RU2703195C1 - Method of determining distance to a point of reflection in an electrical conductor - Google Patents

Abstract

FIELD: measurement technology.

SUBSTANCE: invention relates to a method of determining distance (L) to a point of reflection in electrical conductor (21). According to the invention, it is provided that the electric supplied signal (E) modulated in frequency and/or phase is generated, the supplied signal (E) is input at measurement point (MST) into conductor (21), reflected to measurement point (MST) signal, called measurement signal (M), is measured in measuring point (MST), and based on frequency (f) and/or phase of measurement signal (M) and based on actual frequency (f) and/or phase of transmitted signal (E) at time of arrival of measurement signal (M), determining the distance to reflection point value (W) of distance. Frequency (f) of the transmitted signal (E) is increased or decreased within range of 30–500 kHz within a time interval of 1 s and/or the supplied signal (E) is introduced into conductor (21) with power of 50–150 W.

EFFECT: method is proposed for determination of distance to point of reflection in electric conductor.

20 cl, 8 dwg

Description

The invention relates to a method and apparatus for measuring distance in order to determine the location of reflection, in particular a malfunction, in an electrical conductor.

Malfunctions sometimes occur in overhead power lines and underground cables, for example, due to a broken line, an interrupted underground cable or a short circuit to a line or a short to ground. This can lead, in particular with very long lines, to a relatively long interruption of current, when it is not known where the fault occurred.

Along with current-carrying lines in which a fault can be recognized at least instantaneously, lines without current are also of interest, for example, in a special return wire in high voltage DC transmission lines, which are usually not energized.

The following methods are known for detecting and localizing faults in lines and cables:

Option 1: The simplest type of inspection is visual inspection by maintenance personnel. This method with long lines requires a lot of time.

Option 2: Another option for measuring the position of a fault is the so-called TDR-Puls method. In this case, an electric pulse is supplied to the line. At the fault location, the impulse is reflected to the feed location and can be received there again. Based on the pulse transit time, a conclusion can be made about the position of the malfunction. The ulsPuls-Echo-Electrode Line Monitoring System PEMOʺ from Siemens AG is based on this principle of operation.

Option 3: Another option for measuring distances is the so-called aultFault Passageʺ indicators, which are mounted in overhead lines at certain distances from each other. In the event of a malfunction, the indicators show between which indicators the malfunction lies. Siemens instruments of the FSI series are based on this method.

Option 4: In addition, if a malfunction occurs, a traveling wave can be detected at both ends of the line / cable. If both detection devices at both ends of the line / cable are sufficiently synchronized, then it is possible to draw a conclusion about the type of malfunction using the measured data.

The basis of the invention is the task of creating an accurate method for determining the distance to the place of reflection in an electrical conductor.

This problem is solved, according to the invention, using a method with the characteristics of paragraph 1 of the claims. Preferred embodiments of the method according to the invention are indicated in the dependent claims.

In accordance with this, an electric signal fed in frequency and / or phase is generated, the applied signal is introduced at the measurement site into the conductor, the signal reflected at the measurement site, called the subsequent measurement signal, is measured at the measurement site, and based on the frequency and / or phase measuring signal and based on the actual frequency and / or phase of the supplied signal at the time of arrival of the measuring signal, a distance value is determined that indicates the distance to the reflection site.

As will be explained in more detail below, the method allows to recognize, depending on the implementation, a malfunction in the conductor and / or to determine the distance to the malfunction, regardless of whether the malfunction is recognized within the method or is already recognized using another external method.

Compared with the above option 1, a significant advantage of the method according to the invention is that it is possible to very quickly determine the location of the malfunction and without personnel costs.

Compared with the above option 2, the advantage of the method according to the invention is that much more energy can be introduced into the line than is possible with a single pulse. Due to this, the signal-to-noise ratio is increased, and, in addition, it is possible to control significantly longer lines than in the above embodiment 2, using only one system.

Compared with options 3 and 4, the method according to the invention can also be used in lines that do not conduct current. There is also no need to measure at the point in time at which the malfunction occurs. In addition, installation and maintenance costs are lower since the measuring device needs to be installed in only one place, and not in two or more places.

In addition, it is preferable that using the method according to the invention, it is possible to evenly distribute the input energy over the width of the range or to exclude certain frequency ranges that cannot be used, for example, on the basis of regulatory requirements.

