DE102017214996A1 - Method for determining the distance of a reflection point on an electrical conductor - Google Patents

Abstract

The invention relates u. a. to a method for determining the distance (L) of a reflection point on an electrical conductor (21). According to the invention, it is provided that a frequency- and / or phase-modulated electrical feed signal (E) is generated, the feed signal (E) at a measuring point (MST) is fed into the conductor (21), a signal reflected to the measuring point (MST), below Measured signal (M), measured at the measuring point (MST) and based on the frequency (f) and / or phase of the measuring signal (M) and the current frequency (f) and / or phase of the feed signal (E) at the time of Arrival of the measuring signal (M) a distance of the reflection point indicating distance value (W) is determined.

Description

The invention relates to a method and a distance measuring device for determining the distance of a reflection point, in particular a fault, on an electrical conductor.

On overhead lines and ground cables for power transmission, there are occasional disruptions, for example, because the line is torn off, a ground cable is cut or there is a short circuit or a ground fault. This can lead to a relatively long power interruption, especially with very long lines, if it is not known at which point the error has occurred.

In addition to the current-carrying lines, in which a fault can be detected at least immediately, are also currentless lines of interest, for example, the dedicated return conductor HVDC lines (HVDC: high-voltage DC transmission), which normally leads to no voltage.

• Variante 1: Die einfachste Art der Überprüfung ist eine Sichtüberprüfung durch Wartungspersonal vor Ort. Diese Vorgehensweise ist bei langen Leitungen sehr zeitaufwändig.
• Variante 2: Eine weitere Möglichkeit, die Position eines Fehlers zu messen, bietet das sogenannte TDR-Puls-Verfahren. Hierbei wird ein elektrischer Puls in die Leitung eingespeist. An der Fehlerstelle wird der Puls zum Einspeiseort reflektiert und kann dort wieder empfangen werden. Anhand der Laufzeit des Pulses kann auf die Position des Fehlers geschlossen werden. Das Gerät „Pulse-Echo-Electrode Line Monitoring System PEMO“ (6DD7002-0AA00) der Siemens AG beruht auf diesem Verfahren.
• Variante 3: Eine andere Möglichkeit zur Entfernungsmessung bieten sogenannte „Fault-Passage“-Indikatoren, die an Freileitungen in gewissen Abständen montiert werden. Im Falle eines Fehlers zeigen die Indikatoren an, zwischen welchen Indikatoren der Fehler liegt. Geräte der Siemens FSI-Baureihe beruhen auf diesem Verfahren.
• Variante 4: Des Weiteren ist es möglich, beim Auftreten eines Fehlers die Wanderwelle an den beiden Enden einer Leitung/ eines Kabels zu detektieren. Sind die Detektionsgeräte an den beiden Leitungs-/Kabelenden genau genug synchronisiert, so kann man mit Hilfe der Messdaten auf den Fehlerort schließen.

The following process variants for the detection and localization of cable and cable disorders are known:

• Variant 1: The simplest type of inspection is a visual inspection by on-site maintenance personnel. This procedure is very time consuming with long lines.
• Variant 2: Another possibility to measure the position of a fault is provided by the so-called TDR pulse method. In this case, an electrical pulse is fed into the line. At the fault location, the pulse is reflected to the feed location and can be received there again. Based on the duration of the pulse can be concluded that the position of the error. The "Pulse-Echo-Electrode Line Monitoring System PEMO" (6DD7002-0AA00) from Siemens AG is based on this method.
• Variant 3: Another possibility for distance measurement is provided by so-called "fault-passage" indicators, which are mounted on overhead lines at certain intervals. In case of failure, the indicators indicate between which indicators the error lies. Siemens FSI series devices are based on this procedure.
• Variant 4: Furthermore, it is possible to detect the traveling wave at the two ends of a line / cable when an error occurs. If the detection devices at the two cable ends are synchronized with sufficient accuracy, the measured data can be used to determine the location of the fault.

The invention has for its object to provide a simple, yet accurate method for determining the distance of a reflection point on an electrical conductor.

This object is achieved by a method having the features according to claim 1. Advantageous embodiments of the method according to the invention are specified in subclaims.

