Method and device for detecting an arc at a sliding contact between a current-carrying conductor and a high-voltage power transmission system

Abstract

The invention relates to a method and a device for detecting an arc in a high-voltage power transmission system (11), in which electrical energy is transmitted via a high-voltage conductor (17). The electrical energy is transmitted in particular to a current collector system of traffic systems such as a pantograph (13) on a locomotive. In the method, a) the change in the operating current through a conductor, in particular a high-voltage line, said change being caused by an arc or b) the change in the voltage at the cable shield of the conductor, said change being caused by an arc, or c) the magnetic field, which changes over time, caused by an arc in the immediate vicinity of the conductor are analysed and evaluated.

Description

[0001] Method and device for detecting an electric arc at a sliding contact between a current-carrying conductor and a high-voltage power transmission system

[0002] Field of the invention

[0003] The present invention relates to a method and a device for detecting an arc at a sliding contact between a current-carrying conductor and a high-voltage power transmission system for transmitting electrical energy to a vehicle.

[0004] State of the art

[0005] Transportation systems (railways, streetcars, trams, trolleybuses) draw their power from a high-voltage electrical conductor via a pantograph system. This sliding contact is therefore unsafe. The pantograph can lose mechanical contact with the overhead wire, which usually leads to an arc. This situation must be recognized so that operational measures to limit damage can be initiated in a timely manner.

[0006] Reliable detection of arcs helps to avoid dangerous situations, damage and service interruptions by taking the right measures. Such measures can include, for example, increasing the contact pressure, immediately shedding the load or lowering the pantograph. Arcs are a particularly dangerous situation when the train is at a standstill, for example if the pantograph loses its mechanical contact with the contact wire, which can occur due to a reduction in the contact force, e.g. if snow loads the pantograph. This condition can subsequently lead to damage and, in extreme cases, to the melting of the contact wire. At the same time, the pantograph system is also damaged. Melting of the contact wire endangers the life and limb of people in the vicinity and in any case means a lengthy service interruption, which must be prevented.

[0007] Arcing typically occurs during ferry operation when the pantograph temporarily or intermittently loses direct contact with the overhead wire due to vibrations or oscillations of the overhead wire. This manifests itself in visible sparks between the overhead wire and the pantograph. Excessive arcing is particularly problematic when overhead wires are icy or dirty. Arcing can also occur more frequently if the contact surface of the pantograph system is worn, dirty, or damaged. Due to the fluctuating current, electrical arcing can also cause radio interference, which must also be avoided.

[0008] An arc consists of an electrically conductive plasma between two contact surfaces, which heats itself up and thus maintains itself through the flow of current. The impedance of a burning arc changes greatly and randomly over time due to various influences, affecting the current flow. Therefore, a high-energy, broadband disturbance is impressed on the flowing operating current. The disturbance signal has the characteristics of thermal noise. The changing current leads to voltage feedback on the power grid. Both effects, the current disturbance and the voltage feedback, can be detected and evaluated using suitable sensors. In any case, the characteristics of the impedances in the circuit, which influence these disturbance signals and deform their frequency content, must be taken into account.

[0009] Unwanted arcs, i.e., potentially damaging or hazardous to humans, are also known to occur in other areas, such as high-performance distribution and switchgear systems. However, the causes of arcs, the possible shielding against external influences, and the options for circuit-based countermeasures often differ fundamentally from those of a current collector system in a transportation facility.

[0010] For example, arcs in distribution and switchgear systems tend to develop gradually due to material aging or conductive contamination, which can lead to short circuits or poor connections. This, in turn, leads to interrupted or nearly interrupted phase conductors, which can then cause a so-called serial arc fault or, in conjunction with another phase conductor, a so-called parallel arc fault.

[0011] In contrast, arcs occur more frequently in a current collector system of a traffic system and are often caused by abrupt external mechanical influences rather than by material aging or conductive contamination, e.g. by vibrations or forces acting on the current collector (e.g. by snow) which cause a sudden interruption of the mechanical connection between the current collector and the overhead line.

[0012] Furthermore, a sensor array for detecting arcs in distribution and switchgear systems can typically be positioned close to the event (close to the short circuit), whereas a sensor array for detecting an arc on a sliding contact of a vehicle can often only be placed several meters away from the event. This further dampens the effects of the arc, requiring different sensor technology (e.g., fundamentally different frequency measurements).

