Direct current measurement directly at a current line of a DC supply grid

Abstract

The invention specifies a method for measuring a location-dependent current intensity value (I) of a current line (1, 1a, 1b) of a DC supply grid (60). In the method, the current line (1, 1a, 1b) is directly contacted by two measuring contacts (2a, 2b) of a voltage measuring unit (21) at a predetermined distance (d) between the measuring contacts (2a, 2b). An electrical voltage drop (Us) between the two measuring contacts (2a, 2b) is also measured. A current intensity (I) of an electric current flowing between the two measuring contacts (2a, 2b) in the current line (1, 1a, 1b) is determined based on the measured electrical voltage drop (Us) and the ohmic resistance (R, R1, R2) of the current line (1) between the two measuring contacts (2a, 2b). A current measuring device (20) is also described. A DC supply grid (60) for supplying current to electrically driven vehicles is also described.

Description

[0001] Description

[0002] DC current measurement directly on a power line of a DC power supply network

[0003] The invention relates to a method for measuring a location-dependent current value of a power line of a direct current supply network. Furthermore, the invention relates to a current measuring device. Furthermore, the invention relates to a direct current supply network for supplying power to electrically powered vehicles.

[0004] The measurement of current values ​​in DC power supply networks with free power lines, usually in the form of uninsulated power lines, in particular DC networks with catenary lines or overhead lines, is required to monitor correct operation and to take protective measures in the event of overloads, particularly in the event of a short circuit or earth fault. Nowadays, in a DC power supply network for vehicles, also referred to below as an overhead line network, the current is only measured in the protection device at the infeed to an overhead line. If the type of overhead line changes along the line, it can also be interesting to measure the current at different positions along the overhead line. The same applies to a "meshed or branched network" in which several infeeds supply one section of the network.

[0005] A conventional method for measuring direct currents uses a shunt resistor that is inserted into the circuit of the actual power supply line. The voltage drop across the shunt resistor is measured. According to Ohm's law, the measured voltage drop across a well-defined resistor corresponds to the current flowing through the well-defined resistor. An additional isolation amplifier is required to obtain a signal level that can be used for further analysis and to provide insulation between a circuit and a protection and / or control unit in order to shield extra-low voltage circuits connected at the output from the high voltage of the overhead line or the high voltage at the input. A shunt resistor is an additional component that is difficult to implement in direct current contact lines, particularly in overhead contact lines for rail vehicles.Therefore, a current measuring device is currently only used in switch cabinets in substations at the feed-in points of such a direct current contact line network.

[0006] As already mentioned at the beginning, current intensity in a direct current contact line network, in particular a contact line network or overhead line network, has so far been measured at the feed-in point, which, however, is not very meaningful for the values ​​of the current intensity of the currents in the direct current contact line network at the positions of the direct current contact line remote from the feed-in point.

[0007] There are also several sophisticated current measurement methods that utilize different effects of magnetic fields. The implementation of these methods is complicated because they require many special components, such as Hall sensors. In particular, so-called conversion transformers, which are required for measurements with Hall sensors and which are built around a power line, are not suitable for overhead lines. Since a free DC contact line, especially a free overhead line, moves when it passes a pantograph, the measurement can be disturbed if a Hall sensor is not precisely aligned. Therefore, this method is not particularly suitable for measurements on moving overhead lines.

[0008] Another possibility is based on temperature measurement with an infrared thermometer. However, this type of measurement method would require the temperature sensor to be positioned precisely and in an aligned manner, which cannot be reliably achieved for overhead lines that are set in motion by the passage of pantographs. Furthermore, it is not always possible to determine the current precisely from the measured temperature because environmental conditions such as wind and ambient temperature influence the conductor temperature of a conductive material in an overhead line. However, the most accurate determination possible of the current strength of a contact line or contact wire in an overhead line is important for protective devices. If an excessive current occurs due to a short circuit, a protective device must intervene reliably. If the current measurement is incorrect, the prescribed limit values ​​cannot be precisely adhered to.

[0009] The task is therefore to specify a method for the exact determination of location-dependent current values ​​in power lines of a direct current power network.

[0010] This object is achieved by a method for measuring a location-dependent current value of a power line of a direct current supply network according to patent claim 1, by a current measuring device according to patent claim 10 and by a direct current supply network for supplying power to electrically powered vehicles according to patent claim 13.