Thereafter, the invention provides that a frequency and / or phase modulated electrical feed signal is generated, the feed signal is fed to a measuring point in the conductor, a signal reflected to the measuring point, hereinafter referred to as measuring signal, is measured at the measuring point and based on the frequency and / or phase of the measuring signal and based on the current frequency and / or phase of the feed signal at the time of arrival of the measuring signal, a distance of the reflection point indicating distance value is determined.

As will be explained in more detail below, depending on the embodiment, the method allows the recognition of an error on a conductor and / or the determination of the error distance, be it that the error has been detected in the context of the method or has already been detected by means of another external method.

Opposite the o. G. Variant 1 is a significant advantage of the method according to the invention in that an error can be located very quickly and without personnel expenses.

Compared to variant 2, an advantage of the method according to the invention is that significantly more energy can be brought into the line than is possible with a single pulse. This increases the signal-to-noise ratio, and it is also possible to have significantly longer lines than the o. G. Variant 2 with only one system to monitor.

In comparison to variants 3 and 4, the method according to the invention advantageously also works on lines which do not carry any current. Also, it is not necessary to perform the measurement at the time when the error occurs. Incidentally, the installation and maintenance costs are lower, because a meter must be installed only in one place and not in two or more places.

Incidentally, it is advantageous that in the method according to the invention it is possible to distribute the feed energy of the feed signal uniformly over the bandwidth or certain To avoid frequency ranges which one may not use for regulatory reasons, for example.

Another advantage of the method according to the invention is that it is relatively insensitive to interference signals from pulse-like interferers, such as converters.

According to a preferred embodiment, it is provided that the distance value is compared with a reference value indicating the distance to the known conductor end of the conductor and an error signal is generated if the distance value is smaller than the reference value.

In the presence of the error signal, the distance value is preferably output as the error removal value.

According to another preferred embodiment variant, it is provided that after an error has been detected on the conductor by means of an external error detection method and an external error signal is present, the distance value is determined and outputted as an error removal value.

It is considered advantageous if a frequency-modulated signal is generated as the feed signal by changing the frequency of the feed signal over time according to a predetermined change function, the frequency of the reflected from the reflection point to the measuring point measurement signal is measured and based on the frequency of the received measurement signal and is determined on the basis of the current frequency of the feed signal at the time of arrival of the measurement signal of the distance of the reflection point indicating distance value.

The change function is preferably a ramp function or sawtooth function. In other words, an input signal having a ramp-shaped or sawtooth-shaped frequency characteristic is preferably formed as a frequency-modulated supply signal.

The electrical conductor is preferably a conductor of an overhead line or a cable for power transmission. It is particularly advantageous if the method is used for return conductors of high-voltage direct-current transmission lines. In other words, it is thus advantageous if the feed-in signal is fed into a return conductor, which is de-energized in the fault-free operating state, of a high-voltage direct-current transmission line. It is advantageous to monitor the readiness of the de-energized return conductor, since it may be necessary to switch over to this conductor in the event of a fault in an HVDC system.

As feed signal, a frequency-modulated signal with constant amplitude is preferably fed into the conductor.

The frequency of the feed-in signal is preferably changed in a range between 1 kHz and 1 MHz, wherein the temporal change of the frequency or the derivative of the frequency is constant over time.

wobei V die Ausbreitungsgeschwindigkeit des Messsignals auf dem Leiter, W den Entfernungswert, |Δf| den Betrag der Frequenzdifferenz zwischen der Frequenz des empfangenen Messsignals und der aktuellen Frequenz des Einspeisesignals zum Zeitpunkt des Eintreffens des Messsignals und df/dt die zeitliche Ableitung der Frequenz des Einspeisesignals nach der Zeit bezeichnet.The distance value is preferably determined according to $$W=\frac{V\cdot \left|\Delta f\right|}{2\cdot \left(df/dt\right)}$$

in which V the propagation velocity of the measurement signal on the conductor, W the distance value, | Δf | the amount of the frequency difference between the frequency of the received measurement signal and the current frequency of the feed-in signal at the time of arrival of the measurement signal and df / dt denotes the time derivative of the frequency of the feed-in signal by the time.

The frequency of the feed signal is preferably increased or decreased in a range between 30 kHz - 500 kHz within a period of 1 s.

