EP3857242A1

EP3857242A1 - Method and measuring assembly for detecting faults on electrical lines

Info

Publication number: EP3857242A1
Application number: EP19801486.2A
Authority: EP
Inventors: Robert Baumgartner; Claus Seisenberger
Original assignee: Siemens AG
Current assignee: Siemens AG
Priority date: 2018-11-21
Filing date: 2019-10-21
Publication date: 2021-08-04
Also published as: US20220011359A1; BR112021009736A2; WO2020104124A1; US11867742B2; DE102018219959A1

Abstract

The present invention relates to a method for detecting faults on an electrical line (6), in which a measurement signal is fed to a first location (11) on the line (6) by means of a measuring assembly (7, 8, 9, 10), and a reflected measurement signal is received at the first location (11), and a fault location on the line (6) is determined on the basis of the period of time until the reflected measurement signal is received and by considering a line attenuation, characterised in that a reflection location (12) on the line (6) where the measurement signal is reflected is used, and the line attenuation is determined on the basis of the level of the reflected measurement signal received at the first location (11). The invention further relates to a corresponding measuring assembly.

Description

description

Method and measuring arrangement for fault detection on electrical lines

The invention relates to a method for fault detection on electrical lines according to the preamble of claim 1 and a measuring arrangement according to the preamble of claim 11.

In the case of overhead lines and underground cables for energy transmission, malfunctions occasionally occur, for example because the line is torn off, an underground cable is cut or a line short-circuit or an earth fault is present. This can lead to a relatively long power interruption, especially with very long lines, if it is not known at which point the error occurred.

In addition to the current-carrying lines, in which a fault can be recognized at least immediately, currentless lines are also of interest, for example the dedicated return conductor for HVDC lines (HVDC: high-voltage direct current

transmission), which normally carries no voltage.

Reflectometry methods are often used for fault detection and fault localization on high-voltage overhead lines. A device for sending and receiving measurement signals is coupled to the line at the beginning of the line. This device generates e.g. periodically a measuring pulse that is injected into the line. This pulse signal propagates along the overhead line. If a line fault occurs on a line, this causes a jump in the line impedance at the fault location. An earth fault causes an impedance close to zero, while an open circuit causes a high-resistance fault.

A measuring signal that meets the impedance jump at the fault location is partially or completely reflected at this point. animals. The reflected signal runs back to the measuring device. There the signal can be detected and the position of the error can be determined from the running time.

Due to the line attenuation, reflections from more distant fault locations have a lower level than nearby fault locations. If a fixed threshold value for the signal level of an error is used for error detection, removed errors cannot be detected or can only be detected with lower sensitivity. Therefore, e.g. a compensation factor is set when installing the device, which increases the signal level depending on the runtime. The line attenuation is consequently once determined and permanently set during installation. A fixed threshold for the detection of errors is derived.

From the previously unpublished German patent application 102017214996.5 of August 28, 2017, a method for determining the distance of a reflection point on an electrical conductor is known, in which a frequency and / or phase modulated electrical feed signal is generated. The feed signal is fed into the conductor at a measuring point. A signal or measuring signal reflected to the measuring point is measured at the measuring point. On the basis of the frequency and / or phase of the measurement signal and on the basis of the current frequency and / or phase of the feed signal at the time of arrival of the measurement signal, a distance value indicating the distance of the reflection point is determined.

Based on known methods for fault detection on egg ner electrical line, the object of the invention is to provide a method with which a comparatively accurate determination of a fault location can be achieved, in particular with long electrical lines.

The invention solves this problem by a method according to claim 1. The first location is, for example, a first line end or another point along the line at which the measuring arrangement is connected.

The fault location is the location of a fault on the line. The fault location is often located between the first location and the reflection location. However, the fault location can also be behind the reflection location, viewed from the first location, because the reflection location does not have to cause total reflection of the measurement signal.

A reflection location is a location along the line, e.g. a second conductor end with a galvanic connection to a downstream electrical device. An open conductor end, i.e. a cable end without such a galvanic connection, can also be a place of reflection.

The method according to the invention takes into account that a line loss of e.g. Overhead lines do not remain constant during operation, but change due to environmental influences (e.g. the ambient temperature. The actual line attenuation can therefore deviate from the set line attenuation, which in previous methods results in a different sensitivity of error detection over the line length. Especially with very long lines For example, with a length of more than 100 km, the line attenuation - caused by the temperature change within one day - can fluctuate by several dB.

The main idea of the present method is to use a reflection, such as an end reflection at a second line end of a high-voltage overhead line, to determine a current line loss and thus to readjust a detection threshold for errors. For example, this readjustment can take place continuously, that is to say with a short time cycle of, for example, a few minutes. It is an advantage of the method according to the invention that the detection sensitivity for errors is constant over the entire line length. The detection sensitivity remains constant even with changes in the line attenuation. Furthermore, the detection threshold can be set more sensitively since there are no sensitivity fluctuations over the line length. This also makes it possible to detect high-resistance faults.