[0011] In the method according to the invention for measuring a location-dependent current value of a power line of a direct current supply network, preferably a direct current line network, the power line is directly contacted with two measuring contacts of a voltage measuring unit, preferably an isolating amplifier, at a predetermined position in the direct current supply network at a predetermined distance between the measuring contacts. For this purpose, the power line is electrically uninsulated at the positions where the measuring contacts electrically contact the power line in order to establish electrical contact between the power line and the two measuring contacts.

[0012] An at least partially electrically uninsulated power line has sections whose surface is free of insulating materials and can therefore be contacted by the aforementioned measuring contacts at any time and without further measures. To ensure that the uninsulated sections are still protected against short circuits, the power line, at least with those sections in which its surface is not electrically insulated from the environment by an insulating material, is arranged at a sufficient distance from the environment, preferably arranged at a sufficient distance from the ground or from objects in the environment, preferably suspended freely.Therefore, although there is insulation from the environment, the power line can still be easily contacted by the two measuring contacts due to the lack of insulation materials at the non-insulated points without modifications to the power line, in particular any possibly partially present insulation layer of the power line.

[0013] Furthermore, the voltage measuring unit measures an electrical voltage drop between the two measuring contacts. Based on the measured electrical voltage drop and the ohmic resistance of the power line between the two measuring contacts, the current flowing between the two measuring contacts in the power line is determined. Unlike conventional current measuring devices, the current-carrying conductor, whose current is to be measured, is used directly as a "shunt resistor."

[0014] Advantageously, current values ​​can be determined with spatial resolution in different sections of a feed area of ​​a direct current line network. Another advantage is that compliance with current limit values ​​in direct current lines can be reliably monitored and short circuits can be detected and localized. Their undesirable effects can be prevented by countermeasures, such as triggering a protective device or interrupting a circuit using such a protective device. In particular, current directions of individual currents can also be determined. Current directions can change, particularly in a direct current supply network for vehicles, especially rail vehicles, when vehicles feed current into the direct current supply network or draw current from the direct current supply network.Furthermore, a current measurement based on measuring a voltage drop across a resistor is particularly easy to implement and can therefore be implemented with little resource expenditure and at low cost compared to conventional measuring methods which are based, for example, on current measurement with Hall probes and can also be used for location-dependent current measurement.

[0015] The current measuring device according to the invention has two measuring contacts for directly contacting a power line of a power supply network or power line network with the two measuring contacts at a predetermined distance between the measuring contacts. Furthermore, the current measuring device according to the invention comprises a voltage measuring unit for measuring an electrical voltage drop between the two measuring contacts. In addition, the current measuring device according to the invention also has a current measuring unit for determining a current strength of a current flowing between the two measuring contacts in the power line on the basis of the measured electrical voltage drop and the ohmic resistance of the power line between the two measuring contacts. The current measuring unit preferably comprises a protective device or a protective relay which automatically carries out a protective reaction depending on a measured current strength.The current measuring device according to the invention shares the advantages of the method according to the invention for measuring a location-dependent current value of a power line of a direct current supply network. In particular, the resource expenditure for manufacturing, installing and operating the current measuring device according to the invention is advantageously reduced compared to the expenditure for manufacturing, installing and operating conventional arrangements for the same purpose. The direct current supply network according to the invention, preferably a direct current line network, for supplying power to electrically powered vehicles, preferably a contact line network, particularly preferably an overhead line network, has a plurality of substations, a plurality of feed switches per substation and a plurality of feed areas.Each feed switch is assigned a feed area, and each feed area is electrically connected to one or more assigned substations (several substations in the case of two- or multi-sided feed) via the assigned feed switch. Each feed area has a plurality of subsections that are assigned to different lane sections, in particular track sections. The DC power supply network according to the invention for supplying power to electrically powered vehicles has the current measuring device according to the invention. The DC power supply network according to the invention shares the advantages of the current measuring device according to the invention.

[0016] Some of the aforementioned components of the current measuring device according to the invention can be implemented wholly or partially in the form of software modules in a processor of a corresponding computing system of a current measuring device, in particular the current measuring unit. A largely software-based implementation has the advantage that even previously used computing systems of a conventional current measuring device can be easily retrofitted by means of a software update in order to operate in the manner according to the invention. In this case, the current measuring device must additionally be modified, as described above, in such a way that it has two measuring contacts which can be applied to a power line at a predetermined distance.

