FAULT METER

Abstract: This invention relates to a method of detecting a fault in an electrical system characterised by the steps of: a) detecting the polarity of the voltage of signal propagated on the system; and b) detecting the polarity of the current of a signal propagated on the system; and c) detecting the magnitude of the current of the signal on the system, wherein a comparatively high current flow indicates the presence of a fault in the electrical system, the method characterised in that the direction of the fault indicated by the high current flow is determined by analysing the polarity of both the voltage and current of this signal.

Description: FAULT METER TECHNICAL FIELD This invention relates to a fault meter. Reference throughout this specification shall be made to the use of the present invention on electric fence systems such as those used for containing animals, or other purposes such as security. It should be appreciated however, that the present invention can be used for other types of systems, and electric fence systems are used by way of example only. BACKGROUND ART Electric fence systems are quite different from other electrical systems. Electric fence systems generally consist of a large single network with literally kilometres of wire connected to a power source which is generally in the form of an electric fence energiser. This network has interconnected multiple branches. In contrast to other electrical systems (such as house wiring), there are few if any individual electrical circuits. Electric fence systems commonly have faults occurring. This is because there is direct access to the wire making up the system. For example, the wire is exposed to all types of adverse conditions, including weather, animals, machinery such as tractors, falling trees, intruders, and so forth. Due to the large size of the electric fence systems and the frequency of faults occurring, it is desirable to have a device or method by which faults can be readily detected. Unfortunately, the peculiarities of electric fence systems mean that traditional methods of fault finding cannot be readily used. One problem is that typically the person trying to find the fault in the electric fence system is an unskilled operator, usually the farmer who owns the electric fence system. Therefore, sophisticated (and usually expensive) electronic devices are unsuitable. Further, with testing systems such as house wiring, it is not thought important to know the direction of a fault as each of the individual circuits making up the house wiring can be tested, thus narrowing the location of the fault down. Testing circuits by directly connecting a multi-meter to a circuit (such as household circuits) is not possible with electric fence systems. This is because the high voltage pulses sent down the system by an energiser can severely damage traditional testing equipment connected directly to the system. Furthermore, traditional testing equipment is unlikely to be capable of measuring high voltage electric fence pulses. There are devices known which are commonly used to detect faults on electric fence systems. These devices generally are not directly coupled to the electric fence system and give an indication (usually by way of an LED) of the current flow. These devices may indicate the magnitude and direction of the current flow. Unfortunately, even if the direction of the current flow is indicated, this will not necessarily show the true direction of the fault as energisers can be installed with reverse polarity. As electric fence systems are very long and have multiple interconnecting branches, the inability to indicate the direction of a fault is understandably a problem. It is an object of the present invention to address the above problems, or at least to provide the public with a useful choice. Further objects and advantages of the present invention will become apparent from the following description which is given by way of example only. DISCLOSURE OF INVENTION According to one aspect of the present invention there is provided a method of detecting a fault in an electrical system characterised by the steps of: a) detecting the polarity of the voltage of a signal propagated on the system; b) detecting the polarity of the current of a signal propagated on the system; c) detecting the magnitude of the current of the signal on the system; wherein a comparatively high current flow indicates the presence of a fault in the electrical system, the method characterised in that the direction of the fault indicated by the high current flow is determined by analysing the polarity of both the voltage and current of the signal. Reference throughout this specification shall be made to the electrical system as being an electric fence system as previously discussed. The signal propagated on the electric fence system may be any signal generated for any purpose on that system. However, it is envisaged that most commonly the signal will be the standard electric energiser pulse which is of a high voltage and occurs approximately every second. Reference to a comparatively high current flow means a higher current flow than is normally expected for standard operation of a fence without any faults. Usually, a fault produces a significant increase in current flow in comparison with the current used in standard operation so that the existence of a fault is relatively easy to detect. However, as discussed previously the direction of the fault can be difficult to determine particularly when electric fence energisers are installed with opposite polarities. The present invention overcomes this problem by analysing the polarity of the voltage and the polarity of the current (of that signal) and using a logic operator to determine the direction of the fault from this information. It is envisaged that there may be a number of ways of connecting the fault meter to the system which is to be analysed. In some embodiments the fault meter can be directly coupled to the system, for instance where an integrated volt meter is utilised. This type of meter will not be damaged as a consequence of the propagation of high voltage pulses along the fence line to which the meter is connected. In preferred embodiments the fault meter is not directly coupled to the system. Instead, the fault meter may be capacitively coupled or may detect the electrical parameters in some other way, perhaps magnetic coupling. In order to determine the polarity of the voltage, the voltage is measured from the electric field of the fence. Other detectors may be used. It should be appreciated that long transmission lines such as electric fence lines are susceptible to picking up noise. Once the noise has been removed by a filter the signal may be amplified by a gain component before the resultant signal