Another advantage of the method according to the invention is that it is relatively insensitive to interference signals from pulsed interference sources, such as, for example, AC / DC converters.

According to one preferred embodiment, it is provided that the distance value is compared with a reference value indicating the distance to the known end of the conductor, and a fault signal is generated when the distance value is less than the reference value.

In the presence of a fault signal, a distance value is preferably output as the distance value to the fault.

According to another preferred embodiment, it is provided that after recognizing a fault in the conductor using an external fault recognition method, and if there is an external fault signal, a distance value is determined, and it is output as a distance value to the fault.

Preferably, when a frequency-modulated signal is generated as the supplied signal so that the frequency of the supplied signal changes in time in accordance with a predetermined change function, the frequency of the measurement signal reflected from the meta-malfunction is measured, and based on the actual frequency of the supplied signal at the time of arrival of the measurement signal signal, the distance value indicating the distance to the place of reflection is determined.

The change function is preferably a step or sawtooth function. In other words, as a frequency-modulated supplied signal, a supplied signal is preferably created with a stepwise or sawtooth frequency change.

The electrical conductor is preferably an overhead line or cable for transmitting energy. It is especially preferred when the method is used in the return wires of high voltage direct current transmission lines. In other words, it is also preferable when the supplied signal is introduced into the return wire of the high voltage direct current transmission line, which is de-energized in good working condition. Controlling the operational readiness of a return wire without current is an advantage, since if there is a possible malfunction in the high voltage direct current transmission system, it is necessary to switch to this wire.

 Preferably, a frequency-modulated signal with a constant amplitude is introduced into the wire as a supplied signal.

The frequency of the supplied signal preferably varies in the range between 1 kHz and 1 MHz, while the frequency change in time, respectively, the derivative of the frequency in time is constant.

The distance value is preferably determined by the formula

W =

where V is the propagation velocity of the measuring signal in the conductor, W is the distance value, ׀ Δf ׀ is the difference between the frequencies of the frequency of the received measuring signal and the actual frequency of the supplied signal at the time of arrival of the measuring signal, and df / dt is the time derivative of the frequency of the supplied signal.

The frequency of the supplied signal is preferably increased or decreased in the range between 30 kHz and 500 kHz within a time interval of 1 s.

The supplied signal is introduced into the conductor, preferably with a power between 50 W and 150 W.

The reflected measurement signal and the supplied signal are preferably mixed in the mixer, and a distance value is preferably determined based on the frequency of the mixing signal.

It is also preferable when the supplied signal is supplied to the conductor through the transmitting and receiving separation filter, and the reflected measuring signal is received through the transmitting and receiving separation filter.

In another embodiment of the method, it is provided that the supplied signal is generated using the output signal of the digital signal generator, turned on after the signal generator of the digital-to-analog converter and turned on after the digital-to-analog converter of the amplifier, the reflected measuring signal is supplied to the analog-to-digital converter, and using the output the signal of the analog-to-digital converter and the digital output signal generated by the digital signal generator, the distance value is determined.

Preferably, when the reflected measurement signal is first damped by a damping element, and the damped signal is supplied to an analog-to-digital converter.

The invention further relates to a distance measuring device for determining a distance to a reflection site, in particular a malfunction, in an electrical conductor. A distance measuring device according to the invention is characterized in that a signal source is provided for generating a frequency-modulated and / or phase-modulated electrical signal, a receiving unit for measuring a measurement signal reflected from the reflection location to the measurement location, and a processing unit which frequency and / or phase of the measuring signal and based on the actual frequency and / or phase of the supplied signal at the time of arrival of the reflected measuring signal determines The present display range value.

The signal source is preferably configured to produce a frequency-modulated supplied signal as a supplied signal by changing the frequency of the supplied signal in time in accordance with a predetermined change function.

The processing unit is preferably configured to determine a distance value based on the frequency of the measurement signal and based on the actual frequency of the supplied signal at the time of arrival of the measurement signal.

The distance measuring device can preferably transmit and receive at the same time. In other words, the signal source can supply the supplied signal, while the receiving unit receives the measuring signal, and the processing unit evaluates it.

The processing unit preferably also evaluates the phase position of the measuring signal and, based on the phase position, determines whether the fault is a short circuit or the open end of the conductor.

The distance measuring device preferably comprises a device for matching impedances and a coupling capacitor for inputting the supplied signal and outputting the reflected measurement signal from the conductor.

