WO2004046702A1

WO2004046702A1 - Method and device for determining properties of soil by means of transmission properties of an overhead line, e.g. an overhead electric cable

Info

Publication number: WO2004046702A1
Application number: PCT/EP2003/011975
Authority: WO
Inventors: Alexander Brandelik; Christof HÜBNER
Original assignee: Forschungszentrum Karlsruhe Gmbh
Priority date: 2002-11-19
Filing date: 2003-10-29
Publication date: 2004-06-03
Also published as: AU2003283312A1; EP1565730A1; DE10253772A1; DE10253772B4

Abstract

The invention relates to a method for determining properties of soil, especially the humidity content thereof. Said method comprises the following steps: a temporary or permanent electromagnetic field is generated in at least one electroconductive overhead line by applying an alternating voltage, in such a way that the at least one field penetrates the soil; at least the running time of the wave packet used to generate the temporary electromagnetic field, or a change in the alternating voltage parameters of the field between at least two points interspaced in the longitudinal direction of the overhead line, is measured; and the at least measured running time and/or the measured change in the alternating voltage parameters between the at least two points in the at least one electroconductive overhead line are compared with standard values.

Description

METHOD AND DEVICE FOR DETERMINING PROPERTIES OF THE GROUND ON THE BASIS OF THE TRANSMISSION PROPERTIES OF AN ABOVE-LEADED LINE, e.g.

A CURRENT POWER LINE

The invention relates to a method and a device for determining 5 properties of the soil, in particular the moisture content, and of heights of snow and ice cover.

The precise and large-scale determination of properties of the soil, in particular moisture content, is important for estimating and managing water resources, for example for agriculture and forestry. Only with this knowledge, for example, can irrigation and harvest forecast be adapted on a large scale.

15 The properties of the soil, particularly its moisture content, also play an important role in public building projects, for example road construction, where the subsurface must not be too moist.

The increasing amount of water vapor, which depends on the soil moisture, also plays a significant role in the meteorological forecast.

In the present invention, moisture is to be understood to mean any type of water. So in addition to water, 25 moisture and snow also fall under moisture, possibly also as a covering of the ground.

The determination of the amount of snow and ice is important for the avalanche forecast and for warning of flooding during the spring melt and for the prediction of the level of water reservoirs filled with 30 meltwater. A moisture sensor for extended layers is known from WO 96/22522, which in each case consists of at least one high-frequency electrical signal generator, a signal propagation time measuring device, a reflectometer and a line system composed of at least two independent lines which do not touch and cross each other. However, this moisture sensor is disadvantageous because it has to be introduced into the ground for operation, which is expensive, complex and mechanically complicated, especially when it comes to snow fields. Furthermore, the length of the sensor, ie the area examined, is limited and has only a limited measuring range around the jvless line, since the spread of the measuring field into the ground or snow field is small due to the small line diameter.

The object of the present invention is to provide a method and a device with which it is possible to carry out the determination of properties of the soil, in particular moisture content or snow or ice thicknesses, over a wide area without great technical effort.

This task is solved by a method which comprises the steps

Generation of a time-limited or permanent electromagnetic field in at least one electrically conductive above-ground line by applying an alternating voltage such that the at least one field extends into the ground,

Measurement of at least the running time of the one used to generate the time-limited electromagnetic field

Wave packet or a change in the AC voltage parameters of the field between at least two points spaced apart in the longitudinal direction of the line in the at least one above-ground line,

Comparison of the at least measured transit time and / or the measured change in the AC voltage parameters between the at least two points in the at least one electrically conductive above-ground line with standard values.

includes.

The object is also achieved by a device for coupling to at least one electrically conductive above-ground line

at least one generator for generating a time-limited or permanent AC voltage

Connection to the at least one electrically conductive above-ground line,

at least one receiver for connection to the at least one electrically conductive above-ground line and spaced in the longitudinal direction of the line from the at least one generator, and

at least one measuring device for recording the transit time of the wave packet used to generate the time-limited electromagnetic field and / or changing at least one parameter of the AC voltage

solved. Due to the use of an electrically conductive above-ground line to generate the electromagnetic field that extends into the ground, it is possible to measure a large area due to the distance to the ground. The difficult installation of the line in the ground or a snow field is also eliminated.

