Method for accurately locating cable faults of buried cables

Abstract

The present invention relates to a method for precisely locating a cable fault in an underground cable for transmitting electrical energy, wherein a mobile precise positioning device, at a first and a second, different current position of the precise positioning device, determines first and second position measurements for the respective current position of the precise positioning device and first and second distance measurements for the respective distances of the precise fault location from the respective current position of the mobile precise positioning device by means of a GPS receiver of the precise positioning device, thereby determining at least one possible fault location. At least one target location corresponding to at least one of the possible fault locations is displayed on a display device of the precise positioning device in a map of the surroundings of the approximate location of the cable fault, stored in the precise positioning device, or in an image captured by a camera of the mobile precise positioning device.

Description

Technical Field

[0001] The present invention relates to a method for accurately locating cable faults in buried cables for transmitting electrical energy, wherein, in order to determine the exact fault position of the cable fault, based on the approximate position of the cable fault previously determined by pre-positioning, the corresponding distance between the defective position of the cable and the corresponding current position of the mobile precise positioning device is determined with the help of a mobile precise positioning device. Background Art

[0002] Buried cables used for transmitting electrical energy may develop faults that require cable repairs in the area of the defect. These may involve low-voltage, medium-voltage, or high-voltage cables. To perform the repair, the cable fault must first be located. A location vertically above the cable fault (the "fault location") is identified, and excavation is performed at this location to reveal the lower portion of the cable where the cable fault is located. Methods for this are known.

[0003] Known methods for locating cable faults first perform a pre-positioning (rough location). An example of this is the secondary multiple pulse method, a high-voltage measurement method suitable for high-resistance cable faults. To locate the cable fault, the first reflection of a voltage pulse at the cable end and the second reflection caused by the breakdown at the defect location are detected. Other known methods for locating the fault include the decay method and ICM.

[0004] As a result of this pre-positioning, the cable length between the location where the pre-positioning signal was fed and the location of the cable defect is determined. If the cable route (the cable's path through the ground) is known, the location of the cable fault can therefore be determined. Geographical data for the cable route is available, or the path of the buried cable must be determined. This path (cable path) is determined, for example, by feeding audio into the underground cable and using a detection coil guided above ground along the cable route.

[0005] However, known methods for pre-locating cable faults only provide an approximate location of the cable fault. This is due, in particular, to the fact that when laying the cable along the cable route, more or less significant deviations from the shortest path occur. Consequently, the laying depth may vary, cable loops may occur, and so on. Overall, this results in an inaccuracy in pre-locating cable faults, which typically ranges from 1% to 10% of the cable length between the point where the measurement signal is fed in and the cable fault. Consequently, depending on the length of the path, the deviation between the exact fault location of the cable fault and the approximate location determined by pre-locating the cable fault may range from a few meters to several hundred meters.

[0006] It is also known to display the determined approximate location of a cable fault on a map. Pre-positioning is performed using a pre-positioning device, typically located in a survey vehicle within the range of the cable station where the cable runs originate. The cable runs are known as "GIS data" and can be stored in the pre-positioning device. After the user inputs the starting point of the cable to be pre-positioned and the distance to the cable fault is determined, the approximate location of the cable fault can be displayed on a map displayed on the display unit of the pre-positioning device. The pre-positioning device can also include a GPS receiver, so that the position of the survey vehicle can also be displayed on the map. The fault location personnel can then use satellite navigation to navigate to the approximate location of the cable fault.

[0007] In order to determine the exact fault location of the cable fault based on the pre-positioning (rough positioning) performed previously, acoustic precision positioning methods are known so that excavation work can be carried out at this location further along the path. In this case, a surge voltage pulse is fed into the cable with the help of a surge voltage generator. The high-energy pulse causes a voltage pulse that propagates in the cable, which causes a breakdown at the defect location. Here, a signal is generated in the vicinity of the cable fault that can be detected by a seismic detector. The seismic detector can now be used to find the location of the highest amplitude of the breakdown noise in order to determine the fault location of the cable fault. In each measurement, the seismic detector is placed on the ground and waits for the next surge voltage pulse and the acoustic signal triggered thereby. However, this method of fault finding is very time-consuming.