The feed-in signal is preferably fed into the conductor at a power of between 50 W and 150 W.

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

It is also advantageous if the feed signal is fed into the line via a transmitting and receiving switch and the reflected measuring signal is received via the transmitting and receiving switch.

In a further variant of the method it is provided that the feed signal is generated with a digital output signal of a digital signal generator, a signal generator downstream digital-to-analog converter and a digital-analog converter downstream amplifier, the reflected measurement signal is fed to an analog-to-digital converter and the distance value is determined with the output signal of the analog-to-digital converter and the digital output signal generated by the digital signal generator.

It is advantageous if the reflected measurement signal by means of an attenuator first is attenuated and the attenuated signal is fed to the analog-to-digital converter.

The invention also relates to a distance measuring device for determining the distance of a reflection point, in particular a fault, on an electrical conductor. According to the invention, the distance measuring device is characterized by a signal source for generating a frequency- and / or phase-modulated electrical feed signal, a receiving device for measuring a reflected from the reflection point to the measuring point measurement signal and an evaluation device based on the frequency and / or phase of the measurement signal and the current Frequency and / or phase of the feed signal at the time of arrival of the measurement signal determines a distance of the reflection point indicating distance value.

The signal source is preferably designed such that it generates a frequency-modulated feed-in signal as the feed-in signal by changing the frequency of the feed-in signal over time in accordance with a predetermined change function.

The evaluation device is preferably designed such that it determines the distance value on the basis of the frequency of the measurement signal and on the basis of the current frequency of the feed signal at the time of the arrival of the measurement signal.

The distance measuring device may preferably transmit and receive simultaneously. In other words, the signal source can preferably feed the feed signal, while the receiving device receives the measurement signal and evaluates the evaluation device.

The evaluation device preferably also evaluates the phase position of the measurement signal and determines on the basis of the phase position, whether the error is a short circuit or an open line end.

The distance measuring device preferably comprises an impedance matching device and a coupling capacitor for coupling the feed-in signal and coupling out the reflected measuring signal from the conductor.

• 1 eine Energieübertragungsanlage, bei der an eine Freileitung ein Ausführungsbeispiel für eine erfindungsgemäße Entfernungsmesseinrichtung angeschlossen ist,
• 2 ein Ausführungsbeispiel für eine Entfernungsmesseinrichtung, die bei der Energieübertragungsanlage gemäß 1 eingesetzt werden kann, näher im Detail,
• 3-4 beispielhaft Frequenzverläufe über der Zeit zur Erläuterung der Arbeitsweise der Entfernungsmesseinrichtung gemäß 2,
• 5 ein weiteres Ausführungsbeispiel für eine Entfernungsmesseinrichtung, die für die Energieübertragungsanlage gemäß 1 geeignet ist,
• 6 ein weiteres Ausführungsbeispiel für eine Energieübertragungsanlage, bei der an eine Freileitung eine Entfernungsmesseinrichtung angeschlossen ist,
• 7 ein Ausführungsbeispiel für eine Entfernungsmesseinrichtung, bei der ausschließlich eine Fehlerüberwachung erfolgt und ggf. nur ein Fehlersignal ausgegeben wird, und
• 8 ein Ausführungsbeispiel für eine Entfernungsmesseinrichtung, bei der sowohl eine Fehlerüberwachung erfolgt und ggf. ein Fehlersignal ausgegeben sowie im Fehlerfalle außerdem der Entfernungswert, also die Fehlerentfernung, ausgegeben wird.

The invention will be explained in more detail with reference to embodiments; thereby show by way of example

• 1 an energy transmission system in which an embodiment of a distance measuring device according to the invention is connected to an overhead line,
• 2 an embodiment of a distance measuring device, which in the energy transmission system according to 1 can be used, in more detail,
• 3-4 Example frequency curves over time to explain the operation of the distance measuring device according to 2 .
• 5 a further embodiment of a distance measuring device, the energy transmission system according to 1 suitable is,
• 6 a further embodiment of an energy transmission system in which a distance measuring device is connected to an overhead line,
• 7 an embodiment of a distance measuring device in which only a fault monitoring takes place and possibly only an error signal is output, and
• 8th An exemplary embodiment of a distance measuring device, in which both an error monitoring takes place and, if necessary, an error signal is output and, in the event of an error, the distance value, ie the error distance, is also output.