[0017] In this respect, the problem is also solved by a corresponding computer program product with a computer program that can be loaded directly into a computing system of a current measuring device, with program sections to carry out the step of determining a current strength of an electrical current flowing between the two measuring contacts in the power line when the program is executed in the computing system. Such a computer program product can, in addition to the computer program, optionally comprise additional components, such as documentation, and / or additional components, including hardware components, such as hardware keys (dongles, etc.) for using the software.

[0018] A computer-readable medium, such as a memory stick, a hard disk, or another portable or permanently installed data storage device, can be used for transport to the computer system and / or for storage on or in the computer system, on which the program sections of the computer program that can be read and executed by a computer system are stored. For this purpose, the computer system can, for example, have one or more cooperating microprocessors or the like.

[0019] The dependent claims and the following description each contain particularly advantageous embodiments and developments of the invention. In particular, the claims of one claim category can also be developed analogously to the dependent claims of another claim category and their description parts. Furthermore, within the scope of the invention, the various features of different embodiments and claims can also be combined to form new embodiments.

[0020] In one embodiment of the method according to the invention for measuring a location-dependent current value of a power line of a direct current supply network, the power line is designed as a substantially completely uninsulated power line. Advantageously, in this embodiment, the power line can be electrically contacted at any position by the two measuring contacts of the current measuring device. Particularly preferably, the power line comprises one of the following power line types:

[0021] - a catenary,

[0022] - an overhead line of an electricity network for stationary consumers.

[0023] The above-mentioned power line types have the advantage that they are completely insulated from the environment by the air due to a free suspension, but their surface is completely free of insulating materials, so that they can be contacted at any position.

[0024] A contact line is used to supply power to an electrified vehicle which has a pantograph. The contact line has a contact wire as a contact element to a pantograph, which is preferably suspended from holding cables via so-called hangers. The measuring contacts establish the electrical contact between the voltage measuring unit and the contact wire. Typical distances between the two measuring contacts are from a few tens of centimeters to a few meters. A contact wire usually has a so-called grooved contact wire, which has a basically circular cross-section, with two V-shaped grooves cut out in the upper half so that holding clamps can engage there.Advantageously, the two measuring contacts of the current measuring device according to the invention can be designed in such a way that they also engage in the V-shaped grooves, so that the measuring contacts do not impair ferry operation and contacting of the contact wire by a current collector of a vehicle.

[0025] An overhead line in a power grid for energy distribution to stationary consumers comprises an electrical line whose live conductors are routed through the air outdoors and are usually only insulated from each other and from the ground by the surrounding air. Typically, the conductors or conductor cables are supported by overhead line pylons, to which they are attached with insulators. The free accessibility of an overhead line at any location can advantageously be used to measure the current intensity of an electric current flowing through the overhead line or a conductor of the overhead line using the method according to the invention.

[0026] In one embodiment of the method according to the invention for measuring a location-dependent current value of a power line of a direct current supply network, the ohmic resistance of the power line between the two measuring contacts is determined on the basis of the predetermined distance and the knowledge of the specific resistance of a material of the power line. With a specific resistance of copper of 17.1 mΩ mm 2 / m results, for example, for a typical cross-section of a contact wire of 100 mm 2 a resistance of 0.17 mQ / m. Typical voltage drops of 60 mV / m result in a current of approximately 350 amperes for a distance of one meter between the two measuring contacts.

[0027] A power line, especially a contact wire, is subject to wear, which leads to a decrease in the cross-sectional area of ​​the contact wire and a corresponding increase in the ohmic resistance of a fixed-length conductor section over time. Such a change should be taken into account when measuring current.

[0028] In a preferred embodiment of the method according to the invention for measuring a location-dependent current value of a power line in a direct current power network, the electrical potential of the measurement signals at the two measuring contacts is converted by an isolating amplifier into a lower electrical potential which is compatible with a measuring range of the measuring electronics of the voltage measuring unit of the current measuring device. While the electrical voltage applied to the power line for overhead lines in direct current networks for rail vehicles, such as trams, is typically 1500 V or 750 V, the measuring range of the current measuring device or the voltage measuring unit of the current measuring device is at voltage values ​​in the low voltage range.Such values ​​can also be read by corresponding evaluation units of a control system of a protective device or a SCADA system (SCADA = Supervisory Control and Data Acquisition).