[0008] The improvement to this method is to determine the distance between the cable defect location and the current position of a mobile, precise locating device. To this end, the mobile, precise locating device, in addition to a geophone for detecting acoustic signals, also includes an electromagnetic sensor. This electromagnetic sensor detects surge voltage pulses transmitted through the cable and the resulting electromagnetic field. A time difference is detected between the detected electromagnetic signal and the detected acoustic signal. This time difference corresponds to the time required for the acoustic wave caused by the breakdown to travel from the defect location to the mobile, precise locating device (where the propagation time of the surge voltage pulse is negligible). Therefore, the distance between the defect location and the current position of the mobile, precise locating device can be determined based on this determined time difference. This distance is displayed on the mobile, precise locating device. Therefore, personnel locating cable faults can determine whether the distance to the faulty device has decreased by repeating measurements. If this distance reaches a minimum, the personnel are directly above the cable defect location, i.e., at the precise fault location. This significantly simplifies the search for the precise fault location.

[0009] An acoustic pinpointing method for analyzing the time difference between an acoustic signal and a surge voltage pulse to determine the distance to a cable fault is known, for example, from EP 2 405 279 A2. This document discloses a method in which acoustic pinpointing can be performed even under very noisy ambient conditions.

[0010] In addition to devices for fault location that are used only after a cable fault has occurred, so-called "online monitoring" is also known, which permanently monitors the cable during operation. For this purpose, fixedly installed, static monitoring devices are used.

[0011] CN 105676074A discloses a device for online monitoring of high-voltage power lines installed as overhead lines. Measuring units are installed on high-voltage power poles at intervals of 5 to 50 km. These units detect traveling waves that occur during sparkover. GPS is used for time synchronization, and the time differences between the arrival of the traveling waves are analyzed at a base station to approximate the location of the defect. Summary of the Invention

[0012] The object of the present invention is to further simplify the finding of the exact position of a cable fault in a method of the type mentioned at the outset. This is achieved according to the invention by a method having the features of claim 1 .

[0013] In the method of the present invention, the current position of the precise positioning device is detected using its GPS receiver, thereby obtaining a "position measurement value." These position measurements are detected at a first and a second, different current position of the precise positioning device. At the first and second current positions of the precise positioning device, the distances of the precise fault location from the respective current positions of the mobile precise positioning device are also detected, thereby obtaining a "distance measurement value." Using the first and second position measurements and the first and second distance measurements, at least one previously unknown possible fault location is determined. This determination is performed in such a way that for a possible fault location to exist, its distance from the first position measurement value must correspond to the first distance measurement value, and its distance from the second position measurement value must correspond to the second distance measurement value. Typically, measurements at two different current positions of the precise positioning device result in two possible fault locations, one of which corresponds to the actual precise fault location. However, if the two current positions of the mobile precise positioning device (at which the position and distance measurements were determined) lie on a straight line, and the precise fault location also lies on this line (with reference to a plan view), only one possible fault location is obtained, which then already corresponds to the precise fault location.

[0014] A map of the environment of the approximate location of the cable fault, stored in the precise positioning device, and an image captured by a camera of the mobile precise positioning device, are displayed on the display device of the precise positioning device. At least one target location is shown on the map or in the image, corresponding to at least one of the possible fault locations thus determined. Thus, the user is presented with the at least one displayed target location where the actual fault location is likely to be located.

[0015] If two possible fault locations result from the determination of position and distance measurements at the first and second current positions of the precise positioning device, the mobile precise positioning device can advantageously determine a third position measurement and a third distance measurement for the distance of the precise fault location from the third current position of the mobile precise positioning device at a third current position of the precise positioning device that is different from the first and second current positions and that is not located on a common straight line with the first and second current positions of the precise positioning device (with reference to the plan view). The third position measurement and the third distance measurement can be used to determine which of the two previously determined possible fault locations corresponds to the precise fault location by determining at which of the two possible fault locations the distance from the third current position of the precise positioning device corresponds to the third distance measurement. The possible fault location that corresponds to the precise fault location can then be displayed as a target location on a display of the precise positioning device, specifically in a map displayed on the display or in an image captured by a camera displayed on the display.