passes through a rectifier. The rectifier divides the signal into individual positive and negative components. The voltage polarity of each of the leading edges of component parts is then detected and compared. This information is then passed to a logic operator. Concurrent to the determination of the voltage polarity by the fault meter the magnitude and polarity of the current must also be assessed in order to detect the existence and direction of the fault. In order to assess the polarity and magnitude of the current, the fault meter detects the current of the electrical system using a current detector such as an inductive pick up, for example a current transformer. Other detectors may be used. The signal may then be filtered to eliminate any unwanted electric noise. The signal then passes to autoranging circuitry which allows for the large variations in magnitude of the current found in electric fence systems. For example, close to the electric fence energiser the current may be in the order of 50 Amps. At each node along the electric fence line, the current is effectively split. Thus, some distance along the electric fence line the standard magnitude of current (where there is no fault) could be in the order of only one Amp. The purpose of autoranging circuitry is to ensure that there is accurate scaling on the fault meter so that a meaningful reading can still be made with respect to current level of normal operation at that point on the fence. In some embodiments of the present invention there may be provided a manual reset allowing the operator to indicate a percentage scaling at each node, irrespective of the absolute magnitude of current being measured. This will still allow the presence of a fault to be detected by a comparatively high current flow with respect to the reset scale. Once the signal has been processed by the autoranging circuitry it then passes to a rectifier where the signal is split into two component parts in a similar manner to the voltage as described above. The two component parts of the current signal are then directed into two separate circuits. In one circuit the current polarity is detected and analysed. This information is then passed to a logic operator, which together with the voltage polarity gives a pulse polarity which can be used to determine the direction in which the fault may be found. If there is a negative pulse polarity then the direction of the current flow will be opposite that of the direction of the fault. Whereas if there is a positive pulse polarity the direction of the current flow indicates the direction of the fault. The nature of the Boolean operations undertaken in the logic operator are summarised in Table 1 on page 8A. The resultant information obtained from the logic operator is then passed to a fault direction display to indicate the direction of the fault in the electrical system. Simultaneous to this process in the second circuit the component parts of the current are passed to an accumulator. The magnitude of the resulting signal is then measured. If the measured peak current is within range the signal is passed to the display system which will indicate the amount of current present at that point of the electric fence system. Otherwise, the signal passes back to the autoranging circuitry for readjustment of the scale on the fault meter. If a relatively high current is indicated by the display system, the direction in which the fault lies can be determined from the fault directional display system. It can be seen that the present invention has a number of advantages over the prior art. One problem the present invention overcomes is that an unskilled operator can easily operate the fault meter to detect the presence of a fault within the electrical system. A further advantage is that the fault meter can actually indicate the direction of the fault irrespective of the polarity of the energiser used in the electrical system. BRIEF DESCRIPTION OF DRAWINGS Further aspects of the present invention will become apparent from the following description which is given by way of example only and with reference to the accompanying drawing in which: Figure 1 is a block diagram of the fault meter. BEST MODES FOR CARRYING OUT THE INVENTION Figure 1 illustrates how the fault meter operates to detect the direction and presence of the fault in an electrical system. The fault meter operates by detecting the voltage signal in the electrical system with a voltage detector 1. The signal is then passed to a low pass filter component 2. The signal then passes from the low pass filter component 2 to a gain component 3 where the signal may be amplified, the signal is then passed to a rectifier 4. At that rectifier 4 the detected signal is split into two component parts, the leading edges of which are then detected and the order of the polarities are determined by a voltage polarity order detection component 5. The component parts of the voltage polarity are then compared. The information processed in the voltage polarity order detection component 5 is then passed to a logic operator 6. Concurrent to the above process, the current of the electrical system is also being detected by a current detector 7. The current signal then passes from the current detector to a low pass filter component 8. The signal then passes from the low pass filter component 8 to autoranging circuitry 9 before being passed to a rectifier 10. The rectifier 10 then splits the current signal into two component parts. The two component parts of the signal are then directed into two separate circuits. In one circuit the component parts of the signal pass to a current polarity order detection component 11. Once the polarity of the signal has been determined this information is then passed to the logic operator 6. The logic operator 6 then compares the polarity of the voltage with the polarity of the current. The results of this comparison are then passed to the fault directional display system 12 which indicates the direction of the fault. At the same time as this is occurring the other component parts of the current signal pass from the rectifier 10 to an accumulator 13. From the accumulator 13, the signal is passed to a component which measures the peak current 14. If the peak current is within a useable range this information is passed to the LCD Display System 16. However, if the peak current signal is not within a useable range it passes via a loop circuit 15 back to the autoranging circuitry 9 before again being re-processed by components 10, 1 1 , 6, 12, 13, 14, 16 as described above. Aspects of the present invention have been described by way of example only and it should be appreciated that modifications and additions may be made thereto without departing from the scope thereof as defined in the appended claims.