According to the invention, in principle any type of overhead lines already installed, i.e. H. Cables that are installed above ground at a certain distance from the ground are used.

It is particularly preferred if the electrically conductive above-ground line comprises one or more lines selected from the group consisting of overhead power lines, supply lines, above-ground telephone lines, overhead rail lines, cable car lines.

Such lines already exist and therefore no new complex construction measures have to be taken and the area covered by such lines practically covers the entire globe, so that the measuring range under these lines is enormous. A similarly large surface is covered as would otherwise only be possible with satellite or airborne measurement technology. In particular, the measuring method is independent of the soil from the soil, for example, from its growth and / or local nature (rock, rivers, lakes, etc.) due to the spacing of the measuring line.

For reasons of economy, such lines are spanned so low above the ground that a well-measurable proportion of the electromagnetic field generated by the measuring line extends into the ground below. The properties of the soil or soil coverings to be determined (e.g. vegetation or snow) influence the electrical properties of the soil or its cover, which is penetrated by the electromagnetic field, such as conductivity, dielectric properties (dielectric constant) and magnetic permeability. This in turn affects the spread of the field along the line.

In most soils and coverings, where there is only negligible or no magnetization, the field is

(Measurement signal) only influenced by the first two properties.

The conductivity and the dielectric in a complex manner cause both an attenuation and a time delay of the field.

The conductivity and dielectric of the soil or its coverings also depend on their moisture content.

It is thus possible to determine the nature of the soil by measuring the deceleration and / or the damping by determining the conductivity and the dielectric constant. It was already known to the person skilled in the art that the signal transmission is influenced by the soil properties. These effects, which were previously considered disruptive, have now surprisingly been recognized as the primary parameters for determining the nature of the soil.

It was surprising and unpredictable for the person skilled in the art that the dielectric constant and the conductivity and thus the moisture content of the soil can be calculated by measuring the signal delay and / or attenuation.

The assignment of the moisture content to the conductivity and the dielectric can be done by calibration, for which these parameters and the moisture of a soil sample is measured at different moisture levels (for example after oven drying) to determine calibrated standard values. During the actual later measurements, of course, the other sizes (such as growth and vegetation stage) must correspond to those of the calibrated samples, so that the calibrated standard values are suitable for comparison.

The actual assignment can be carried out, for example, with sufficient accuracy by three-dimensional electromagnetic field calculations (analytical or numerical) known to the person skilled in the art, which use the dielectric constant and the conductivity. For these calculations, the dielectric constant and conductivity of the soil with different water content are required. Sufficiently accurate, approximate values are known to the person skilled in the art and can, for. B. from the book "Dielectric Properties of Heterogeneous Materials", Editor A. Priou, PIER 6 Progress in Electromagnetics Research, 1992 Elsevier Science Publishing Co. New York.

In the field of determining the moisture content of the soil (including snow), many recommendations for calculating the dielectric constant and the conductivity of the soil have been developed by Birchak et al. recommended mathematical functions (mixing rules) very well proven ("High dielectric constant microwave probes for sensing soil moisture", Proceedings of the IEEE, 62 (1), 93 - 98, 1974).

Because the inclusion of a full set of standard values

(Calibration curve) requires a large number of measurements, it is possible to combine the values of the calibration with those of the field calculation, so that only a few measured values are required to set up the calibration curve. In In this case, the relative course of the calibration curve is recorded using the mathematical functions (mixing rules) specified above. This relative calibration curve is then itself calibrated using _ at least one absolute value that comes from a sample measurement, that is to say adapted to the absolute value. Several absolute values for calibration provide higher accuracy.

The electrically conductive above-ground lines preferably comprise individual lines and / or two-wire and / or multi-wire. For example, the high-voltage overhead lines for power transmission are three or more lines installed on masts. Examples of two-wire are low-voltage supply lines for small consumers, as they are widely installed above the streets in small communities. Telephone lines are also often designed as two-wire. Railway overhead lines and cable car lines are mostly single lines.

The at least one electrically conductive above-ground line can be shut down during the measurement for your normal operation, i. H. it is only used as a measuring line. This can either be a dedicated measuring line or the line is shut down for the short time of the measurement (maximum a few seconds), for example for the power supply or for making calls.