[0016] Thus, the method according to the present invention directly displays at least one target location, preferably exactly one target location, for the possible precise fault location of a cable fault on a map or in an image, allowing the user to move directly to the target location. This simplifies and accelerates finding the precise fault location of the cable fault so that excavation work can be carried out there to expose the cable and carry out repairs.

[0017] Thus, the determination of at least one possible fault location (which is then displayed as a target location on the display of the pinpointing device) can be performed without considering the cable's reference plan course. Therefore, the cable course itself does not necessarily need to be known or stored in the pinpointing device. If the cable course is known and stored in the pinpointing device, for example, by transmission from a GIS database, it can also be displayed on a map stored in the pinpointing device or in an image captured by a camera of the pinpointing device, which can facilitate finding the precise location of the cable fault. Therefore, if two target locations for a possible fault location are displayed after measuring at the first and second positions of the pinpointing device, the user can immediately identify which of the target locations the actual precise fault location must be. If only one target location is displayed on the display after measuring at the first and second current positions of the pinpointing device, or after measuring at the first, second, and third current positions of the pinpointing device, the consistency of this target location with the stored cable course can be checked. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Further advantages and details of the present invention are explained below with the aid of the accompanying drawings. In the drawings:

[0019] Figure 1 A schematic diagram showing precise positioning;

[0020] Figure 2 A schematic diagram showing a precise positioning device;

[0021] Figure 3 A diagram is shown for explaining a first step for determining a possible fault location of a cable fault;

[0022] Figure 4 The basis for the second step of determining the exact fault location is shown Figure 3 pictorial representation;

[0023] Figure 5 a diagram showing a display device of a precise positioning device;

[0024] Figure 6 Shown in other measurement situations according to Figure 3 pictorial representation;

[0025] Figure 7 Showing the basis for the modified embodiment of the present invention Figure 2 Schematic diagram;

[0026] Figure 8 A diagram showing a display device of the precise positioning device according to this modified embodiment of the present invention;

[0027] Figure 9The basis for explaining possible calculation methods is shown Figure 3 icon. DETAILED DESCRIPTION

[0028] The method according to the invention for precise positioning is described below with reference to the accompanying drawings. Figure 1 A schematic diagram shows an underground cable 1 for transmitting electrical energy. The cable can be a low-voltage cable (up to 1 kV), a medium-voltage cable (1 kV to 60 kV), or a high-voltage cable (>60 kV, for example, 110 kV, 220 kV, or 380 kV). At a defect location f, the cable has a cable fault, particularly a high-resistance cable fault or an intermittent cable fault. The approximate location u of the cable fault is determined using known pre-positioning (rough localization).

[0029] To precisely locate (or relocate) a cable fault, a surge voltage pulse 3 is fed into the cable 1 using a surge voltage generator 2 connected to the cable. For example, a surge voltage pulse can be fed every three seconds. The interval between each surge voltage pulse can also have different values, but is preferably between 1 second and 10 seconds.

[0030] The magnitude of the surge voltage pulse may also depend on the type of cable being inspected. Typically, the magnitude of the surge voltage pulse is above 1 kV, for example, in the range of 2 to 5 kV for high-voltage cables. For medium- and high-voltage cables, the magnitude of the voltage pulse is typically above 5 kV, for example, in the range of 10 to 40 kV. Preferably, the magnitude of the voltage pulse can be adjusted on the surge voltage generator. Advantageously, the surge voltage generator covers an adjustable range of at least 2 kV to 30 kV, although a larger range is also possible.

[0031] A person 4 who locates a cable fault carries a mobile precise location device 5. In the illustrated embodiment, the precise location device comprises two separate devices, a detection unit 6 and a display unit 7. Data transmission between the detection unit 6 and the display unit 7 occurs wirelessly, for example, using Bluetooth, but can also be done via a wired connection.