For the sake of clarity, the same reference numbers are always used in the figures for identical or comparable components.

The 1 shows an energy transmission system 10 that an overhead line 20 includes. At a measuring point MST is to a leader 21 the overhead line 20 a distance measuring device 30 connected.

On the overhead line 20 An error has occurred: the conductor 21 is at a fault FS interrupted. The distance between the distance measuring device 30 or the measuring point MST and the flaw FS , so the error removal, is in the 1 with the reference number L characterized.

The 2 shows an embodiment of a distance measuring device 30 involved in the power transmission system 10 according to 1 can be used. The distance measuring device 30 according to 2 includes a signal source 31 , a receiving device 32 , an evaluation device 33 and a transmitting and receiving switch 34 ,

The signal source 31 has an analog signal generator 310 and a downstream amplifier 311 on. The amplifier 311 is the output side with the transmitting and receiving switch 34 and with the receiving device 32 connected.

The receiving device 32 includes a mixer 320 and a measuring module 321 , The mixer 320 is input side with the transmitting and receiving switch 34 and the amplifier 311 and on the output side with the measuring module 321 connected.

The distance measuring device 30 according to 2 is preferably operated as follows:

The signal generator 310 generates a frequency and / or phase modulated electrical output signal S that of the amplifier 311 amplified and as a frequency and / or phase modulated electrical feed signal e over the transmitting and receiving switch 34 in the ladder 21 the overhead line 20 according to 1 is fed. In addition, the electrical feed signal arrives e to the mixer 320 the receiving device 32 ,

The frequency and / or phase modulated electrical feed signal e gets over the ladder 21 to the fault FS transferred and from there back to the transmitting and receiving switch 34 reflected. The reflected measurement signal is in the 2 with the reference number M characterized. The reflected measurement signal M is from the transmitting and receiving switch 34 to the mixer 320 passed, which is the reflected measurement signal M with the feed signal e mixed.

The following example assumes that it is the feed signal e is a frequency-modulated feed-in signal whose frequency is ramped up over time to form a ramp function over time.

The 3 shows the course of the frequency f of the feed signal e and the frequency of the reflected measurement signal M each over time t , It can be seen that there is a difference in frequency .delta.f between the frequency f of the feed signal e and the frequency of the reflected measurement signal M gives. The frequency difference .delta.f based on the fact that the reflected measurement signal M delayed in time at the mixer 320 arrives, as it is running time - unlike the one at the mixer 320 applied electrical feed signal e - already the leader 21 to the point of failure FS and went back through. The term is expressed in the in the 3 shown frequency difference .delta.f out.

The mixer 320 generates a mixed signal on the output side MS whose frequency is the frequency difference .delta.f between the feed signal e and the reflected measurement signal M equivalent. The mixed signal MS or its frequency .delta.f is thus a measure of the running time of the feed signal e to the point of failure FS and back again and thus a measure of the distance L between the distance measuring device 30 and the flaw FS ,

The mixed signal MS is from the measurement module 321 measured, the output side, a frequency value F outputs. The frequency value F gives the frequency .delta.f the mixed signal and thus the difference frequency between the feed signal e and the reflected measurement signal M at.

wobei V die Ausbreitungsgeschwindigkeit des Messsignals auf dem Leiter, W den Entfernungswert, |Δf| den Betrag der Frequenzdifferenz zwischen der Frequenz des empfangenen Messsignals M und der aktuellen Frequenz des Einspeisesignals E zum Zeitpunkt des Eintreffens des Messsignals und df/dt die zeitliche Ableitung der Frequenz f des Einspeisesignals E nach der Zeit t bezeichnet.The frequency value F arrives at the evaluation device 33 that with the of the frequency value F specified frequency difference .delta.f one the distance L given distance value W determined, preferably as follows: $$W=\frac{V\cdot \left|\Delta f\right|}{2\cdot \left(df/dt\right)}$$

in which V the propagation velocity of the measurement signal on the conductor, W the distance value, | Δf | the amount of frequency difference between the frequency of the received measurement signal M and the current frequency of the feed signal e at the time of arrival of the measurement signal and df / dt the time derivative of the frequency f of the feed signal e after the time t designated.