[0029] If the power line, as is usually the case with overhead lines, only comprises one conductor, the current intensity I is simply calculated using Ohm's law as

[0030] Where U s the electrical voltage measured between the two measuring contacts and R the resistance of the conductor section between the two measuring contacts.

[0031] If the power line on which the measuring contacts are arranged has a line type with several spatially separated components, which may also both have an electrical current flowing through them in parallel, it is sufficient if the measuring contacts only contact one of the components.

[0032] Such a power line preferably comprises a contact line, which has a contact wire as a contactable component and additionally a supporting cable through which current is also carried. In such a power line type, the measuring contacts are preferably arranged at a predetermined distance on one of the two conductors, particularly preferably on the contact wire. In the latter case, determining the current intensity I comprises determining the current intensity I i of the electrical current flowing between the two measuring contacts in the contact wire on the basis of the measured electrical voltage drop U sbetween the two measuring contacts and based on the ohmic resistance Ri of a section of the contact wire between the two measuring contacts.

[0033] Since the overhead line usually comprises not only a contact wire but also a parallel supporting cable on which the contact wire is suspended via so-called hangers, i.e. vertically oriented cables, in this variant a current intensity I of an electrical current flowing through the contact wire and the supporting cable of the overhead line between the two measuring contacts is determined on the basis of the ohmic resistance R2 of a section of the supporting cable between the two measuring contacts and the determined current intensity I i of the electrical current flowing between the two measuring contacts in the overhead wire.

[0034] Therefore, the total current I is the sum of the current I i of a first current flowing through the section between the two measuring contacts through the contact wire, and the current I2 of a second current flowing parallel to the first current through a section of the suspension cable between the two measuring contacts. The current I2 of the electric current flowing through the suspension cable is thus:

[0035] The total current or the current intensity of the total current I = I i

[0036] + I2 finally results in :

[0037] Advantageously, the total electrical current flowing through the individual components of a power line, in particular a contact line, with several separately arranged components can be taken into account when monitoring a power line network.

[0038] In a variant of the inventive method for measuring a location-dependent current value of a power line of a direct current supply network, the isolation amplifier is preferably arranged on a mast of the overhead line. The isolation amplifier can be arranged, similar to a mast disconnector panel, on a mast from which the overhead line is also suspended. Advantageously, no additional devices for positioning the isolation amplifier need to be installed on the track bed.

[0039] In one variant of the method according to the invention for measuring a location-dependent current strength value of a power line of a direct current supply network, the current strength is determined adjusted on the basis of determined local weather conditions. Local weather conditions, in particular the ambient temperature of the power line, the solar radiation on the power line, the humidity and the wind speed, can influence a resistance value of a power line and must be taken into account when determining a current strength of an electrical current flowing through a power line section because the location-dependent current strength is determined on the basis of knowledge of an ohmic resistance of a power line section between the two measuring contacts. The current measurement is advantageously made more precise by taking the weather conditions into account.

[0040] In addition to the measured air temperature, wind speed can also influence the temperature of the overhead line material. In particular, increased wind speed can cause a cooling effect.

[0041] Solar radiation also influences the temperature of an open power line. In addition to the surrounding air, the line itself is also heated. At a certain temperature, an equilibrium is formed between the incoming heat and the heat radiated and released by conduction or convection.

[0042] The already mentioned embodiments of the method according to the invention for measuring a location-dependent current value of a power line of a direct current power network can also be transferred analogously to the current measuring device according to the invention.

[0043] In particular, in one embodiment of the current measuring device according to the invention, the current measuring unit is configured to determine the ohmic resistance of the power line between the two measuring contacts based on the predetermined distance and knowledge of the specific resistance of a material of the power line. As already mentioned, a total current flowing through the individual components of a power line can be calculated in the manner illustrated by formulas (1) to (4).

[0044] Also analogous to the corresponding embodiment of the method according to the invention, the voltage measuring unit of the current measuring device according to the invention has an isolating amplifier configured to convert the electrical potential of the measurement signals at the two measuring contacts into a lower electrical potential that is compatible with the measuring electronics of the voltage measuring unit of the current measuring device. The isolating amplifier is preferably arranged on the mast for the power line, in the case of current measurement on a contact line, a contact line mast.