[0032] The detection unit 6 has a microphone 8 (which can also be called a "seismometer") and an electromagnetic sensor 9. The signals emitted by the microphone 8 and the electromagnetic sensor 9 are detected by an analog circuit, A / D converted and sent to the microprocessor unit. Figure 21 is schematically shown as an electronic signal processing unit 10. In addition, data is transmitted to a receiver 12 of the display unit 7 by means of a transmitter 11. The received data is analyzed in a microprocessor unit 13 and the display device 14 is controlled by the microprocessor unit 13. A microprocessor 15 and a memory 16 are schematically indicated in the microprocessor unit 13. The microprocessor unit 13 usually has Figure 2 Other components not shown.

[0033] The detection units 6 may also be collectively referred to as "geophones."

[0034] Furthermore, the display unit 7 has a GPS receiver 17 connected to the microprocessor unit 13 for receiving GPS signals.

[0035] If data is also to be transmitted from the display unit 7 to the detection unit 6, which is generally expedient, the transmitter 11 and the receiver 12 are each designed as a transceiver unit. In the case of online data transmission, the transmitter 11 and the receiver 12 can also be omitted. Thus, only one microprocessor unit can also be provided in the display unit 7 or in the detection unit 6, which has at least one microprocessor 15 and a memory 16.

[0036] The display unit can be a smartphone or tablet. Commercially available smartphones or tablets can be used, which are configured accordingly. However, the display unit can also be specially designed for this application.

[0037] In a modified embodiment, the detection unit 6 and the display unit 7 can also be connected to form a common device.

[0038] The signal received by the microphone may be output to headphones and / or speakers so that the user obtains acoustic feedback.

[0039] To precisely locate cable faults, a surge voltage generator 2 is used to feed repetitive surge voltage pulses 3 into the cable 1. Each surge voltage pulse 3 causes a breakdown at the defect location f of the cable 1, thereby generating an acoustic signal in the form of an acoustic pulse 18. This acoustic pulse 18 propagates in all directions in the ground 19 surrounding the cable 1.

[0040] If a surge voltage pulse 3 fed into the cable 1 passes through the area beneath the mobile pinpoint locating device 5, the resulting electromagnetic signal is detected as an electromagnetic pulse by the electromagnetic sensor 9. This detected electromagnetic pulse is used by the microprocessor unit 13 as a first trigger, which initiates the time measurement. If the microphone 8 receives an acoustic pulse 18 caused by the breakdown triggered by the surge voltage pulse and outputs a corresponding signal to the microprocessor unit 13, this is used by the microprocessor unit 13 as a second trigger signal, which ends the time measurement. The distance s1' between the fault location f in the ground of the cable 1 and the current position of the pinpoint locating device 5 is determined based on the time Δt that elapses between the first and second trigger signals. In this case, the travel time of the surge voltage pulse between the current position of the mobile pinpoint locating device 5 and the fault location f, or the propagation time of the electromagnetic pulse detected by the electromagnetic sensor 9 due to the surge voltage pulse, can be ignored because the propagation velocity vA of the acoustic pulse, i.e., the speed of sound waves in the ground 19, is significantly lower. Therefore, the distance s1' is determined as: s1' = vA·Δt.

[0041] This determination of the distance s1 ′ between the actual defect location f of the cable 1 and the current position of the mobile fine positioning device 5 is known and is also referred to as the “coincidence method”.

[0042] The precise fault position p of the cable fault is determined using the precise positioning device 5. The fault position is a position on the ground 20 vertically above the actual defect position f of the cable. Therefore, in a plan view, the precise fault position p coincides with the actual defect position f of the cable.

[0043] Next, excavation work should be performed at the precise fault location p so as to expose the defect location f of the cable 1 .

[0044] With the help of Figure 3 and 4 To describe the determination of the exact fault location p, Figure 3 and 4 It's a floor plan.

[0045] First, at the first current position of the mobile precise positioning device 5, a position measurement value a1 for this current position is detected by means of the GPS receiver 17 of the mobile precise positioning device 5. Furthermore, at this current position of the mobile precise positioning device 5, a distance measurement value s1 of the distance between the precise fault position p and the current position of the precise positioning device 5 is determined. For this purpose, the distance s1' of the actual defect position f of the cable 1 and the current position of the mobile precise positioning device 5 can be approximately taken into account, which distance is determined as described above. This approximation can be sufficient in particular when the distance between the defect position f of the cable 1 and the current position is large. In particular, if the distance measurement value is below a minimum value, the depth value t of the laying depth of the cable 1 can be taken into account (see Figure 1 For example, a typical cable laying depth, such as 0.5 m, can be stored and taken into account for this depth value t. Manual input is also possible. Taking into account the depth value t, a distance measurement value s1 that is more or less smaller than the determined distance s1 ' is determined.