Furthermore, slowly occurring errors can be detected, e.g. when a tree grows in the direction of the high-voltage line. With previous systems, however, a high-pass filter is often used in the detection in order to slow down

Eliminate fluctuations.

The damping fluctuations are considerable, in particular in the case of very long lines, so that the sensitivity in the distant region can be significantly stabilized with the method according to the invention.

In a preferred embodiment of the method according to the invention, the fault location is transmitted to a control center and used to trigger a shutdown of the line or an affected line section. Furthermore, the control center can initiate maintenance or repair at the fault location.

In a further preferred embodiment of the method according to the invention, an impedance device is used at the reflection site.

In a further preferred embodiment of the method according to the invention, a choke coil is used for the impedance device. This is an advantage because a choke coil causes a strong impedance jump at the end of the line, which causes an end reflection and thus makes the measurement method according to the invention possible. In a further preferred embodiment of the method according to the invention, the inductor is used as part of a powerline communication device. On lines with PLC (Power Line Communication), a choke is typically connected in series on both lines to prevent the propagation of the communication signals transmitted via the power line beyond the end of the line. Such a choke forms a high-impedance impedance at signal frequencies in the kHz range.

In a further preferred embodiment of the method according to the invention, a short circuit between the line and earth is used for the impedance device.

In a further preferred embodiment of the method according to the invention, a measurement signal in the kHz frequency range is used. A kHz frequency range includes, for example, frequencies between 1 kHz and 1000 kHz. This is an advantage because such a measurement signal can be reflected in particular by a choke.

In a further preferred embodiment of the method according to the invention, a measurement signal with a frequency in the frequency range from 50 kHz to 5 MHz is used. This is an advantage because it has been shown that this frequency range is particularly well suited for a reflection measurement. This applies particularly to long lines with a length of more than 100 km.

In a further preferred embodiment of the method according to the invention, a line with a length of more than 100 km is used for the electrical line.

In a further preferred embodiment of the method according to the invention, the line attenuation is compensated by normalizing the level of the measurement signal reflected from the reflection location to zero decibels and linearly increasing the level of the reflected measurement signal along the line length. will. This is an advantage because the detection sensitivity to errors remains constant over the entire length of the line. This approach is based on the assumption that the reflection usually corresponds approximately to a total reflection and the line attenuation increases proportionally with the line length.

In a further preferred embodiment of the method according to the invention, a first threshold value for the level of the normalized reflected measurement signal is defined, an error on the line being detected when the first threshold value is exceeded. For example, a first threshold of -10 dB can be set. However, another suitable threshold value can be determined from empirical values from series tests, which on the one hand makes errors reliably recognizable and on the other hand minimizes the risk of false alarms.

In a further preferred embodiment of the method according to the invention, the compensation of the line loss is adjusted at a regular time interval in order to compensate for a change in the line loss due to a temperature change in the environment of the line. For example, the line loss can be adjusted every 10 seconds, every hour or several times a day. The more often a readjustment takes place or the reflection measurement is repeated, the more precisely the line loss is compensated for and the more reliable the error detection.

In a further preferred development of the aforementioned embodiment of the method according to the invention, the compensation of the line loss is adapted for each error-free measurement. This means that when the method for error detection on the line is carried out according to the invention, the line attenuation is tracked in order to achieve a constant sensitivity to errors, for example during the course of the day. In a further preferred embodiment of the method according to the invention, the reflection location is determined on the basis of a period of time until reception of the reflected measurement signal and taking into account line attenuation. This is an advantage because temperature-related changes in the line length can also be determined.

In a further preferred embodiment of the method according to the invention, a second threshold value is set for the level of the normalized reflected measurement signal, an error in the measurement arrangement and / or a line attenuation being below the second threshold value such that a reliable fault location cannot be determined , be recognized. For example, a second threshold of -80 dB can be set. However, it is also possible to determine another suitable threshold value based on empirical values from series tests, which on the one hand reliably detects device faults and on the other hand minimizes the risk of undetected faults on the line.

In a further preferred embodiment of the method according to the invention, a line which is in the fault-free operating state and is de-energized in a high-voltage direct current transmission line is used as the line. The method according to the invention can also advantageously be used for earth electrode lines at HVDC stations.

In a further preferred embodiment of the method according to the invention, an overhead line is used as the line. This is an advantage because precise fault detection and fault location determination are important, especially with long overhead lines.