In summary, the distance measuring device determines 30 the distance value W or the error removal L based on the difference frequency .delta.f and the slope df / dt of the ramp function according to 3 ,

Alternatively or additionally, the distance measuring device 30 Check if there is an error on the ladder 21 occured. For example, the distance measuring device 30 for a received reflected measurement signal M the distance to the reflection site to form the distance value W measure and this distance value W with a distance to the known conductor end of the conductor 21 indicative reference value Lmax to compare. If the distance value W smaller, in particular significantly smaller than the reference value Lmax (eg only 95% of the reference value Lmax is), it can be an error signal SF output.

The 7 shows a variant of the distance measuring device 30 , in which only an error monitoring takes place and possibly only the error signal SF is issued; the 8th shows a variant of the distance measuring device 30 , in which both an error monitoring takes place and possibly the error signal SF output as well as in the event of an error, the distance value W , So the error removal, is output.

Since the in the 3 . 7 and 8th shown increasing the frequency is technically limited upwards, the frequency response over time is preferably sawtooth or triangular. For example, the signal generator 310 switch back to a lower starting frequency after reaching an upper limit frequency, whereby a sawtooth waveform is generated, as exemplified in the 4 is shown.

In connection with the 2 to 4 and 7 to 8th became exemplary the determination of the distance value W for a frequency modulated electrical feed signal e explains; In a similar way, a distance value W on the basis of a frequency and / or phase modulated electrical feed signal e be determined by the frequency difference and / or the phase difference between the feed signal e and the reflected measurement signal M is evaluated.

The 5 shows a further embodiment of a distance measuring device that in the power transmission system 10 according to 1 can be used.

In contrast to the embodiment according to 2 the distance measuring device works 30 according to 5 without an analogue transmission and reception switch 34 ,

The distance measuring device 30 according to 5 includes a signal source 41 , a receiving device 42 and an evaluation device 43 , The signal source 41 has a digital signal generator 410 , a digital-to-analog converter 411 and an amplifier 412 on. The evaluation device 42 is through an attenuator 420 , an analog-to-digital converter 421 and a measuring module 422 educated. An output of the measuring module 422 and an output of the digital signal generator 410 each stand with the evaluation device 43 in connection.

The distance measuring device 30 according to 5 is preferably operated as follows:

The digital signal generator 410 generates on the output side a digital frequency and / or phase modulated digital output signal S that from the digital-to-analog converter 411 digitally converted to analog and subsequently from the amplifier 412 is reinforced. That from the amplifier 412 output signal forms an electrical feed signal e that in the ladder 21 the overhead line 20 according to 1 is fed.

That from the fault FS according to 1 reflected measurement signal M passes over the attenuator 420 and the analog-to-digital converter 421 to the evaluation device 43 ,

wobei V die Ausbreitungsgeschwindigkeit des Messsignals auf dem Leiter, W den Entfernungswert, |Δf| den Betrag der Frequenzdifferenz zwischen der Frequenz des Messsignals Md und der aktuellen Frequenz des Einspeisesignals E zum Zeitpunkt des Eintreffens des Messsignals Md und df/dt die zeitliche Ableitung der Frequenz f des Einspeisesignals E nach der Zeit t bezeichnet.The evaluation device 43 determines in numerical manner, for example, the frequency difference between that of the digital signal generator 410 generated output signal S and that of the measurement module 422 output digital measurement signal Md and forms the distance value W preferably according to: $$W=\frac{V\cdot \left|\Delta f\right|}{2\cdot \left(df/dt\right)}$$

in which V the propagation velocity of the measurement signal on the conductor, W the distance value, | Δf | the amount of frequency difference between the frequency of the measurement signal Md and the current frequency of the feed signal e at the time of arrival of the measurement signal Md and df / dt the time derivative of the frequency f of the feed signal e after the time t designated.

The digital signal generator 410 , the evaluation device 43 and the measurement module 422 can through a digital signal processor DSP be formed.

Also, in the distance measuring device 30 according to the 5 - Alternatively or additionally - a fault detection be provided as such, as above in connection with the 7 and 8th has been explained; In this regard, reference should be made to the above statements in connection with 7 and 8th directed.