[0013] In addition, a current collector system in a traffic system is designed as a high-voltage single-phase system. Unlike arc protection circuits for distribution and switchgear systems, there is no neutral conductor, which typically makes the adaptation of solutions for distribution and switchgear systems, which often allow for greater circuit complexity, considerably more difficult or even impossible.

[0014] A further obstacle is the fundamentally different voltage ranges compared to a pantograph system in a traffic system. For example, in high-performance distribution and switchgear systems, the problem of arcing faults can be addressed using low-voltage circuit breakers. Such circuit breakers are configured to monitor the current flowing through them and to interrupt the electrical current if current limit values ​​are exceeded or undershot. Due to the high voltage applied to the contact wire or the pantograph of the traffic system, such a direct coupling to the operating current and thus the use of circuit breakers familiar from distribution and switchgear systems is not easily possible. In addition to a fundamentally different choice of circuit breaker type, the downstream circuit orSignal processing must be fundamentally reconditioned to consider application in a high-voltage power transmission system of a traffic facility.

[0015] An arc fault detection unit for use in high-performance distribution and switchgear systems is known, for example, from WO 2017 / 207535 A1. However, this arc fault detection unit is designed for a three-phase AC electrical circuit with three phase conductors and one neutral conductor. For this reason in particular, as well as for the other reasons mentioned above, the solution is not suitable for use in a high-voltage power transmission system of a transportation facility.

[0016] Another known method for detecting arcs in a distribution or switchgear system is based on monitoring current peaks and comparing the data corresponding to these measured current peaks with preselected data indicating an arc fault. However, such current peaks, as described, for example, in EP 1 103057 B1, have not been detected in a high-voltage power transmission system of a transportation facility. Furthermore, it is known, for example, to detect partial discharges arising in the insulation of high-voltage cables themselves, although a major problem here is often initially locating the location of the partial discharge. Such partial discharge measurements are typically used to diagnose the maintenance condition of the cable, but must be differentiated from the detection of "open" arcs, such as those caused by a contact break between the overhead line and the pantograph.Both the purpose and possible detection methods are fundamentally different. For example, in the case of an open arc caused by poor contact between the overhead line and the pantograph, localization is not necessary because the location of the arc is known. Accordingly, localization techniques typical for detecting partial discharges, such as time-domain reflectometry and time-domain signal analysis, tend to be inconvenient for determining an open arc within the meaning of the invention. Furthermore, typical boundary parameters such as measurement frequencies, circuit architecture, and applicable sensors are fundamentally different. For example, testing equipment, grounding options, and compensating currents are used to determine partial discharges, which, in turn, cannot be readily used to construct an arc sensor to detect an arc between the overhead line and the pantograph.The detection of partial discharges is described, for example, in CN 104459492 B.

[0017] Task

[0018] The object of the present invention is to provide a method and a device for the reliable detection of arcs occurring so that the correct measures, for example switching off the circuit, can be initiated automatically (at an early stage).

[0019] Description

[0020] According to the invention, the object is achieved by a method for detecting an arc at a sliding contact between a current-carrying conductor (e.g. contact wire, conductor rail) and a high-voltage power transmission system which is designed to provide a transmission of electrical energy to a vehicle (e.g. a transport system such as a railway, streetcar, tram, trolleybus, etc.), wherein electrical energy is transmitted from the current-carrying conductor via a high-voltage conductor of the high-voltage power transmission system (to the vehicle). The electrical energy is transmitted in particular to a current collector system of transport systems such as a pantograph on a locomotive. In the method, either a) the change in the operating current caused by an arc through a conductor, in particular a high-voltage line (e.g.the high-voltage conductor of the high-voltage power transmission system), or b) the change in voltage at the cable shield of the conductor caused by an arc, or c) the time-varying magnetic field in the immediate vicinity of the conductor caused by an arc, are analyzed and evaluated so that the power supply of the power transmission system can be switched off in time to avoid further damage.

[0021] Ideally, the occurrence of an arc must be detected as early and reliably as possible. In a power transmission system, this requires checking or monitoring the electrical energy in the line for any changes. The presence of a change in the electrical energy in the line can be determined by a change in either the operating current through the conductor, the voltage across the line, or the magnetic field in the immediate vicinity of the conductor. Analyzing and evaluating at least one of these three parameters enables early detection of an arc and shutdown of the power supply to prevent damage.