[0045] In a preferred embodiment of the current measuring device according to the invention, the two measuring contacts are designed such that the predetermined distance between the measuring contacts can be freely selected within a predetermined distance interval. Advantageously, the distance can be selected such that a voltage drop measured between the two measuring contacts lies within a value range suitable for further processing or evaluation of the measurement signals. Furthermore, the distance between the measuring contacts can also be selected depending on location-specific conditions that only permit certain distances between the measuring contacts.For a flexible adjustment of the distance between the two measuring contacts, the measuring contacts are preferably electrically connected via flexible electrical lines to the voltage measuring unit, in particular the isolating amplifier of the current measuring device according to the invention, wherein the sum of the lengths of the two flexible electrical lines determines the maximum distance between the two measuring contacts.

[0046] In a preferred embodiment of the current measuring device according to the invention, the current measuring unit is configured to determine the current in an adjusted manner based on determined local weather conditions. As already explained in connection with the method according to the invention for measuring a location-dependent current value of a power line in a direct current power network, knowledge of the weather conditions allows an electrical resistance of a power line section, whose value depends on a weather condition, to be determined more precisely, thus improving the accuracy and reliability of the current measurement.

[0047] For this purpose, the current measuring device according to the invention preferably comprises a weather observation unit which is designed to determine local weather conditions. For this purpose, the weather observation unit of the current measuring device according to the invention is, similar to the isolating amplifier already mentioned several times, preferably arranged on a power line mast, or in the case of a current measurement on a contact line, on a contact line mast or overhead line mast. Advantageously, no additional masts for positioning components of the current measuring device need to be arranged near the power line to be monitored. The local weather conditions determined by the weather observation unit of the current measuring device according to the invention preferably comprise a temperature and / or a wind speed.

[0048] The invention is explained in more detail below with reference to the accompanying figures using exemplary embodiments. They show:

[0049] FIG 1 is a schematic diagram of a conventional direct current network for supplying power to rail vehicles,

[0050] FIG 2 shows a schematic representation of a current measuring device according to a first embodiment of the invention,

[0051] FIG 3 is a flowchart illustrating a method for measuring a location-dependent current value of a power line of a direct current power network according to an embodiment of the invention,

[0052] FIG 4 is a schematic representation of a current measuring device according to a second embodiment of the invention,

[0053] FIG 5 is a flowchart illustrating a method for measuring a location-dependent current value of a contact line of a direct current contact line network according to an embodiment of the invention,

[0054] FIG 6 is a schematic representation of a direct current supply network for supplying power to rail vehicles according to an exemplary embodiment of the invention. FIG 1 is a schematic representation of a conventional direct current supply network 10 for rail vehicles. The direct current supply network 10 comprises a plurality of substations 6 (for the sake of clarity, only two substations are shown in FIG 1) which use a transformer 7 to transform a high voltage from a high-voltage network into a lower electrical voltage, for example a low voltage. Furthermore, the conventional direct current supply network 10 shown in FIG 1 comprises rectifiers 8 which are respectively assigned to the substations 6 and with which the low voltage present as alternating voltage is converted into a direct voltage.Part of the conventional direct current supply network 10 are also feed switches 5 assigned to the individual substations 6, with which a direct voltage is applied to a feed area 11a, 11b with several power lines 1, in particular overhead lines, which are arranged over different track sections 9. Several feed switches 5 can be assigned to a substation 6. FIG. 1 shows three feed switches 5 per substation 6 (left in the image) and four feed switches 5 per substation 6 (right in the image).

[0055] FIG 1 also shows a conventional current measuring device 3 on a feed switch 5 of the feed area 11a shown on the left in the figure (a further feed area 11b is shown on the right in the figure, the two feed areas 11a, 11b are separated from one another by a dashed line in the middle of the figure), wherein the conventional current measuring device 3 has a shunt resistor 4 which is connected in series to the power supply line in which the feed switch 5 is arranged. Since the conventional current measuring device 3 is located on the feed switch 5, the conventional current measuring device 3 can only measure the balance of the currents of the individual subsections of the feed area 11a assigned to the relevant feed switch 5. It is therefore not possible to judge from the current measurement at the feed switch 5 which subsection of the assigned feed area 11a transmits which current.The currents flowing in the subsections are additionally influenced by rail vehicles, which may be located in different subsections of the respective feed-in area 11a, 11b. The current intensity in the overhead lines is influenced by the rail vehicles depending on whether they are drawing current from the DC power supply network 10, for example during accelerated or uniform movement, or whether they are feeding current into the DC power supply network 10, for example during a braking maneuver.