[0046] The minimum value of s1 ′, below which the corrected distance measurement value s1 is determined and taken into account, may be, for example, 1.5 m. Even at larger values of s1 ′, a corrected distance measurement value s1 can be determined and taken into account.

[0047] Subsequently, at a second current position of the mobile precise positioning device, which differs from the first current position, the position measurement value p2 and the distance measurement value a2 are again determined.

[0048] Based on the two position and distance measurements, at least one possible fault location o1, o2 can be determined. The possible fault location o1, o2 lies both on a circle with a center a1 and a radius s1 and on a circle with a center a2 and a radius s2. Figure 3 The figure shows a situation in which the first and second current positions of the precise positioning device, used to determine the position measurements a1, a2 and the distance measurements s1, s2, do not lie on a common straight line. Consequently, the circle with center a1 and radius s1 and the circle with center a2 and radius s2 intersect at two locations, representing possible fault locations o1, o2. The actual precise fault location p lies at one of these two possible fault locations o1, o2.

[0049] In addition, Figure 3 The course of the cable 1 (which may be unknown) is indicated by a dashed line in FIG. Furthermore, the approximate position u of the cable fault, determined in the pre-location method, is shown.

[0050] Next, as in Figure 4As shown in FIG, a position measurement value a3 and a distance measurement value s3 are again determined at a third current position of the fine positioning device that is different from the first and second positions and not lying on a common straight line therewith. Thus, the one of the possible fault locations o1, o2 that lies on the circle with center a3 and radius s3 can be identified as the precise fault location p. Due to possible measurement errors, a permissible deviation can be set within which a possible fault location o1, o2 is always considered to lie on the circle with center a3 and radius s3.

[0051] exist Figure 4 The dotted line in FIG. 1 again indicates the course of the cable 1 and the approximate location of the cable fault.

[0052] This possible fault position o1 , which corresponds to the precise fault position p, is shown as a target position z on the display device 14 of the mobile precise positioning device 5 , more precisely on a map previously stored on the precise positioning device 5 .

[0053] A map is a two-dimensional map, but it can also be a satellite image. Three-dimensional maps are also possible.

[0054] Therefore, the map previously stored in the precise positioning device includes at least the surroundings of the approximate location u of the cable fault determined in the pre-positioning method (the map preferably includes at least a range of 500 m around the approximate location u of the cable fault determined in the pre-positioning method). The map can be stored in the precise positioning device 5 or can also be downloaded from the Internet for the respective application. Figure 5 As can be seen in FIG. 2 , the street direction 21 is shown on the map.

[0055] The user can thus proceed directly to the indicated target location z. Further measurements, such as sound intensity level measurements, can also be performed there in order to verify the exact fault location p.

[0056] The current position of the mobile precise positioning device 5 , corresponding to the position measurement value a3 , is preferably also shown on the map. The approximate position u of the cable fault, determined by pre-positioning, can also be shown.

[0057] Furthermore, if the geographical orientation of the cable 1 (= the laying path of the cable 1) is known and stored in the precise positioning device, the geographical orientation of the cable 1, i.e. the plan view of the cable orientation, can be shown on the map. For this purpose, the existing geographical data of the cable orientation can be stored in the memory 16 beforehand, for example by transferring it from a GIS database. The cable orientation can also be input by the user. Figure 5 In the diagram, the cable route is indicated by a dotted line.

[0058] The display of the cable path can additionally verify the correct position of the target position z, ie, the correct position of the precise fault position p. This also facilitates the determination of the position at which the measurement was performed (ie, the determination of the position measurement values a1, a2, a3).

