21 attached to the power cable 12 also cause a change in the impedance characteristic of the cable 12. The apparatus 10 is configured to recognise or identify legitimate changes in impedance and will therefore not raise an alert in response to such changes. As illustrated in Figure 2, the apparatus 10 is attached to the power cable 12 via a line connector 22.

The line connector 22 forms part of a coupling circuit 24, as shown in Figure 3. The coupling circuit 24 is included in the apparatus 10 to ensure that impedance mismatches do not occur between the power cable 12 and circuitry of the TDR 1 1 , which would result in signal losses. The coupling circuit 24 also isolates the apparatus 10 from the high voltage on the power cable 12. The coupling circuit 24 therefore includes a passive impedance matching network 26 which is followed by an isolation transformer 28. Low frequency blocking capacitors 30 are included in series to prevent the transformer from saturating.

The TDR 1 1 operates by generating and transmitting an electrical pulse along the cable 12. Impedance discontinuities on the cable 12 cause a portion of the pulse to be reflected back to the TDR 1 1 . If the cable 12 is properly terminated, little or none of the pulse is reflected back. The apparatus 10 therefore includes a drive circuit 32 which is operable to generate an electrical pulse of sufficient energy and to transmit the pulse along the cable 12. The amplitude of the pulse determines the maximum cable length that can be protected and the steepness of the rise time of the pulse determines the position resolution of the apparatus 10. The position resolution is defined as the minimum distance two discontinuities can be apart in order for the apparatus 10 to still be able to distinguish between the two discontinuities. In order to adjust the amplitude of the pulses applied to the cable 12, the supply voltage 35 of the drive circuit 32 must be variable. This is done through software and requires a Digital-to-Analogue Converter (DAC) 33 and a buffer amplifier 34. The drive circuit 32 works through a push-pull driver arrangement which incorporates internal impedance adjustment 37 for varying applications of the apparatus 10.

Once the reflected pulse has passed through the coupling circuit 24, it passes through a Programmable Gain Amplifier (PGA) 39 which adjusts the amplitude of the reflected pulse to ensure that it is within the dynamic range of associated circuitry. The gain of the PGA 39 may also be adjustable through software to compensate for changing conditions on the cable 12. The pulse then passes through a Time Delay Compensation stage 40 which is a non-linear amplification stage to compensate for the signal attenuation of the reflected pulse. If r represents the distance the discontinuity is from the apparatus 10 then the reflected pulse attenuates by a factor of V_A . The analogue reflected pulse is required to be converted to digital form in order for signal processing to be performed. For this reason, the pulse is passed through an Anti-Aliasing Filter (AAF) and buffer amplifier 42 before it is converted to digital form by an Analogue-to-Digital Converter (ADC) 43. The AAF 42 is a Low Pass Filter (LPF) that eliminates the high frequency noise from the input to the ADC 43 to prevent aliasing when the measured signal is sampled. A Low Jitter Clock 44 controls the timing of the ADC 43. Once in digital form, the signal is passed to the control module 45 for further signal processing. The control module 45 is not only responsible for the processing of the measured signal, but also for the generation of the code to produce the pulse that is transmitted along the cable 12. The control module 45 includes a Field Programmable Gate Array (FPGA) Processor 46 which performs very high speed signal processing and a Floating Point Digital Signal Processor (DSP) 48 which performs system control and signals alerts to the control room 15.

The apparatus 10 also includes a memory module 50 which includes storage capacity in the form of Synchronous Dynamic Random Access Memory (SDRAM) modules 51 which can be used to store the previous measured impedances characteristics of the cable 12. The control module 45 is operable to compare the measured impedance characteristics against the cable operating criteria and to generate an alert signal if the change in impedance is greater than a predefined tolerance.

Included in the communication arrangement 19 is a Global

System for Mobile communications (GSM) modem 52 and a Global Positioning System (GPS) module 52. The GSM modem 52 facilitates the communication between the apparatus 10 and the control room 15. The GPS module 52 is operable to receive GPS position information 53 through the wireless communication network 54. The position information 53, together with an indication of the position on the cable 12, is used to determine the geographic location of discontinuities on cables 12, which aids in fault finding. The control module 45 includes a position location system 55 which is operable to determine the geographic location of irregularities or discontinuities. The communication arrangement 19 also includes a radio communication module 57 which is in the form of a licensed radio unit supplied by a security and response company. If an alert signal is generated, then the licensed radio unit can be used to notify the security company.

In Figure 4, reference numeral 60 refers generally to a method of monitoring a cable in accordance with the invention. The method 60 includes generating, at block 62, cable operating criteria by taking a reference cable integrity measurement. Generating the cable operating criteria further includes defining a tolerance by which subsequent integrity measurements may vary without the alert being raised. The cable operating criteria are then stored, at block 64, on the memory module 50. Due to changing conditions, the impedance characteristic of the cable 12 may vary, and therefore, the method 60 includes the option of updating, at block 66, the cable operating criteria. If it is desired to update the operating criteria, a reference impedance measurement is taken, at block 68, and the criteria is updated, at block 69, before the newly updated criteria is stored 64 again on the memory module 50.

The method 60 further includes intermittently measuring, at block 70, the current cable integrity. This measured cable integrity is then compared, at block 72, against the operating criteria, to determine whether or not the current measurement violates the criteria. Comparing involves averaging of the received pulses in order to improve the Signal to Noise Ratio (SNR) and matched filtering or correlating the received pulse with the transmitted pulse. The resultant signal is passed through a Low-Pass Filter (LPF) in order to suppress high frequency noise in the signal. The change in impedance over time is determined by subtracting the (k-1)th sample from the kth sample, and this is compared with the operating criteria to determine, at block 74, whether or not a violation has taken place. If a violation of the cable operating criteria has taken place, then the nature and the location of the violation is determined, at block 76, using position information 53 communicated from the GPS module 52. Finally the alert message is sent, at block 78, to the control room 15 so that a human operator can act accordingly. The alert message contains information indicative of the nature and the location of the violation.