The following is a more detailed explanation of the invention based on exemplary embodiments with reference to the accompanying drawings, which show, by way of example:

FIG. 1 is a power transmission installation in which a distance measuring device is connected to an overhead line, according to one embodiment of the invention;

FIG. 2 is an exemplary embodiment of a distance measuring device that is used in a power transmission apparatus according to FIG. one;

FIG. 3 and 4 are examples of changes in frequency over time to explain the principle of operation of the distance measuring device according to FIG. 2;

FIG. 5 is another exemplary embodiment of a distance measuring device that is suitable for installing a power transmission according to FIG. one;

FIG. 6 is another exemplary embodiment of a power transmission installation in which a distance measuring device is connected to an overhead line;

FIG. 7 is an example embodiment of a device for measuring a distance in which exclusively monitoring of a malfunction is carried out and, possibly, a malfunction signal is issued; and

FIG. 8 is an example embodiment of a device for measuring a distance in which both monitoring of a malfunction is carried out and, possibly, a malfunction signal is output, and in the event of a malfunction, a distance value is output, i.e. distance to the fault.

In the figures, for clarity, identical or similar components are everywhere denoted by the same reference numerals.

In FIG. 1 shows an energy transmitting apparatus 10, which comprises an overhead line 20. At the measurement site MST, a distance measuring device 30 is connected to one wire 21 of the overhead line.

There is a malfunction in overhead line 20: wire 21 is interrupted at location FS of the malfunction. The distance between the distance measuring device 30, respectively, the measuring location MST, and the fault location FS, i.e. the distance to the fault is indicated in FIG. 1 by L.

In FIG. 2 shows an exemplary embodiment of a distance measuring device 30 that can be used in an energy transmitting installation 10, according to FIG. 1. The distance measuring device 30 according to FIG. 2, comprises a signal source 31, a receiving unit 32, a processing unit 33, and a transmit and receive separation filter 34.

 The signal source 31 has an analog signal generator 310 and an amplifier 311 included behind it. The amplifier 311 on the output side is connected to the transmitting and receiving separation filter 34 and to the receiving unit 32.

The receiving unit 32 includes a mixer 320 and a measuring module 321. The mixer 320 on the input side is connected to a transmitting and receiving separation filter 34 and an amplifier 311 and on the output side to a measuring module 321.

The distance measuring device 30 according to FIG. 1 preferably works as follows:

The signal generator 310 generates a frequency or phase modulated electrical output signal S, which is amplified by an amplifier 311 and, in the form of a frequency and / or phase modulated electrical signal E, is supplied through a transmit and receive isolation filter 34 to a wire 21 of an overhead line 20, according to FIG. 1. In addition, the electrical input signal E enters the mixer 320 of the receiving unit 32.

Modulated in frequency and / or phase, the electrical signal E is transmitted through the wire 21 to the fault location FS and is reflected back to the transmit and receive isolation filter 34. The reflected measurement signal is indicated in FIG. 2 by M. The reflected measurement signal M is sent from the transmit and receive isolation filter 34 to the mixer 320, which mixes the reflected measurement signal M with the supplied signal E.

In the following, it is taken as an example that the supplied signal E is a frequency-modulated supplied signal whose frequency increases linearly in time, so that a sawtooth function in time is formed.

In FIG. 3 shows the course of the frequency response f of the supplied signal E and the frequency of the reflected signal M as a function of time. It can be seen that there is a difference Δf of frequencies between the frequency f of the supplied signal E and the frequency of the reflected measurement signal M. The difference Δf of frequencies is caused by the fact that the reflected measurement signal M arrives at the mixer 320 with a time delay, since it, unlike directly supplied to the the mixer 320 of the electrical signal E, has already passed through the wire 21 to the place FS malfunction and vice versa. Travel time is shown in FIG. 3 difference Δf frequencies.

The mixer 320 creates on the output side a mixing signal MS, the frequency of which corresponds to the frequency difference Δf between the supplied signal E and the reflected measuring signal M. Thus, the mixing signal MS, respectively, its frequency Δf, is a measure of the time it takes for the supplied signal E to reach the fault location FS and back, and thereby a measure of the distance L between the distance measuring device 30 and the location FS of the malfunction.

The mixing signal MS is measured by the measuring module 321, which provides the frequency value F on the output side. The frequency value F indicates the frequency Δf of the mixing signal and thereby the frequency difference Δf between the supplied signal E and the reflected measuring signal M.