In a further preferred embodiment of the method according to the invention, a pulse method is used for the measurement signal. In a further preferred embodiment of the method according to the invention, a frequency-modulated continuous wave (FMCW) method is used for the measurement signal. A continuous measurement signal is fed in, the operating frequency of which is changed. FMCW methods are known for example as frequency-modulated continuous wave radar.

In a further preferred embodiment of the method according to the invention, alternatively and / or in addition to an end reflection at the second end of the line, another reflection point within the line course is used to determine the line loss.

Starting from known measuring arrangements for fault detection on an electrical line, the object of the invention is to provide a measuring arrangement with which a comparatively precise determination of a fault location can be achieved, in particular in the case of long electrical lines.

The invention solves this problem by a measuring arrangement according to claim 11.

A signal transmitter device is, for example, a device that is suitable for generating a measurement signal in the kHz range. A receiving device in turn is suitable for collecting the reflected measurement signal and, if necessary, amplifying it for further evaluation. For this purpose, the signaling device and the receiving device can be positioned at the same location.

An evaluation device is, for example, a computer or a computer with a data memory, the evaluation being carried out by software provided for this purpose. The evaluation device can be provided together with the signaling device and the receiving device at the same location or also centrally, for example as a cloud application on a remote data center. Preferred embodiments of the measuring arrangement according to the invention result from claims 12 to 15.

In a further preferred embodiment of the measurement arrangement according to the invention, the reflection location has an impedance device which is suitable for reflecting the measurement signal. For example, the reflection location is a second line end.

In a further preferred embodiment of the measuring arrangement according to the invention, the impedance device has a choke coil. This is an advantage because a choke coil causes a strong impedance jump at the line end, which causes an end reflection and thus makes the measurement method according to the invention possible.

In a further preferred embodiment of the measuring arrangement according to the invention, the inductor is provided as part of a powerline communication device. On lines with PLC (Power Line Communication), a choke is typically connected in series on both lines to prevent the communication signals transmitted via the power line from spreading beyond the end of the line. Such a choke forms a high-impedance impedance at signal frequencies in the kHz range.

In a further preferred embodiment of the measuring arrangement according to the invention, a short circuit between the line and earth is used for the impedance device.

Further variants of the method according to the invention, as described at the beginning, can easily be implemented by means of the measuring arrangement according to the invention.

This results in the same advantages for the measuring arrangement and its execution forms as explained at the beginning for the method according to the invention. For a better explanation of the invention show the schematic representation

Figure 1 shows a first reflection diagram of an electrical

Line, and

Figure 2 shows a second reflection diagram of an electrical

Line with line loss compensation, and

Figure 3 shows a third reflection diagram of an electrical

Line with compensation of the line loss and a first threshold for error detection, and

Figure 4 shows a fourth reflection diagram of an electrical

Line with modified line loss, and

Figure 5 shows a measuring arrangement.

FIG. 1 shows a first reflection diagram of an electrical line. The length of the line in km is plotted on the horizontal axis. On the vertical axis A, the level or the maximum amplitude of a reflected measurement signal 1 received at the first end of the line - at zero km - is plotted in decibels. By definition, a received signal level of zero decibels corresponds to the fed-in signal level of the original measurement signal. In the example shown, the line is 190 km long, so that there is a high level for an end reflection 2 at the second end of the line at 190 km line length L. As can be seen, the level of the reflected signal continues to decrease with increasing cable length.

FIG. 2 shows a second reflection diagram of an electrical line with compensation for the line loss. The level of the reflection at the end of the line - the end reflection - is used to continuously determine the line loss and to adjust the detection threshold accordingly. After each reflection measurement, such as in FIG. 1, the level of the final reflection 2 is determined. With the assumption that the end reflection 2 usually corresponds to a total reflection and the line loss increases proportionally with the line length, the line loss can be compensated for. For this purpose, the level of the reflection signal 4 is raised linearly with the line length, in such a way that the level of the end reflection 3 in FIG. 2 is OdB.

FIG. 3 shows that a first threshold value as a detection threshold for line faults can be placed as a horizontal line 5 with a defined distance below the zero line (zero dB). A constant error sensitivity is thus achieved over the entire length of the line, which is a major advantage of the method according to the invention.

This method is used, for example, both in the first measurement after installation and in subsequent operation in order to continuously determine the line loss and to compensate for the next measurement.

FIG. 4 shows a measurement in which the actual line loss deviates from the previously compensated line loss and should be readjusted in the next measurement. The level of the final reflection is a few dB above the zero line. After readjustment, the reflection diagram should again correspond to FIG. 2.

A typical frequency range for a reflection measurement with a measurement signal on high-voltage lines is between 30 kHz and 5 MHz.