It is understood that the apparatus 10 is able to operate from a 12 Volt Direct Current (DC) battery power supply and that it is also able to operate from mains power. Therefore, the apparatus 10 can be used to monitor cables which are not powered as well as powered cables. It is further understood that the power supply of the apparatus 10 includes surge protection and over current protection circuitry. The apparatus 10 is also designed to eliminate external Electromagnetic Interference (EMI) such as

Electrostatic Discharge (ESD), voltage dips, harmonics and other radiated electromagnetic fields.

The Inventors believe that the cable monitoring apparatus 10 as described above enhances the security of cables against security related incidents, such as an illegal tap or cable theft and provides an effective means of continually monitoring such cables, including power cables. The Inventors further believe that the cable monitoring apparatus 10 will not only be effective in raising an alert if a security related incident is encountered, but might also be able to detect the deterioration of cables. The application of the cable monitoring apparatus can therefore save costs by reducing cable theft and illegal taps, and save time by simplifying fault finding, by isolating a fault to a particular area on a length of cable.

Claims

CLAIMS:

1 . A conductor monitoring apparatus for monitoring the integrity of an elongate conductor, the apparatus including: a Time-Domain Reflectometer (TDR) operable to transmit an electrical pulse along the conductor thereby to measure a conductor integrity; a memory module having stored thereon conductor operating criteria; a control module operable to compare the measured conductor integrity against the conductor operating criteria thereby to determine whether or not the measured conductor integrity of the conductor violates the operating criteria; and a communication arrangement operable to raise an alert by sending an alert message in response to the measured conductor integrity violating the conductor operating criteria.

2. A conductor monitoring apparatus as claimed in claim 1 , wherein the conductor is in the form of a powered electrical cable and the apparatus is configured to monitor the cable in low to medium voltage installations.

3. A conductor monitoring apparatus as claimed in claim 1 , wherein the conductor is in the form of an unpowered electrical cable.

4. A conductor monitoring apparatus as claimed in claim 2 or claim 3, wherein the cable operating criteria are based upon one or more previous measured impedance characteristics of the cable and the apparatus is operable to raise the alert in response to a predetermined change in the measured impedance characteristics of the cable when compared to the cable operating criteria.

5. A conductor monitoring apparatus as claimed in claim 4, wherein the monitoring apparatus is operable to detect a change in impedance of a cable caused by at least one selected from the group composed of: cable damage due to theft or attempted theft; cable damage due to installation of an unauthorised tap; cable deterioration due to moisture ingress as a result of a damaged outer sheath of the cable; cable deterioration due to excessive operating temperatures; and cable deterioration due to mechanical damage.

6. A conductor monitoring apparatus as claimed in claim 5, wherein the control module is operable to differentiate between impedance changes caused as a result of deterioration of the cable and impedance changes caused as a result of security related incidents, the control module being configured to generate and send the alert message in response only to impedance changes caused by security related incidents.

7. A conductor monitoring apparatus as claimed in any of the preceding claims, wherein the communication arrangement is in the form of a wireless communication module, the wireless communication module being operable to communicate across a wireless telecommunications network.

8. A conductor monitoring apparatus as claimed in claim 7, wherein the wireless communication module is in the form of a Global System for Mobile communications (GSM) modem.

9. A conductor monitoring apparatus as claimed in claim 7, wherein the communication module includes a radio communication module which is operable to communicate the alert message to a recipient across the wireless communication network utilising a predetermined frequency band.

10. A conductor monitoring apparatus as claimed in any of the preceding claims, wherein the alert message includes an indication of the nature of the violation of the conductor operating criteria and an indication of the location of the violation along the conductor length.

1 1. A conductor monitoring apparatus as claimed in any of the preceding claims, including a Global Positioning System (GPS) module which is operable to determine a geographic position of the apparatus and to communicate information indicative of the said position to the control module.

12. A conductor monitoring apparatus as claimed in any of claims 4 to 1 1 inclusive, wherein the control module is operable to filter out allowable changes in impedance to single out security related incidents from amongst legitimate changes in impedance, thereby sending no alert message in response to a legitimate change in impedance.

13. A method of monitoring a conductor, the method including: generating conductor operating criteria by taking a reference conductor integrity measurement; storing the conductor operating criteria on a memory module; intermittently measuring the current conductor integrity; comparing the measured conductor integrity against the conductor operating criteria to determine if a violation of the criteria has taken place; and sending an alert message to a remote recipient in response to a violation of the operating criteria.

14. A method as claimed in claim 13, wherein the conductor is in the form of an electrical cable.

15. A method as claimed in claim 14, including: intermittently updating the cable operating criteria by taking subsequent reference cable integrity measurements; and storing the updated cable operating criteria on the memory module.

16. A method as claimed in claim 14 or claim 15, which upon establishing that a violation of the cable operating criteria has taken place, includes: determining the nature and location of the violation as a function of the cable length; and determining a geographical position of the violation using information communicated from a GPS module.

17. A method as claimed in any of claims 14 to 16 inclusive, wherein measuring the cable integrity includes generating and transmitting an electrical pulse along the cable and receiving reflections of the transmitted pulse caused by impedance discontinuities along the cable.

18. A method as claimed in any of claims 14 to 17 inclusive, wherein comparing the measured cable integrity against the cable operating criteria includes: correlating the transmitted pulse with the received pulse; determining the change in impedance over time; and interpreting the change in impedance with regard to the cable operating criteria to establish whether or not a security related incident has occurred.