The frequency value F is supplied to the processing unit 33, which, using the frequency difference value Δf indicating the frequency value F determines the distance indicating the distance L, the distance value W, preferably as follows:

W =

where V is the propagation velocity of the measuring signal in the conductor, W is the distance value, ׀ Δf ׀ is the difference in the frequency of the received measuring signal and the actual frequency of the supplied signal T at the time of arrival of the measuring signal, and df / dt is the derivative of the frequency f with time t supplied E. signal

Thus, the distance measuring device 30 determines the distance value W, respectively, the distance L, to the fault based on the frequency difference Δf and the slope df / dt shown in FIG. 3 sawtooth function.

Alternatively or additionally, the distance measuring device 30 can check whether a malfunction has occurred in the wire 21. For example, the distance measuring device 30 can measure the distance to the point of reflection for the received reflected measurement signal M to form a distance value W and compare this a distance value W with a distance to a known end of the wire 21 of the reference value Lmax. When the distance value W is smaller, in particular significantly less than the reference value Lmax (for example, it is only 95% of the reference value Lmax), it can give a fault signal SF.

In FIG. 7 shows an embodiment of a distance measuring device 30 in which fault monitoring is carried out exclusively and, if necessary, only a fault signal SF is output; in FIG. 8 shows an embodiment of a distance measuring device 30 in which both fault monitoring is performed and, if necessary, a fault signal SF is output, and in the event of a fault, a distance value W is additionally generated, i.e. distance to the fault.

As shown in FIG. 3, 7 and 8, the increase in the frequency up is technically limited, then the frequency response over time is preferably sawtooth or triangular. For example, the signal generator 310 may, upon reaching the upper limit frequency, switch to the lower initial frequency, thereby providing a sawtooth path, as shown by way of example in FIG. four.

In connection with FIG. 2-4 and 7-8, the determination of the distance value W for a frequency-modulated electrical input signal E was explained as an example; accordingly, the distance value W can be determined based on the frequency modulated and / or phase modulated electrical signal E, by evaluating the frequency difference and / or phase difference between the supplied signal E and the reflected measurement signal M.

In FIG. 5 shows another exemplary embodiment of a distance measuring device that can be used in the power transmission installation 10 according to FIG. one.

In contrast to the exemplary embodiment of FIG. 2, the distance measuring device 30 according to FIG. 5, operates without an analog transmit and receive isolation filter 34.

The distance measuring device 30 according to FIG. 5, comprises a signal source 41, a receiving unit 42, and a processing unit 43. The signal source 41 has a digital signal generator 410, a digital-to-analog converter 411, and an amplifier 412. The processing block 42 is formed by a damping link 420, an analog-to-digital converter 421, and a measurement module 422. The output of the measuring module 422 and the output of the digital signal generator 410 are each connected to the processing unit 43.

The distance measuring device 30 according to FIG. 5 preferably works as follows:

The digital signal generator 410 generates a digital output signal S modulated in frequency and / or phase on the output side, which is converted into an analog signal using a digital-to-analog converter 411 and then amplified by an amplifier 412. The signal output from an amplifier 412 forms an electric signal E, which is fed into the wire 21 of the overhead line 20 according to FIG. one.

Reflected from the fault location FS, the measurement signal M enters through the damping link 420 and the analog-to-digital converter 421 to the processing unit 43.

The processing unit 43 determines digitally, for example, the frequency difference between the output signal S generated by the digital signal generator 410 and the digital measurement signal Md provided by the measuring module 422, and generates a distance value W, preferably in accordance with the formula

W =

where V is the propagation velocity of the measuring signal in the conductor, W is the distance value, ׀ Δf ׀ is the frequency difference between the frequency of the measuring signal Md and the actual frequency of the supplied signal E at the time of arrival of the measuring signal Md, and dt / df is the time derivative t frequency f of the supplied signal E.

A digital signal generator 410, a processing unit 43, and a measurement module 422 may be formed by a digital signal processor DSP.

Alternatively or additionally, a distance recognition device 30 may also be provided with fault recognition, as explained above with respect to FIG. 7 and 8; in this regard, reference is made to the above calculations of FIG. 7 and 8.

In FIG. 6 shows an embodiment of a distance measuring device 30 according to FIG. 1, in which the distance measuring device 30 is connected not directly to the wire 21, but via the coaxial cable 60, the impedance matching unit 70 and the coupling capacitor 80. Otherwise, the explanations in connection with FIG. 1-5 and 7 and 8.