[0059] After the measurement at the position of the fine positioning device corresponding to the position measurement values a1, a2, a display similar to the one shown on the display device 14 of the mobile fine positioning device 5 can already be displayed. Figure 5 . Then, two target positions z corresponding to possible fault locations o1 and o2 are also shown. Preferably, the current position corresponding to the position measurement value a2 is also shown. Thus, the user can already determine where the possible fault locations o1 and o2 are located before performing the third measurement. If the cable path is also shown on the display, the user can determine which of the two target positions z shown corresponds to the exact fault location p after the second measurement.

[0060] Figure 6 The following shows the situation resulting from a measurement performed at a position corresponding to the position measured values a1, a2, when the position measured values a1, a2 are located, in particular, by chance, on a straight line g, which also passes through the exact fault position p. The circle with center a1 and radius s1 and the circle with center a2 and radius s2 have only one point in common, resulting in only one possible fault position o1, which corresponds to the exact fault position p. A second measurement can then be performed directly after the second measurement. Figure 5 (wherein the position of the precise positioning device corresponds to the position measurement value a2).

[0061] The method according to the invention therefore enables a very time-saving and reliable exact positioning for the user.

[0062] With the help of Figure 7 and 8 A modified embodiment of the invention is explained below. Apart from the differences described below, this modified embodiment corresponds to the previously described embodiment and its description applies accordingly together with the described possible modifications.

[0063] The difference from the previously described embodiment is that, in order to display at least one target position z on the display device 14 of the mobile precise positioning device 5, the user uses the camera 23 of the mobile precise positioning device 5 to take an image (photo) of the surroundings of the approximate location u of the cable fault and the at least one target position z is displayed in this image, see Figure 8Thus, at least one target position z of the actual fault location is inserted into the real image captured by the camera of the precise positioning device. If the target position z (or at least one of the target positions z) should be outside the image captured by the camera, this is signaled to the user accordingly.

[0064] This modified embodiment of the present invention can also be combined with the previously described embodiment of the present invention, in which case the user can select whether a map or an image recorded by the camera is displayed in the display device.

[0065] Different further modifications of the invention are conceivable and possible. Thus, for example, the analysis described above by the microprocessor unit 13 can also be carried out completely or partially in the microprocessor unit of the detection unit 6 .

[0066] The GPS receiver 17 can also be arranged in the detection unit 6 .

[0067] The electromagnetic sensor 9 may also be arranged in the display unit 7 . Then, the detection unit 6 may have only the microphone 8 .

[0068] As already mentioned, a smartphone or tablet computer can also be used as display unit 7. Display unit 7 can also have two or more separate devices. Thus, display unit 7 can have a first device that displays the distance to the cable defect location and / or the sound intensity of the noise (typically) caused by a breakdown, and a second device that can be, for example, a smartphone or tablet computer that displays (at least one) target location on a map or in an image captured by a camera.

[0069] The calculation scheme for determining possible fault locations o1 and o2 is Figure 9 The angle α can be directly determined (using the law of cosines) from the distance measurement values s1, s2 and the distance a between the position measurement values p1, p2, thereby obtaining the possible fault locations o1, o2. The calculation can be repeated for a2, a3; s2, s3, thus obtaining the precise fault location p as one of the two possible fault locations o1, o2.

[0070] Reference Signs List

[0071] 1 cable

[0072] 2 Surge voltage generator

[0073] 3 Surge voltage pulse

[0074] 4 people

[0075] 5 Mobile precision positioning device

[0076] 6 Detection Unit

[0077] 7 Display unit

[0078] 8 microphones

[0079] 9 Electromagnetic sensor

[0080] 10 Electromagnetic signal processing unit

[0081] 11 Transmitter

[0082] 12 Receivers

[0083] 13 Microprocessor Unit

[0084] 14 Display device

[0085] 15 Microprocessor

[0086] 16 Memory

[0087] 17 GPS receiver

[0088] 18 Acoustic Pulse

[0089] 19 Land

[0090] 20 Ground

[0091] 21 Street Direction

[0092] 22 Electromagnetic Pulse

[0093] 23 cameras

[0094] a1, a2 Position measurement values of the current position of the precise positioning device