[0022] Preferably, the high-voltage line is at least partially covered with a cable shield. The cable shield on the line may be required if the voltage on the line is to be measured.

[0023] In a preferred embodiment, the cable shield of the high-voltage conductor is connected to ground at one end, and the voltage is tapped at the cable shield of the high-voltage conductor. Connecting the high-voltage conductor to ground grounds the high-voltage line. A surge arrester can then be attached to one end of the high-voltage conductor, which taps the voltage at the cable shield. This, in turn, leads to reliable voltage measurement at the cable shield of the high-voltage conductor.

[0024] In a further preferred embodiment, the magnetic field is detected at a short distance from the high-voltage conductor by one or more magnetic field sensors or by a Rogowski coil. The change in electrical energy in the high-voltage conductor due to the occurrence of an arc leads, among other things, to a change in the magnetic field around the high-voltage conductor. This change in the magnetic field can be detected and read by magnetic field sensors. Alternatively, a Rogowski coil can also be provided for this purpose. The advantage of the Rogowski coil is that it is able to detect high frequencies, especially above 10 kHz. The interference signal that appears in the high-voltage conductor due to an arc usually has frequencies greater than 10 kHz. Therefore, the use of a Rogowski coil is particularly suitable for detecting interference signals.

[0025] Advantageously, the current is measured using a non-contact current sensor or current transformer. This non-contact current measurement eliminates external interference with the electrical energy in the high-voltage conductor, ensuring safety. Since the arc must be detected as early as possible, the measurement must be sensitive to small changes. This, in turn, requires high measurement accuracy, and external interference with the measurement can be avoided with non-contact measurement.

[0026] Advantageously, the measurement methods according to procedures a), b) or c) generate a noise signal which is analyzed and evaluated.

[0027] The evaluation is preferably based on at least two different measurement methods according to procedures a), b), or c). The measurement methods according to procedures a), b), and c) can be applied in parallel. The use of at least two of these three measurement methods increases the reliability of the measurement by providing information from at least two different sources.

[0028] The evaluation is preferably performed by an electronic acquisition unit that samples the signals at a minimum frequency of 100 kHz after they have been appropriately filtered using analogue methods. The electronic acquisition unit enables further processing and evaluation of the recorded analogue signals. Sampling the analogue signals at a minimum frequency of 100 kHz ensures a reading rate that allows for early detection of the arc.

[0029] Ideally, the signals are mathematically processed and evaluated. Mathematical processing allows the signals to be processed in such a way that their evaluation can be performed more quickly. Applying predefined mathematical models to the measured signals leads to the desired parameters being achieved in the shortest possible time.

[0030] Preferably, the evaluation is carried out by an electronic circuit which, after suitable filtering and division into frequency bands, measures the energy content in the individual frequency bands and issues an alarm signal when an adjustable threshold is exceeded.

[0031] Preferably, the frequency range of the measured current or voltage above 10 kHz is analyzed and evaluated. Signal noise caused by the formation of an arc is particularly detectable in the high-frequency range above 10 kHz. Limiting the readout range to this frequency range makes reading and analysis more efficient and faster.

[0032] Advantageously, the frequency range of the measured current or voltage below 10 kHz is filtered, preferably using a high-pass filter. By filtering the range below 10 kHz, only the information above 10 kHz is available. Since the information about the formation of an arc tends to be present in this frequency range, arc detection can be performed faster and more reliably. A high-pass filter provides a way to automatically filter a lower frequency range and thus exclude it from further processing.

[0033] A further aspect of the invention relates to a device for detecting an arc at a sliding contact between a current-carrying conductor and a high-voltage power transmission system designed to provide a transmission of electrical energy to a vehicle. In the power transmission system, current (transmitted by the current-carrying conductor) is transmitted to the vehicle via a high-voltage conductor of the high-voltage power transmission system that is at least partially provided with a cable shield. In particular, the high-voltage conductor is connected to a current collector system of traffic equipment, such as a pantograph on a locomotive.The device comprises a measuring device either for measuring the change in the operating current through a conductor, in particular a high-voltage line, caused by an arc, for measuring the change in the voltage at the cable shield of the conductor caused by an arc, or for measuring the time-varying magnetic field in the immediate vicinity of the conductor caused by an arc.