On the other hand, it is possible that the at least one electrically conductive above-ground line remains available for your normal operation during the measurement.

It then makes sense that the measurement signal by means of frequency-selective coupling elements and / or high-frequency blocks (RF blocks), such as. B. Transformers, coupling capacitors, filters or crossovers are added to the primary transmission variable, ie are modulated on. Then the measurement signals do not impair the primary functions of the line system.

It is therefore preferred if the generator and / or the measuring device are connected to the at least one electrically conductive above-ground line via coupling elements and, if appropriate, high-frequency blocks are arranged in front of and behind a measuring section on the at least one electrically conductive above-ground line.

A corresponding technique has been developed for use on high-voltage overhead lines for call and

Service circuit transmissions developed and used in the 1960s (carrier frequency message transmission via

High-voltage power lines, Siemens magazine issue 8, August 1965, pages 898 to 904; Carrier frequency equipment in high voltage AC networks and on DC transmission lines, Brown Boveri Mitteilungen, Volume 53, No. 4/5, April / May 1966, pages 350 to 364). With the technical development of wireless telephony and satellite technology, this so-called "carrier frequency message transmission via high-voltage lines" became obsolete and therefore switched off and dismantled. The methods and devices used at that time can - if necessary with changes - be used to carry out the method according to the invention.

Basically, measurements with the above-mentioned goal are possible both in the time domain and in the frequency domain. For moisture content measurements in soils, a frequency range between 1 and 1000 MHz is favorable, the higher the frequency, the smaller the damping caused by the soil, but also the possible Penetration depth of the measuring field. This must be taken into account when selecting the frequency range. In traditional soil moisture measurement technology, a frequency range between 100 and 1000 MHz is used, in that the attenuation becomes negligible and the moisture only correlates with the dielectric. This simplifies the calculation ("Subsurface Sensing and Subsurface Aquametry", Subsurface Sensing Technologies and Applications, An International Journal, Volume 1, Number 4, October 2000, Kluwer Academic / Plenum Publishers; "RF & Microwave Sensing of Moist Materials, Food and other Dielectrics ", Sensor Update Volume 7, Wiley-VCH Weinheim 2000). If high-frequency transmission is not possible because, for example, the distance between the individual lines is very large, as is often the case with overland lines, you can also work in lower frequency ranges.

It is known from the prior art that a frequency range of approximately 30 to 450 kHz is suitable for the economical transmission of messages on high-voltage lines ("Telecontrol transmission on high-voltage lines", Siemens-Zeitschrift, July 1957, No. 7). These frequency ranges can also be used for the method according to the invention. However, due to technical improvements, even lower frequencies than the 30 kHz limit at that time can be used.

Thus, according to the invention, a frequency range between 1 kHz and 450 kHz and / or 1 to 1000 MHz can be used for the measurement.

However, the damping in the low frequency range is no longer negligible. Therefore, conductivity will also be an essential parameter in the link between the electrical properties of the soil and the moisture content. In this case two-dimensional standard values are used. It should be taken into account that the possibility of measuring in the time domain at these low frequencies is severely restricted.

However, time-limited, low-frequency signal packets can then be used, which are suitable for measuring the throughput time along a long line. Such signal packets are common and known to the person skilled in the art. However, the signal waveform will be greatly deformed at the end and beginning of the packet, i.e. H. wear out, making it difficult to measure time.

In the frequency domain measurement method, the above-mentioned delay (due to the wet floors) can be replaced by measuring the phase change of the signal. The wetter the soil, the greater its dielectric constant and thus the phase change along the line. If the line is so long that several wavelengths of the measurement signal fit on the line, it must be ensured that the phase measurement is carried out correctly, i. H. the ambiguity of the phase range must be taken into account. Such consideration is also known and customary to the person skilled in the art. Multi-frequency measurements can be carried out for this. This has the advantage that the redundancy of the measurement is increased by the multi-frequency measurements, which in turn contributes to increased measurement accuracy.

The attenuation and / or time delay and / or phase change of the field between the at least two points in the at least one electrically conductive above-ground line is preferably measured.