Claims: CLAIMS: 1 . A method of detecting a fault in an electrical system characterised by the steps of: a) detecting the polarity of the voltage of signal propagated on the system; and b) detecting the polarity of the current of a signal propagated on the system; and c) detecting the magnitude of the current of the signal on the system: wherein a comparatively high current flow indicates the presence of a fault in the electrical system, the method characterised in that the direction of the fault indicated by the high current flow is determined by analysing the polarity of both the voltage and current of this signal. 2. A device capable of detecting faults in an electrical system which includes: a voltage detector of a signal propagated on the system, a current detector of a signal propagated on the system, a voltage polarity detector; a current polarity detector; a current magnitude detector; and a logic operator; wherein a comparatively high current flow indicates that presence of a fault in the electrical system, the device characterised in that the direction of the fault indicated by the high current flow is determined by the polarity of both the voltage and current of the signal, which is analysed by the logic operator. 3. A method or device as claimed in either claim 1 or 2 wherein the electrical system is an electric fence. 4. A method or device as claimed in any one of the preceding claims wherein the signal is a standard electric energiser pulse which is of high voltage and occurs approximately every second. 5. A method or device as claimed in any one of the preceding claims wherein a comparatively high current flow refers to a higher current flow than normally expected for a standard electrical system without any faults. 6. A device as claimed in claim 2 wherein the voltage detector measures voltage from the electric field of the fence. 7. A device as claimed in either claim 2 or claim 6 wherein the device includes a gain component for amplification of the voltage signal. 8. A device as claimed in claim 2 or anyone of claims 6 through 7 wherein the device includes a rectifier capable of dividing the voltage signal into individual positive and negative components. 9. A device as claimed in claim 2 or anyone of claims 6 through 8 wherein the device includes at least one filter. 10. A device as claimed in claim 2 or anyone of claims 6 through 9 wherein the current detector detects the current electrical system via an inductive pick up. 1 1. A device as claimed in claim 2 or anyone of claims 6 through 10 wherein the device includes autoranging circuitry for the current signal. 12. A device as claimed in claim 2 or anyone of claims 6 through 1 1 wherein the device includes a rectifier for splitting the current signal into individual positive and negative components. 13. A device as claimed in claim 2 or anyone of claims 6 through 12 wherein the device includes a component for measuring the peak current. 14. A device as claimed in claim 2 or anyone of claims 6 through 13 wherein the device includes a display system capable of indicating the fault direction. 15. A device as claimed in claim 2 or anyone of claims 6 through 14 wherein the device includes a display system capable of indicating the amount of current detected. 16. A method substantially as herein described with reference to any example and/or drawing thereof. 17. A device substantially as herein described with reference to any example and/or drawing thereof.

Inventors: HO YIT MOON, HO, YIT, MOON
Applicants: GALLAGHER GROUP LTD, HO YIT MOON, GALLAGHER GROUP LIMITED, HO, YIT, MOON
Application year: 1997
Main classification: G01R31
IPC codes: G01R31