[0095] f Cable defect location

[0096] g straight line

[0097] o1, o2 possible fault locations

[0098] p Precise fault location

[0099] s1, s2 distance measurement values

[0100] t depth value

[0101] u Approximate location of cable fault

[0102] z target position

Claims

1. A method for precisely locating a cable fault in an underground cable (1) for transmitting electrical energy, wherein, in order to determine the exact fault position (p) of the cable fault, based on the approximate position (u) of the cable fault previously determined by pre-positioning, the respective distance of the defect position (f) of the cable (1) from the respective current position of the mobile precise positioning device (5) is determined by means of a mobile precise positioning device (5), characterized in that At a first and a second different current position of the precise positioning device (5), first and second position measurement values (a1, a2) for the respective current position of the precise positioning device (5) are determined by means of a GPS receiver (17) of the precise positioning device (5), and first and second distance measurement values (s1, s2) for the respective distances of the precise fault location (p) from the respective current position of the mobile precise positioning device (5) are determined, and a circle is drawn at the first position measurement value (a1) with the first distance measurement value (s1) as radius and at the second position measurement value (a2) with the second distance measurement value (s2) as radius, and the intersection of the two circles is the possible fault location (o1, o2), and at least one target location (z) is displayed on a display device (14) of the precise positioning device (5) in a map of the environment of the approximate position (u) of the cable fault stored in the precise positioning device (5) or in an image recorded by a camera (23) of the mobile precise positioning device (5), the target location corresponding to at least one of the possible fault locations (o1, o2) determined in this way.

2. The method according to claim 1, characterized in that In order to determine the respective distance measurement values (s1, s2) for the distance of the precise fault location (p) from the respective current position of the mobile precise positioning device (5), surge voltage pulses (3) are fed into the cable (1) and the mobile precise positioning device (5) measures the time difference (Δt) between an electromagnetic pulse (22) caused by one of the surge voltage pulses and detected by the electromagnetic sensor (9) of the precise positioning device (5) and an acoustic pulse (18) caused by a breakdown triggered by the surge voltage pulse in the event of a cable fault and detected by the microphone (8), and the precise positioning device (5) determines the respective distance measurement values (s1, s2) based on the time difference (Δt).

3. The method according to claim 2, characterized in that In order to determine the corresponding distance measurement values (s1, s2), the depth value (t) of the laying depth of the cable (1) is taken into account at least below the minimum value of the value (s1') obtained by the time difference of the distance between the defect position (f) of the cable (1) and the corresponding current position of the mobile precise positioning device (5), so that the distance measurement value (s1, s2) of the distance between the precise fault position (p) of the cable fault located on the ground vertically above the defect position (f) and the current position of the mobile precise positioning device (5) is smaller than the value (s1') obtained by the time difference of the distance between the defect position (f) and the corresponding current position of the mobile precise positioning device (5).

4. The method according to any one of claims 1 to 3, characterized in that The at least one possible fault location (o1, o2) is determined without taking into account the course of the cable (1) with reference to the plane.

5. The method according to any one of claims 1 to 3, characterized in that At a third current position of the precise positioning device (5) that is different from the first and second current positions, the mobile precise positioning device (5) determines a third position measurement value (a3) for the current position of the precise positioning device (5) and a third distance measurement value (s3) for the distance of the precise fault position (p) from the current position of the mobile precise positioning device (5), wherein the third current position and the first and second current positions of the precise positioning device (5) are not located on a common straight line, and using the third position measurement value (a3) and the third distance measurement value (s3) it is determined which of the two possible fault positions (o1, o2) of the precise fault position (p) corresponds to the precise fault position (p), by determining at which of the two possible fault positions (o1, o2) of the precise fault position (p) the distance from the third current position of the precise positioning device (5) corresponds to the third distance measurement value (a3), and displaying the precise fault position (p) thus determined on a display device (14) of the precise positioning device (5) on a map or in an image recorded by a camera (23) as a target position (z).

6. The method according to any one of claims 1 to 3, characterized in that Data transmission between a detection unit (6) of a mobile precise positioning device (5) having a microphone (8) and an electromagnetic sensor (9) and a display unit (7) of the mobile precise positioning device (5) having a display device (14) takes place wirelessly.

7. The method according to any one of claims 1 to 3, characterized in that The detection unit (6) has a smartphone or a tablet or is formed by a smartphone or a tablet.

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