[0056] In FIG 2, a current measuring device 20 according to an embodiment of the invention is shown schematically.

[0057] The current measuring device 20 illustrated in FIG 2 comprises two measuring contacts 2a, 2b for directly contacting a power line 1b (left in the picture) of a direct current line network for stationary consumers with the two measuring contacts 2a, 2b at a predetermined distance d of the measuring contacts 2a, 2b from one another.

[0058] The current measuring device 20 has, as a voltage measuring unit, an isolating amplifier 21 for measuring an electrical voltage drop U s between the two measuring contacts 2a, 2b, which contact the power line 1b, and for converting the measuring signals detected with a high potential at the two measuring contacts 2a, 2b into measuring signals with a low potential.

[0059] Part of the current measuring device 20 according to the invention is also a current measuring unit 22, in particular a protective device or protective relay. The current measuring unit 22 is configured to determine a current I of a current flowing between the two measuring contacts 2a, 2b in the power line 1b based on the measured electrical voltage drop U s and the ohmic resistance R of the power line 1b between the two measuring contacts 2a, 2b according to formula (1). FIG. 3 shows a flowchart 300 illustrating a method for measuring a location-dependent current value I of a power line 1b of a direct current power grid for stationary consumers according to an exemplary embodiment of the invention.

[0060] In step 3.1, the power line 1b is directly contacted with two measuring contacts 2a, 2b, which are electrically connected to an isolating amplifier 21 of a current measuring device 20, at a predetermined distance d between the measuring contacts 2a, 2b.

[0061] Subsequently, in step 3 . II, an electrical voltage drop U s measured between the two measuring contacts 2a, 2b.

[0062] Finally, in step 3 . III, based on the measured electrical voltage drop U s and the known ohmic resistance R of the current line 1b between the two measuring contacts 2a, 2b according to formula (1) a current value I for an electrical current flowing between the two measuring contacts 2a, 2b is determined.

[0063] In FIG 4, a current measuring device 20 according to an alternative embodiment of the invention is shown schematically.

[0064] The S scenario shown in FIG 4 differs from the S scenario shown in FIG 2 in that in FIG 4 a current intensity I of an electric current is measured which flows through a contact line la which has a contact wire laa and a suspension cable lab connected in parallel to the contact wire laa.

[0065] The current measuring device 20 shown in FIG 4 comprises two measuring contacts 2a, 2b for directly contacting the contact wire 1a of the contact line 1a at a predetermined distance between the measuring contacts 2a, 2b.

[0066] The current measuring device 20 has a voltage measuring unit 21 for measuring an electrical voltage drop U s between the two measuring contacts 2a, 2b, which contact the contact wire laa.

[0067] The current measuring device 20 has an isolating amplifier 21 as a voltage measuring unit. The isolating amplifier 21a converts the measurement signals detected with a high potential at the two measuring contacts 2a, 2b into measurement signals with a low potential.

[0068] Part of the current measuring device 20 according to the invention is also a current measuring unit 22. The current measuring unit 22 is designed to determine a current I of a current which results from the sum of the two currents I i, I 2 flowing through the contact wire 1aa and the suspension cable 1a. The current I is determined on the basis of the measured electrical voltage if U sand on the basis of an ohmic resistance Ri of a section of the contact wire laa between the two measuring contacts 2a, 2b and an ohmic resistance R2 of a section of the suspension cable lab which runs parallel to the section of the contact wire laa between the two measuring contacts 2a, 2b. The ohmic resistances Ri, R2 of the sections of the contact wire laa and the suspension cable lab can be calculated on the basis of knowledge of the specific resistance of the materials of the contact wire laa and the suspension cable lab as well as on the basis of the known cross-sections and on the basis of the known distance d between the two measuring contacts 2a, 2b. The values ​​of the electrical current intensities through the contact wire laa and through the suspension cable are given by formulas (2) and (3). The sum I of the two current intensities Ii, I2 is also given by formula (4).FIG 5 shows a flow chart 500 which illustrates a method for measuring a location-dependent current intensity value I of a contact line 1a of a direct current contact line network according to an embodiment of the invention.