Special features must be taken into account when selecting the frequency ranges for measuring the snow or ice cover on soils. Snow is a mixture of ice, air and water, the water content being negligible until just before the melt. However, if the invention is also to be used for the prewarning of meltwater flooding, it is important to also detect the liquid water content. Ice and water differ greatly in their dispersion characteristics in the dielectric constant, which makes it possible to distinguish the two by measuring the dielectric constant at different frequencies.

The dielectric constant of water for direct current is up to approx. 1 gigahertz and 20 ° C approx. 80. Ice, on the other hand, has its relaxation frequency at approx. 10 kHz, so that its dielectric constant approaches 103 kHz below and above 3.16 above 400 kHz ("Snow Dielectric Measurements", Adv. Space Res. Volume 9, No. 1, 1989). For the detection of snow or ice, measurements are therefore carried out at at least two frequencies at which the dielectric numbers differ. The measurement of ice and snow is further facilitated by the fact that they cause a very small damping of the measuring field.

For the measurement in the time domain, a time-limited wave packet is switched to the measuring line by a generator. At the end of the measuring line, the signal delayed by the soil moisture is routed to a receiver, for example through shielded cables. The signals are led from the generator and from the receiver to a measuring device in which, in addition to the damping, the time difference between the signals (ie the transit time) is also measured. The measured values obtained (attenuation, delay) are then converted into the dielectric constant and conductivity and then finally accordingly into the moisture content. For the measurement in the frequency domain, a sine wave is switched to the measuring line by a sine generator whose frequency can be selected. At the end of the measuring line, the signal, which is influenced, for example, by the soil moisture, is routed to a phase-correct receiver through shielded cables. Both from the generator and from the receiver, analogous to the time domain measurement, the signals are led to a measuring device in that in addition to the damping, the phase change is also determined. The measured values obtained (attenuation, phase change) are then converted into the dielectric constant and conductivity and then accordingly into the moisture content.

In both cases, the receiver can be integrated in the measuring device and the generators and / or receivers can be connected to the measuring line either directly when the primary transmission is switched off or via coupling elements.

In a multi-line measurement system, signal transmission is influenced by all lines, including those that are not directly connected to the generator or receiver for measurement. In order to reduce this disturbing influence and to improve the signal yield of the measuring line, all lines are provided with matching resistors at both ends. Electrical engineers call devices "adapted" if their input and / or output impedances are equal to the measuring line impedance. In the present case, the measuring line impedance depends, for example, on the unknown soil moisture. In order to achieve a good compromise between the impedance actually required for each measurement and the constant change of the impedances, the impedance of the measuring line can be chosen so that it corresponds to the average soil moisture. Further details, features and advantages of the present invention are explained below with reference to the drawing. Show it:

Fig. 1 shows a first embodiment of the invention

Device with interrupted primary transmission on the line used;

Fig. 2 shows a second embodiment of the invention

Device in which the measurements take place during the primary transmission on the line used; Fig. 3 shows a third embodiment of the invention

Device using a multi-line transmission system; 4, 4a, a fourth embodiment of the invention

Contraption; 5, 5a a fifth embodiment of the invention

Device for parallel connection of two lines; 6, 6a a sixth embodiment of the device according to the invention when using two lines of different polarity; 7a, 7b, 7c schematically the course of the field lines as a function of the distance and the polarity of the lines used; and FIG. 8 shows a seventh embodiment of the invention

Device when using two lines connected in series.

Corresponding parts of the device according to the invention are numbered with the same reference numerals in the figures. 1 shows a first embodiment of the device according to the invention with interrupted primary transmission on the line L used. Interrupted primary transmission means that the line L used, for example, in the normal case for the overland transmission of electricity, is used for a short time only for the measuring method according to the invention. This can be done either by decoupling the measuring line 1, for example by means of a switch, from the rest of the line L. However, it is also possible to shut down the entire line L for the short duration of the measurement.

All lines that are used for coupling the device according to the invention to the measuring line are shielded lines.

The line L is spanned by insulators I between electricity pylons M a few meters above the floor B. The actual measuring line 1, which hovers above the ground B to be measured, is connected to a generator 2 and a combined receiver and measuring device 3 via coupling elements 9, 10, which are each arranged at the beginning and at the end of the measuring line. The generator 2 is connected via a line 5 to the coupling element 9 at the start of the measuring line 1. At the end of the measuring line 1, the combined receiver and measuring device 3 is connected to the coupling element 10 via a line 7.