[0034] The device is based on the idea that the formation of an arc in a power transmission system causes a change in the operating current through the conductor, in the voltage at the conductor's cable shield, and in the magnetic field in the immediate vicinity of the conductor. By detecting one of these changes, the formation of an arc can be determined. It is important to detect the arc and thus the resulting change in current or voltage as early as possible. The device according to the invention has a measuring device for measuring the change in voltage or current in the conductor. The information obtained by the measuring device allows the detection of an arc.

[0035] In a preferred embodiment, the measuring device comprises a current sensor or a coil for voltage measurement, in particular a Rogowski coil. The current sensor is responsible for measuring the current and can detect a change in the current. The voltage in the conductor is preferably determined by means of a voltage measurement. The use of a Rogowski coil for voltage measurement has a particular advantage, as it can detect frequencies above 10 kHz very well. Since interference signals in voltage measurements are expected at higher frequencies above 10 kHz, the Rogowski coil is particularly well suited for measuring the voltage in a device according to the invention.

[0036] Advantageously, the measuring device includes a filter that filters a frequency range of the measurement. With such a filter, a frequency range that is not of interest can be excluded and simply ignored. Only the frequency range to be examined and evaluated is considered for the evaluation.

[0037] The filter is preferably a high-pass filter that filters frequencies below 10 kHz. The high-pass filter is particularly well-suited for eliminating signals below a certain frequency limit. Since the interference signals have a frequency of at least 10 kHz, filtering the frequency below 10 kHz with a high-pass filter can reduce the measurement to the relevant portion. This leads to faster and more reliable processing of the measurement data and thus also to faster detection of an arc.

[0038] Preferably, the high-voltage conductor is electrically grounded. In everyday use, the conductor is subject to electrical current and voltage. Grounding the conductor eliminates the danger posed by its electrical charge. Description of the invention

[0039] The invention is described in more detail below with reference to the accompanying figures. They show:

[0040] Figure 1 shows a schematic view of a high-voltage power transmission system 11. A pantograph 13 is provided for transmitting electrical energy from a contact wire (not shown in the figure). The pantograph 13 can transmit the electrical energy from the contact wire to a high-voltage line 17 of a traffic system. The pantograph 13 is attached to the traffic system, and an insulator can be arranged between the pantograph 13 and the traffic system 15 to prevent the entire traffic system 15 from being energized. The power transmission system 11 comprises a transformer 15, which is supplied with power from the contact wire. A shielded high-voltage line 17 is arranged between the pantograph 13 and the transformer 15 as a power transmission means.The high-voltage line 17 is shielded by means of a cable shield, wherein the cable shield is formed by a layer which surrounds the line 17 and whose material is electrically non-conductive.

[0041] For example, the high-voltage power transmission system 11 is designed for a voltage of more than 1000 volts AC or more than 1500 V DC.

[0042] A sensor 23 is attached to the high-voltage line 17 and measures the current flowing through the line 71. In the embodiment shown, the sensor 23 is a coil 31, which is induced by the current in the line 17. The induced current in the coil allows conclusions to be drawn about the current in the high-voltage line 17. Disturbances in the current through the high-voltage line 17 are detected by the induction coil 25. An alternative method for measuring the interference voltage in the high-voltage line 17 caused by arcing is to measure the voltage at the end of the high-voltage line 17, as shown in Figure 2. The high-voltage line 17 must be grounded in this embodiment. In this way, the grounded cable shield, together with the coupling capacitance between the high-voltage conductor 17 and the cable shield, forms an AC voltage divider. By measuring the voltage of the AC voltage divider, an interference voltage can be detected.At the end of the high-voltage line 17 are the usual operating equipment such as fuses, instrument transformers and transformer 15.

[0043] Figure 3 shows an arrangement in which a current transformer 27 with a high-pass filter is arranged as a sensor 25 between the high-voltage line 17 and, for example, the transformer 15. Using the high-pass filter, the voltage measurement range in the high-voltage line with low frequencies can be filtered and thus ignored. These filtered measured values ​​are not considered for evaluation and enable faster processing of the measured values. The interference voltage in the high-voltage line 17, which is detected by the devices shown in Figure 3, typically has a frequency above approximately 10 kHz.