The 6 shows an alternative embodiment for the power transmission system 10 according to 1 in which the distance measuring device 30 not directly to the ladder 21 connected but via a coaxial cable 60 , an impedance matching device 70 and a coupling capacitor 80 , Incidentally, the above explanations apply in connection with 1 to 5 and 7 to 8th corresponding.

In connection with the 1 to 8th were exemplary embodiments for determining an error distance using the example of a single conductor 21 explains; Correspondingly, error margins on other conductors of the energy transmission system 30 be determined.

The in connection with the 1 to 8th exemplified embodiments can be advantageously combined with powerline systems. It is also possible to determine whether a switch or disconnector on the line is open or closed, as an open switch / disconnector as well as a disconnected line reflects the feed signal.

The in connection with the 1 to 8th Exemplary embodiments explained can be used advantageously for monitoring HVDC lines and cables, in particular for monitoring in normal operating state de-energized DMR conductors (Dedicated Metalic Return) and ground lines (line from the HVDC station to the ground point). It is advantageous to monitor the operational readiness of the DMR conductor, as it may be necessary to switch over to this conductor if there is a fault in the HVDC system.

While the invention has been further illustrated and described in detail by way of preferred embodiments, the invention is not limited by the disclosed examples, and other variations can be derived therefrom by those skilled in the art without departing from the scope of the invention.

LIST OF REFERENCE NUMBERS

10

Power transmission system

20

overhead line

21

ladder

30

Distance measuring device

31

source

32

receiver

33

evaluation

34

Transmitter and receiver switch

41

source

42

receiver

43

evaluation

60

coaxial

70

Impedance matching device

80

coupling capacitor

310

signal generator

311

amplifier

320

mixer

321

measurement module

410

signal generator

411

Digital to analog converter

412

amplifier

420

attenuator

421

Analog to digital converter

422

measurement module

DSP

digital signal processor

e

feed signal

f

frequency

F

frequency value

FS

fault location

L

Error removal / distance

Lmax

reference value

M

measuring signal

Md

digital measuring signal

MS

mixed signal

MST

measuring point

S

output

SF

error signal

t

Time

W

Distance value

.delta.f

Frequency difference

Claims (21)

Method for determining the distance (L) of a reflection point on an electrical conductor (21), characterized in that - a frequency- and / or phase-modulated electrical feed-in signal (E) is generated, - the feed-in signal (E) at a measuring point (MST) in the conductor (21) is fed, - a signal to the measuring point (MST) reflected, hereinafter referred to as measuring signal (M), at the measuring point (MST) is measured and - based on the frequency (f) and / or phase of the measuring signal (M ) and based on the current frequency (f) and / or phase of the feed signal (E) at the time of arrival of the measurement signal (M), a distance value (W) indicating the distance of the reflection point is determined. Method according to Claim 1 , characterized in that - the distance value (W) is compared with a reference value (Lmax) indicating the distance to the known conductor end of the conductor (21) and - an error signal (SF) is generated if the distance value (W) is less than the reference value (Lmax) is. Method according to Claim 2 , characterized in that in the presence of the error signal (SF) of the distance value (W) is output as the error removal value. Method according to one of the preceding claims, characterized in that after an error has been detected on the conductor by means of an external error detection method and a external error signal is present, the distance value (W) is determined and this is output as the error removal value. Method according to one of the preceding claims, characterized in that - a frequency-modulated signal is generated as feed signal (E) by changing the frequency (f) of the feed signal (E) over time in accordance with a predetermined change function, - the frequency (f) the measurement signal (M) reflected from the reflection point to the measuring point (MST) is measured, and - based on the frequency (f) of the received measurement signal (M) and on the current frequency (f) of the feed signal (E) at the time of the arrival of the measurement signal ( M) of the distance of the reflection point indicating distance value (W) is determined. Method according to Claim 5 , characterized in that - the change function is a ramp function or sawtooth function and - is formed as the frequency-modulated feed signal (E) an injection signal (E) with a ramped or sawtooth-shaped frequency response. Method according to one of the preceding claims, characterized in that the feed-in signal (E) is fed into a currentless in the error-free operating state return conductor of a high-voltage direct-current transmission line. Method according to one of the preceding claims, characterized in that as the feed signal (E) a frequency-modulated signal of constant amplitude in the conductor (21) is fed. Method according to one of the preceding claims, characterized in that the frequency (f) of the feed signal (E) is changed in a range between 1 kHz and 1 MHz, wherein the temporal change of the frequency (f) or the derivative of the frequency (f ) is constant over time. Method according to one of the preceding claims, characterized in that the distance value (W) is determined according to $$W=\frac{V\cdot \left|\Delta f\right|}{2\cdot \left(df/dt\right)}$$