[0069] In step 5.1, a contact wire 1a of a contact line 1a is directly contacted with two measuring contacts 2a, 2b of a voltage measuring unit 21 at a predetermined distance d between the measuring contacts 2a, 2b.

[0070] Subsequently, in step 5 . II, an electrical voltage drop U s measured between the two measuring contacts 2a, 2b.

[0071] Subsequently, in step 5 . III, based on the measured electrical voltage drop U sand the known ohmic resistance Ri of the contact wire laa of the contact line la between the two measuring contacts 2a, 2b, a value of a current intensity I i of a current flowing between the two measuring contacts 2a, 2b in the contact wire laa of the contact line la is determined according to formula (2).

[0072] Furthermore, in step 5.IV, on the basis of the determined current intensity value I i of a current flowing between the two measuring contacts 2a, 2b in the contact wire laa of the contact line 1, the knowledge of the ohmic resistance Ri of the contact wire laa of the contact line la between the two measuring contacts 2a, 2b and on the basis of the knowledge of a corresponding resistance value R2 of the section of a suspension cable lab of the contact line 1 that is guided parallel to the contact wire laa, a value of a current intensity I2 is determined according to formula (3).

[0073] Finally, in step 5. V, a value of a current intensity I of a total current flowing through the contact wire 1aa and the suspension cable lab between the two measuring contacts 2a, 2b is determined according to formula (4). FIG. 6 shows a schematic representation of a direct current supply network 60 for supplying power to rail vehicles on a rail network according to an exemplary embodiment of the invention. The direct current supply network 60 shown in FIG. 6 is constructed in a similar manner to the direct current supply network 10 shown at the beginning of FIG. 1.

[0074] The DC power supply network 60 shown in FIG. 6 differs from the conventional DC power supply network 10 shown in FIG. 1 in that current measuring devices 20 according to an exemplary embodiment of the invention are arranged in the individual subsections of the feed-in areas 11a, 11b of the DC power supply network 60. The current measuring devices 20 have the structure illustrated in FIG. 4. In particular, the current measuring devices 20 are distributed throughout the entire DC power supply network 60, so that local current values ​​can be measured in individual subsections.

[0075] Finally, it is pointed out once again that the methods and devices described above are merely preferred embodiments of the invention and that the invention can be varied by those skilled in the art without departing from the scope of the invention, insofar as it is defined by the claims. For the sake of completeness, it is also pointed out that the use of the indefinite articles "a" or "an" does not exclude the possibility that the features in question may be present in multiple copies. Likewise, the term "unit" does not exclude the possibility that it consists of several components, which may also be spatially distributed.

[0076] Regardless of the grammatical gender of a particular term, persons with male, female or other gender identity are included.

Claims

Patent claims 1. A method for measuring a location-dependent current value (I) of a power line (1, 1a, 1b) of a direct current supply network (60), comprising the steps: - direct electrical contacting of the power line (1, 1a, 1b) with two measuring contacts (2a, 2b) of a voltage measuring unit (21) at a predetermined distance (d) between the measuring contacts (2a, 2b), - Measuring an electrical voltage drop (U s ) between the two measuring contacts (2a, 2b) by the voltage measuring unit (21), - Determining a current intensity (I) of an electrical current flowing between the two measuring contacts (2a, 2b) in the power line (1, 1a, 1b) on the basis of - the measured electrical voltage drop (U s ) and - an ohmic resistance (R, Ri, R2) of the power line (1, 1a, 1b) between the two measuring contacts (2a, 2b).

2. Method according to claim 1, wherein the power line (1, 1a, 1b) is designed as an at least partially uninsulated power line and the power line (1, 1a, 1b) contacts the two measuring contacts (2a, 2b) at uninsulated contact points of the power line (1, 1a, 1b).

3. Method according to one of the preceding claims, wherein the power line (1, 1a, 1b) is designed as an uninsulated power line and comprises one of the following power line types: - a contact line (la), - an overhead line (1b) of an electricity network for stationary consumers.

4. Method according to one of the preceding claims, wherein the ohmic resistance (R, Ri, R2) of the section of the power line (1, 1a, 1b) between the two measuring contacts (2a, 2b) is determined on the basis of the predetermined distance (d) and the knowledge the specific resistance of a material of the power line (1, 1a, 1b) is determined.