FIG. 5 shows a measuring arrangement 7, 8, 9, 10 for error detection on an electrical line 6, having a signaling device 7, which is arranged and formed at a first end 11 of line 6, a measurement signal in the first end 11 of line 6 feed. A receiving device 8, which is arranged at the first end 11 of the line 6, is designed to receive the reflected measurement signal.

An evaluation device 9 is designed to determine an error location 13 on line 6 on the basis of the time period until the reflected measurement signal is received and taking into account line attenuation.

The signaling device 7 and the receiving device 8 are integrated together with the evaluation device 9 in a first communication device 15 for powerline communication via the line 6. The first communication device 15 has a throttle 16. An impedance device 10, which is designed as a choke 10 and is integrated in a second communication device 14 for powerline communication via the line 6, is arranged on the second line end 12. The choke 10 is suitable for reflecting the measurement signal.

Furthermore, the receiving device 8 is designed to receive the final reflection of the measurement signal from the second line end 12. The evaluation device 9 is designed as a conventional computer and can determine the line loss on the basis of the level of the end reflection.

Claims

1. A method for fault detection on an electrical line (6), in which a measurement signal is fed to a first location (11) on the line (6) by means of a measuring arrangement (7, 8, 9, 10), and

a reflected measurement signal is received at the first location (11), and

a fault location on the line (6) is determined on the basis of the time until the reflected measurement signal is received and taking line attenuation into account,

characterized in that

a reflection location (12) on the line (6) is used, at which the measurement signal is reflected, and that

the line loss is determined on the basis of the level of the reflected signal received at the first location (11).

2. The method according to claim 1, characterized in that an impedance device (10) is used at the reflection location (12).

3. The method according to claim 2, characterized in that a choke coil (10) is used for the impedance device.

4. The method according to any one of the preceding claims, characterized in that a measurement signal is used in the kHz frequency range.

5. The method according to any one of the preceding claims, characterized in that a measurement signal with a frequency in the frequency range from 50 kHz to 5 MHz is used.

6. The method according to any one of the preceding claims, characterized in that the line loss is compensated by normalizing the level of the measurement signal reflected from the reflection location to zero decibels and the level of the reflective is measured linearly along the cable length.

7. The method according to claim 6, characterized in that a first threshold value (5) is set for the level of the normalized reflected measurement signal (4), an error on the line being detected when the first threshold value (5) is exceeded.

8. The method according to claim 6 or 7, characterized in that the compensation of the line loss is adjusted with a regular timing to compensate for a change in line loss due to a temperature change in the environment of the line (6).

9. The method according to any one of the preceding claims, characterized in that the reflection location (12) is determined on the basis of a period of time until the reception of the reflected measurement signal and taking into account line attenuation.

10. The method according to any one of the preceding claims, characterized in that a second threshold value is set for the level of the normalized reflected measurement signal (4), wherein when the second threshold value (4) is undershot, an error in the measuring arrangement (7,8,9 , 10) and / or a line attenuation so great that no reliable location of the fault is possible.

11. Measuring arrangement (7,8,9,10) for error detection on an electrical line (6), having one

Signaling device (7), which is arranged and configured at a first location (11) on the line (6), to feed a measurement signal into the line (6), and

a receiving device (8), which is arranged at the first location (11) and designed to receive a reflected measurement signal, and

an evaluation device (9) which is designed on the basis of the time period until the reflected measurement signal is received and taking into account a line loss

Determine the fault location (13) on the line (6),

characterized in that

a reflection location (12) is arranged on the line (6), at which the measurement signal is reflected, and that

the receiving device (8) is designed to receive the reflected measurement signal from the reflection location (12),

and that

the evaluation device (9) is designed to determine the line attenuation on the basis of the level of the reflected measurement signal received at the first location (11).

12. Measuring arrangement (7, 8, 9, 10) according to claim 11, characterized in that the evaluation device (9) is designed to compensate for the line attenuation by normalizing the level of the measurement signal reflected from the reflection location to zero decibel and the level of the reflected measurement signal is linearly increased along the line length.

13. Measuring arrangement (7, 8, 9, 10) according to claim 11 or 12, characterized in that the evaluation device (9) is designed to set a first threshold value for the level of the normalized reflected measurement signal, an error when the first threshold value is exceeded is recognized on the line (6).

14. Measuring arrangement (7, 8, 9, 10) according to claim 12 or 13, characterized in that the evaluation device (9) is designed to adapt the compensation of the line attenuation with a regular clock cycle in order to change the line attenuation as a result of a temperature change in the reverse direction Exercise the line (6) to compensate.

15. Measuring arrangement (7, 8, 9, 10) according to one of claims 11 to 14, characterized in that the evaluation device (9) is designed, based on a period of time until the reception of the reflected measurement signal and taking into account a line attenuation, the reflection location determine.