[0044] Another arrangement is shown in Figure 4, in which an indirect current measurement is performed on the high-voltage line 17 by measuring the fluctuations in the magnetic field using a magnetic sensor 29. For this purpose, the fluctuations in the magnetic field must be detected. Since the disturbances in the magnetic field are caused by changes in the current, the current can be determined by measuring the fluctuations in the magnetic field. Thus, with the arrangement shown in Figure 4, an indirect current measurement is performed by the sensor 23.

[0045] Legend:

[0046] 11 High-voltage power transmission system

[0047] 13 Pantograph

[0048] 15 Transformer

[0049] 17 High-voltage line

[0050] 23 Sensor

[0051] 25 Induction coil

[0052] 27 current transformers

[0053] 29 Magnetic sensor

Claims

Patent claims 1. A method for detecting an arc at a sliding contact between a current-carrying conductor and a high-voltage power transmission system (11) designed to provide a transmission of electrical energy to a vehicle, wherein electrical energy is transmitted via a high-voltage conductor (17) of the high-voltage power transmission system (11), in particular at a current collector system of traffic installations such as a pantograph (13) on a locomotive, in which method either a) the change in the operating current through a conductor, in particular the high-voltage conductor (17), caused by an arc, or b) the change in the voltage at the cable shield of the conductor caused by an arc, or c) the time-varying magnetic field in the immediate vicinity of the conductor caused by an arc is analyzed and evaluated,so that the power supply of the power transmission system (11) can be switched off in good time to avoid further damage.

2. Method according to claim 1, wherein the high-voltage conductor (17) is at least partially provided with a cable shield, in particular wherein the cable shield of the high-voltage conductor (17) is connected to ground at one end and the voltage is tapped at the cable shield of the high-voltage conductor.

3. Method according to claim 1 to 2, wherein the magnetic field is detected at a short distance from the high-voltage conductor (17) by one or more magnetic field sensors or by a Rogowski coil.

4. Method according to one of claims 1 to 2, wherein the current is measured by a non-contact current sensor or a current transformer.

5. Method according to one of claims 1 to 4, wherein the measuring methods according to methods a), b) or c) generate a noise signal which is analyzed and evaluated.

6. Method according to one of claims 1 to 5, wherein the evaluation is based on at least two different measuring methods according to methods a), b) or c).

7. Method according to one of claims 1 to 6, wherein the evaluation is carried out by an electronic acquisition unit which samples the signals at at least 100 kHz after they have been suitably filtered in an analogue manner, in particular wherein the signals are mathematically processed and evaluated.

8. Method according to one of claims 1 to 7, wherein the evaluation is carried out by an electronic circuit which, after suitable filtering and subdivision into frequency bands, measures the energy content in the individual frequency bands and issues an alarm signal when an adjustable threshold value is exceeded.

9. Method according to one of claims 1 to 8, wherein the frequency range greater than 10 kHz of the measured current or the measured voltage is analyzed and evaluated.

10. Method according to one of claims 1 to 9, wherein the frequency range of the measured current or the measured voltage below 10 kHz is filtered, preferably by a high-pass filter.

11. Device for detecting an arc at a sliding contact between a current-carrying conductor and a high-voltage power transmission system (11) which is designed to provide a transmission of electrical energy to a vehicle, wherein current is transmitted via a high-voltage conductor (17) of the high-voltage power transmission system (11) which is at least partially provided with a cable shield, in particular at a current collector system of traffic installations such as a pantograph (13) on a locomotive, wherein the device has a measuring device either for measuring the change in the operating current through a conductor, in particular the high-voltage conductor (17), caused by an arc, for measuring the change in the Voltage at the cable shield of the conductor, or to measure the time-varying magnetic field caused by an arc in the immediate vicinity of the conductor.

12. Device according to claim 11, wherein the measuring device comprises a current sensor or a coil for voltage measurement, in particular a Rogowski coil.

13. Device according to claim 11 or 12, wherein the measuring device comprises a filter which filters a frequency range of the measurement.

14. The device of claim 13, wherein the filter is a high-pass filter which filters the frequency below 10 kHz.

15. Device according to one of claims 11 to 14, wherein the high-voltage conductor (17) is electrically grounded.

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