With reference to FIG. 1-8 above was an explanation of an example implementation for determining the distance to the fault on the example of a single wire 21; accordingly, it is possible to determine the distance to the malfunction in other wires of the energy transmitting installation 10.

Explained with reference to FIG. 1-8 exemplary embodiments can preferably be combined with power line systems. You can also determine if a switch or splitter on a line is closed or open, since an open switch / splitter reflects the input signal just like a broken wire.

Explained by way of example with reference to FIG. 1-8, embodiments can preferably be used to control wires and cables for transmitting high-voltage direct current, in particular, to control dedicated return wires and ground lines that do not conduct current in normal operating condition (lines from a high-voltage direct current station to the ground point) . Monitoring the readiness for use of the return wire is preferable, since in the event of a possible malfunction in the high-voltage DC system, switching to this wire may be necessary.

Although the invention has been shown and explained in detail using exemplary embodiments, the invention is not limited to the disclosed examples, and other options may be derived by those skilled in the art without departing from the scope of protection of the invention.

List of items

10 Installation for energy transfer

20 Overhead line

21 Wire

30 Distance measuring device

31 Source

32 receiving unit

33 Processing unit

34 Transmit and receive separation filter

41 Source

42 receiving unit

43 Processing unit

60 coaxial cable

70 Impedance matching device

80 coupling capacitor

310 signal generator

311 Amplifier

320 mixer

320 measuring module

410 signal generator

411 Digital to Analog Converter

412 Amplifier

420 Damping Link

421 Analog to Digital Converter

422 measuring module

DSP Digital Signal Processor

E Signal output

f Frequency

F Frequency Value

FS Fault Location

L Distance to fault

Lmax Reference value

M Measuring signal

Md digital measuring signal

MS Mixing Signal

MST Measurement Location

S Output

SF Alarm

t time

W distance value

Δf Frequency difference

Claims (48)

1. The method of determining the distance (L) to the reflection in the electrical conductor (21), and - generate a modulated frequency and / or phase electrical signal (E), - the supplied signal (E) is introduced at the location (MST) of the measurement into the conductor (21), - the signal reflected to the location (MST) of the measurement, referred to in the subsequent measurement signal (M), is measured in the measurement location (MST) and - based on the frequency (f) and / or phase of the measuring signal (M) and on the basis of the actual frequency (f) and / or phase of the supplied signal (E) at the time of arrival of the measuring signal (M), a distance value (W) indicating distance to the place of reflection, - moreover, the frequency (f) of the supplied signal (E) is increased or decreased in the range between 30-500 kHz within a time interval of 1 s, and / or - the supplied signal (E) is introduced into the conductor (21) with a power between 50-150 watts. 2. The method according to p. 1, characterized in that - the value (W) of the distance is compared with a reference value (Lmax) indicating the distance to the known end of the conductor (21), and - generate a fault signal (SF) when the distance value (W) is less than the reference value (Lmax). 3. The method according to p. 2, characterized in that in the presence of a fault signal (SF) give the value (W) of the distance as the value of the distance to the fault. 4. The method according to any one of paragraphs. 1-3, characterized in that after recognizing a malfunction in the conductor using an external method for recognizing a malfunction, and if there is an external malfunction signal, the distance value (W) is determined and given as the distance value to the malfunction. 5. The method according to any one of paragraphs. 1-4, characterized in that - as a supplied signal (E), a frequency modulated signal is generated due to the fact that the frequency (f) of the supplied signal (E) changes in time in accordance with a predetermined change function, - measure the frequency (f) of the measurement signal (M) reflected from the reflection to the measurement location (MST), and - based on the frequency (f) of the measuring signal (M) and on the basis of the actual frequency (f) of the supplied signal (E) at the time of arrival of the measuring signal (M), a distance value (W) indicating the distance to the reflection point is determined. 6. The method according to p. 5, characterized in that - the change function is a step function or sawtooth function, and - as a modulated frequency of the supplied signal (E) generate the supplied signal (E) with a stepped or sawtooth course of the frequency response. 7. The method according to any one of paragraphs. 1-6, characterized in that the supplied signal (E) is fed into the return wire of the high voltage direct current transmission line, which is de-energized in good working condition. 8. The method according to any one of paragraphs. 1-7, characterized in that the frequency modulated signal with a constant amplitude is introduced into the conductor (21) as a supplied signal (E). 9. The method according to any one of paragraphs. 1-8, characterized in that the frequency (f) of the supplied signal (E) is changed in the range between 1 kHz and 1 MHz, while the change in frequency (f) in time, respectively, the derivative of frequency (f) in time, is constant. 10. The method according to any one of paragraphs. 1-9, characterized in that the value (W) of the distance is determined by the formula $$W=\frac{V\cdot |\; |\; |\Delta f|\; |\; |}{2\cdot \left(df/dt\right)}$$