where V is the propagation velocity of the measurement signal on the conductor, W is the distance value, | Δf | the amount of the frequency difference between the frequency (f) of the received measurement signal (M) and the actual frequency (f) of the feed signal (E) at the time of arrival of the measurement signal (M) and df / dt the time derivative of the frequency (f) of the Infeed signal (E) referred to the time. Method according to one of the preceding claims, characterized in that - the frequency (f) of the feed signal (E) in a range between 30 kHz - 500 kHz is increased or decreased within a period of 1 s and / or - the feed signal (E) with a power between 50 W and 150 W in the conductor (21) is fed. Method according to one of the preceding claims, characterized in that the reflected measuring signal (M) and the feed signal (E) are mixed in a mixer (320) and the distance value (W) is determined on the basis of the frequency (f) of the mixing signal (MS) , Method according to one of the preceding claims, characterized in that - the feed signal (E) via a transmitting and receiving switch (34) is fed into the line and - the reflected measuring signal (M) via the transmitting and receiving switch (34) is received , Method according to one of the preceding claims, characterized in that - the feed-in signal (E) with a digital output signal (S) of a digital signal generator (410), a signal generator (410) downstream digital-to-analog converter (411) and the digital Analog converter (411) downstream amplifier (412) is generated, - the reflected measurement signal (M) is fed to an analog-to-digital converter (421) and, - with the output signal of the analog-to-digital converter (421) and the digital signal generator ( 410) generated digital output signal (S) of the distance value (W) is determined. Method according to Claim 14 , characterized in that - the reflected measurement signal (M) by means of an attenuator (420) is first attenuated and - the attenuated signal in the analog-to-digital converter (421) is fed. Method according to one of the preceding claims, characterized in that the electrical conductor (21) is a conductor (21) of an overhead line or a cable for power transmission. Distance measuring device (30) for determining the distance (L) of a reflection point, in particular an error, on an electrical conductor (21), characterized a signal source (31, 41) for generating a frequency- and / or phase-modulated electrical feed-in signal (E), - a receiving device (32, 42) for measuring a measurement signal (M) reflected from the reflection point to the measuring point (MST) and - an evaluation device (33, 43), based on the frequency (f) and / or phase of the measurement signal (M) and based on the current frequency (f) and / or phase of the feed signal (E) at the time of arrival of the measurement signal (M) one Distance of the reflection point indicating distance value (W) determined. Distance measuring device (30) after Claim 17 characterized in that - the signal source (31, 41) is arranged to generate a frequency modulated feed signal (E) as the feed signal (E) by adjusting the frequency (f) of the feed signal (E) over time in accordance with a changes the predetermined change function, and - the evaluation device (33, 43) is designed such that it based on the frequency (f) of the measurement signal (M) and the current frequency (f) of the feed signal (E) at the time of arrival of the measurement signal ( M) determines the distance value (W). Distance measuring device (30) after Claim 17 or 18 , characterized in that the distance measuring device (30) can transmit and receive simultaneously, ie the signal source (31, 41) can feed the feed signal (E), while the receiving device (32, 42) receives the measuring signal (M) and the evaluation device ( 33, 43). Distance measuring device (30) according to one of the preceding Claims 17 to 19 , characterized in that the evaluation device (33, 43) evaluates the phase position of the measuring signal (M) and determines on the basis of the phase position, if the fault is a short circuit or an open line end. Distance measuring device (30) according to one of the preceding Claims 17 to 20 , characterized in that the distance measuring device has an impedance matching device (70) and a coupling capacitor (80) for coupling the feed-in signal (E) and decoupling the reflected measurement signal (M) from the conductor.

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