Via line 5, the measurement signal generated by generator 2 is fed into measurement line 1 and passes through it, whereby damping, a delay or a phase change, or a combination of the three, occurs through interaction of the field lines generated by the current through which current flows with ground B. experiences the aforementioned parameters. The signal is then recorded by the receiver 3 and fed into the measuring device combined with the original one Measuring signal, which passes from the generator to the receiver via a separate line 6, is compared, so that the damping, delay and phase change caused by the interaction of the field with the ground are determined.

The computational evaluation of the measured values determined by the measuring device is carried out in a data processing system 4 connected to the measuring device via a line 8, which in addition to the calculation and data acquisition can also be used to control the device (e.g. measuring times etc.).

If a direct coupling of the measuring device and the associated shutdown of the line L is undesirable, then, as shown in FIG. 2, the measurement signal can be modulated onto the line via frequency-selective coupling elements 9 and 10 during the primary transmission. In other words, the transmission of the exhibition signal and the primary transmission take place in a different frequency range, so that they do not interfere and can take place in parallel. The high-frequency locks 16 and 17, which are arranged in front of and behind the coupling elements 9 and 10, serve to prevent measurement errors and interference in primary operation. Otherwise, the embodiment shown in FIG. 2 essentially corresponds to that from FIG. 1.

If, as shown in FIG. 3 and it is usually the case, there is a further line L2 in addition to line L1, which represents the actual measuring line 1, the signal transmission is influenced not only by the actual measuring line 1, but also by the other lines L2. In order to reduce this disturbing influence and to improve the signal yield in the measuring line, the lines L2 not used for the measurement are connected at their respective ends Matching resistors 13 and 14 are provided, which are connected to line L2 via coupling elements 12 and 11. The impedance of line L2 at the input and output is adapted to the measurement line impedance via these resistors, so that the measurement line is quasi "suppressed".

However, the measuring line impedance depends, for example, on the moisture in the ground, so that it is difficult to adapt the line L2 impedance and theoretically it would have to be constantly changed. To prevent this, a line impedance is set that corresponds to the average soil moisture. In order to be able to make an adjustment that may be necessary, for example when changing the seasons, it is useful if resistors 15 and 16 are also provided on the generator 2 and on the receiver / measuring device 3, via which the impedance of the measuring line can be changed. This can be done, for example, during routine maintenance of the generator and the receiver / measuring device.

In the case of a single-line transmission line, such as, for example, a railway overhead line, as shown in FIG. 4, the necessary return line must take place via the ground, so that the

Generator 2 via a corresponding line 12 and that

Measuring device / receiver 3 are connected to the floor B via a line 11. All the generator current then flows through the bottom and the full generator voltage is then between the bottom B and the

Line L on. In such a case, the retarding or phase-changing effect of the soil is strongest and the field lines

F run from line L to floor B, as shown in Fig. 4a. If several lines are used, there are also various switching options. The bottom can still be used for the return line and two or more parallel lines can be connected for the measuring line. As a result, the measuring device will act on the floor in a wider strip below the lines, as can be seen, for example, from FIGS. 5 and 5a. Here, the lines L1 and L2 are connected in parallel via coupling elements 13 and 14 connected to the elements 9 and 10, so that the field lines lead from the lines to the ground and cover a larger area. This also increases the depth of penetration of the measuring field into the ground.

For the return of the generator current (return line), another parallel line can be used instead of the bottom. Then one speaks of a two-wire. In such a case, as shown in Fig. 6, only part of the generator current flows into the ground. The measurement effect becomes smaller and the total attenuation along the line is also significantly smaller. For longer measuring distances, the two-wire version should therefore preferably be used.

It is possible to apply voltage of different polarity to lines L1 and L2, so that the field lines still run through soil B, but from one line L1 to another line L2 (see FIG. 6a).

In the two-wire version, two or more lines connected in parallel can be used for the line and / or the return line, so that the effect of the floor but also the attenuation is weakened more. At the same time, however, the width of the measuring range and the depth of penetration into the soil also change. The measuring field can be influenced by the choice of the distance between the conductors (see Figs. 7a - 7c). As the distance between the lines increases, the penetration depth of the measuring field or field lines increases. I.e. With the permutation of the possible circuit arrangements in the case of multi-conductors, it is possible to achieve different measuring widths and different measuring depths. This also applies to wiring with different polarity of the lines.