where V is the propagation velocity of the measuring signal in the conductor, W is the distance value, ׀ Δf ׀ is the magnitude of the frequency difference between the frequency (f) of the received measuring signal (M) and the actual frequency (f) of the supplied signal (E) at the time of arrival of the measuring signal (M), and df / dt is the derivative of the frequency (f) of the supplied signal (E) in time. 11. The method according to any one of paragraphs. 1-10, characterized in that the reflected measuring signal (M) and the supplied signal (E) are mixed in the mixer (320) and the distance value (W) is determined based on the frequency (f) of the mixing signal (MS). 12. The method according to any one of paragraphs. 1-11, characterized in that - the supplied signal (E) is supplied to the conductor through the transmitting and receiving separation filter (34), and - the reflected measuring signal (M) is received through the transmitting and receiving separation filter (34). 13. The method according to any one of paragraphs. 1-12, characterized in that the supplied signal (E) is generated using the output signal (S) of the digital signal generator (410), turned on after the digital-to-analog converter (411), and turned on after the digital-to-analog converter (411) 411) amplifier (412), - a reflected measuring signal (M) is supplied to an analog-to-digital converter (421), and - using the output signal of the analog-to-digital converter (421) and the digital output signal (S) created by the digital signal generator (410), the distance value (W) is determined. 14. The method according to p. 13, characterized in that - the reflected measuring signal (M) is first damped using a damping link (420), and - the damped signal is fed to an analog-to-digital converter (421). 15. The method according to any one of paragraphs. 1-14, characterized in that the electrical conductor (21) is a wire (21) overhead line or cable for transmitting energy. 16. A device (30) measuring the distance to determine the distance (L) to the reflection, in particular a malfunction, in an electrical conductor (21), containing - a source (31, 41) of signals for generating a frequency modulated and / or phase modulated electrical signal (E), - a receiving unit (32, 42) for measuring a measurement signal (M) reflected from a reflection location to a location (MST), and - a processing unit (33, 43), which based on the frequency (f) and / or phase of the measuring signal (M) and on the basis of the actual frequency (f) and / or phase of the supplied signal (E) at the time of arrival of the reflected signal (E ) determines the value (W) of the distance indicating the distance to the place of reflection, moreover, the frequency (f) of the supplied signal (E) increases or decreases in the range between 30-500 kHz within a time interval of 1 s, and / or - the supplied signal (E) is introduced into the conductor (21) with a power between 50-150 watts. 17. The device (30) measuring the distance according to p. 16, characterized in that - the signal source (31, 41) is configured so that it as a supplied signal (E) creates a frequency-modulated supplied signal (E) by changing the frequency of the supplied signal (E) in time in accordance with a predetermined change function, and - the processing unit (33, 43) is made so that it determines the value (W) based on the frequency (f) of the measuring signal (M) and based on the actual frequency (f) of the supplied signal (E) at the time of arrival of the measuring signal (M) ) distance. 18. Device (30) for measuring distance according to any one of paragraphs. 16 or 17, characterized in that the distance measuring device (30) is configured to simultaneously transmit and receive, therefore, the signal source (31, 41) is configured to supply a supplied signal (E), while the receiving unit (32, 42) receives a measuring signal (M), and the processing unit (33, 43) evaluates. 19. The device (30) measuring the distance according to any one of paragraphs. 16-18, characterized in that the processing unit (33, 43) also evaluates the phase position of the measuring signal (M) and, based on the phase position, determines whether the malfunction is a short circuit or the open end of the conductor. 20. The device (30) measuring the distance according to any one of paragraphs. 16-19, characterized in that the device (30) for measuring the distance contains a device for matching impedances (70) and a coupling capacitor (80) for inputting the supplied signal (E) and outputting the reflected measuring signal (M) from the conductor.

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