5. Method according to one of the preceding claims, wherein the voltage measuring unit (21) has an isolating amplifier which converts an electrical potential of measuring signals at the two measuring contacts (2a, 2b) into a lower electrical potential which is connected to a measuring range of a measuring electronics for measuring the voltage drop (U s ) is compatible.

6. Method according to one of the preceding claims, wherein - the power line (1, 1a, 1b) has a contact line (1a) and the contact line (1a) has a contact wire (1aa) and a suspension cable (1b), - the measuring contacts (2a, 2b) are arranged on the contact wire (1aa) at a predetermined distance (d), and - determining the current intensity (I) determining the current intensity (Ii) of the electrical current flowing between the two measuring contacts (2a, 2b) in the contact wire (1aa) on the basis of the measured electrical voltage drop (U s) between the two measuring contacts (2a, 2b) and based on the ohmic resistance (Ri) of the contact wire (laa) between the two measuring contacts (2a, 2b).

7. Method according to claim 6, wherein the determination of the current intensity (I) comprises determining a current intensity (I) of an electric current flowing through the contact wire (laa) and the supporting cable (lab) of the contact line (la) between the two measuring contacts (2a, 2b) on the basis of - the ohmic resistance (Ri) of the contact wire (laa) between the two measuring contacts (2a, 2b), - the ohmic resistance (R2) of the suspension cable (lab) between the two measuring contacts (2a, 2b) and - the determined current intensity (Ii) of the electric current flowing between the two measuring contacts (2a, 2b) in the contact wire (laa).

8. Method according to one of the preceding claims, wherein the determination of the current intensity (I, Ii) is adjusted on the basis of determined local weather conditions.

9. The method according to claim 8, wherein the local weather conditions comprise an ambient temperature of the power line (1, 1a, 1b) and / or a wind speed and / or an intensity of solar radiation on the power line (1, 1a, 1b).

10. Current measuring device (20) comprising: - two measuring contacts (2a, 2b) for directly contacting a power line (1, 1a, 1b) of a direct current supply network with the two measuring contacts (2a, 2b) at a predetermined distance between the measuring contacts (2a, 2b), - a voltage measuring unit (21) for measuring an electrical voltage drop (U s ) between the two measuring contacts (2a, 2b) , - a current measuring unit (22) for determining a current intensity (I, Ii) of a current flowing between the two measuring contacts (2a, 2b) in the power line (1, 1a, 1b) on the basis of - the measured electrical voltage drop (U s ) and - an ohmic resistance (R, Ri, R2) of the power line (1, 1a, 1b) between the two measuring contacts (2a, 2b).

11. Current measuring device according to claim 10, wherein the voltage measuring unit (21) has an isolating amplifier which is designed to convert an electrical potential of measuring signals at the two measuring contacts (2a, 2b) into a lower electrical potential which is connected to a measuring range of a measuring electronics of the voltage measuring unit (21) for measuring the electrical voltage drop (U s ) is compatible.

12. Current measuring device according to one of claims 10 or 11, wherein the current measuring unit (22) is configured to determine the current intensity (Ii, I) adjusted on the basis of determined local weather conditions.

13. A direct current supply network (60) for supplying power to electrically powered vehicles, comprising: - a plurality of substations (6) , - a plurality of feeder switches (5) per substation (6), - a plurality of feed-in areas (11a, 11b), wherein each substation (6) is assigned a feed-in area (11a, 11b) and each feed-in area (11a, 11b) has a plurality of subsections assigned to different lane sections, wherein each feed switch (5) is assigned a subsection of a feed-in area (11a, 11b) and a respective subsection is electrically connected to an assigned substation (6) via the assigned feed switch (5), - a current measuring device (20) according to one of claims 10 to 12.

14. Computer program product, with a computer program which can be loaded directly into a memory unit of a current measuring device (20), preferably according to one of claims 10 to 12, with program sections to carry out the step of determining a current intensity (I) of an electrical current flowing between the two measuring contacts (2a, 2b) in the power line (1, 1a, 1b) of the method according to one of claims 1 to 9 when the computer program is executed in the current measuring device (20).

15. Computer-readable medium, comprising instructions on which program sections executable by a computer unit are stored, in order to carry out the step of determining a current intensity (I) of an electrical signal flowing between the two measuring contacts (2a, 2b) in the power line (1, 1a, 1b). Stream of the method according to one of claims 1 to 9 when the program sections are executed by the computer unit.

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