This fact makes it possible to determine the extent of a blanket of snow spread over the ground.

Furthermore, the use of different arrangements increases the redundancy of the measurements, which increases the measurement accuracy.

At different temperatures, the lines lie at different heights above the ground, since the materials usually used, such as steel, vary greatly in length with the temperature. For example, aluminum, copper and steel expand when the temperature rises and a pipe made of them "sags", reducing the distance to the floor. However, this also changes the measuring field in the ground, so that a correction of a possibly occurring temperature effect on the measured values is possible when using different measuring arrangements. This procedure can also be used to determine whether the lines themselves are iced up. When using systems with multiple lines, there is the option of looping or ringing so that the measuring line is switched back and forth, which means that the receiver / measuring device and the generator can be located in the same place, so that long lines are not necessary between the generator and the receiver, which is advantageous for the signal quality and simplifies maintenance (cf. FIG. 8). In the simplest case, line L1 is connected via a Bridge 15 connected in series with the line L2, so that the coupling element 10 is arranged approximately at the same location as the coupling element 9 and the lines 6 and 7 between the generator, receiver and measuring line become short. Such a circuit is possible in particular in the case of overhead lines of the energy distribution systems, since these are often networks. Furthermore, the generator, receiver and measuring device can also be designed in one housing.

Claims

claims

1. A method for determining properties of the soil, in particular the moisture content, comprising the steps:

- Generation of a time-limited or permanent electromagnetic field in at least one electrically conductive above-ground line

AC voltage applied in such a way that the at least one field extends into the ground,

- Measurement of at least the running time of the one used to generate the time-limited electromagnetic field

Wave package and / or a change in

AC voltage parameters of the field between at least two points spaced apart in the longitudinal direction of the line in the at least one above-ground line,

Comparison of the at least measured transit time and / or the measured change in the AC voltage parameters between the at least two points in the at least one electrically conductive above-ground line

Defaults.

2. The method according to claim 1, characterized in that the

Damping and / or time delay and / or phase change of the field between the at least two points in the at least one electrically conductive above-ground line is measured.

3. The method according to any one of the preceding claims, characterized in that the at least one electrically conductive above-ground line is shut down for normal operation during the measurement.

4. The method according to any one of claims 1 to 3, characterized in that the at least one electrically conductive above-ground line during the measurement for your normal

Operation remains available.

5. The method according to any one of the preceding claims 2 to 4, characterized in that the change in damping and / or time delay and / or phase change of the field between the at least two points in the at least one electrically conductive above-ground line with calibrated and / or calculated Standard values is compared.

6. The method according to any one of the preceding claims, characterized in that the change in the field is measured in the frequency domain and / or time domain.

7. The method according to claim 6, characterized in that a

Frequency range between 1 kHz and 450 kHz and / or 1 to 1000 MHz is used for the measurement.

8. The method according to any one of the preceding claims, characterized in that the measurement at least two

Frequencies is performed.

9. Device for coupling to at least one electrically conductive above-ground line for determining properties of the soil, in particular the moisture content

- At least one generator for generating a time-limited or permanent AC voltage Connection to the at least one electrically conductive above-ground line,

at least one measuring device for recording the transit time of the wave packet used to generate the time-limited electromagnetic field and / or changing at least one parameter of the AC voltage.

10. The device according to claim 9, characterized in that the electrically conductive above-ground line one or more lines selected from the group consisting of overhead power lines, supply lines, above-ground telephone lines, rail traffic overhead lines,

Includes cable car lines.

11. The device according to claim 9 or 10, characterized in that the electrically conductive above-ground line comprises a single line and / or two-wire and / or multi-conductor.

12. Device according to one of claims 9 to 11, characterized in that the generator and / or the measuring device are connected via coupling elements to the at least one electrically conductive above-ground line.

13. The device according to one of claims 9 to 12, characterized in that high-frequency barriers before and after one

Measuring section on which at least one electrically conductive above-ground line are arranged.

4. Device according to one of claims 11 to 13, characterized in that the individual lines of a multi-conductor have matching resistances at the respective ends of the measuring section.