Device for generating and measuring an arc

Abstract

Device (1) for generating and measuring an arc (LB) which is ignited between electrodes (2, 3), wherein at least one of the electrodes (2, 3) has an electrode holder (2A, 3A) which is designed as a hollow shaft, in the center of which is provided a line (12) which is surrounded by an electrically insulating layer (13) and consists of an electrically conductive material, for measuring the electrical voltage applied to the electrode (2, 3), wherein the electrode holder (2A, 3A) designed as a hollow shaft has a hollow cylindrical electrically conductive jacket (14) which surrounds the electrically insulating layer (13) and is used to apply an electrical voltage to an electrode cap (2B, 3B) held by the electrode holder (2A, 3A).

Description

The invention relates to a device for generating and measuring an arc and to a corresponding method for measuring an arc using such a device.Arcs may be generated unintentionally in different applications, in particular in photovoltaic installations. Arcs can lead to system failures and damage equipment within a plant.Erhard, "Contribution to arcing fault detection in photovoltaic installations", University Verlag Ilmenitenau, 2017, is concerned with arcing fault detection. Ameen, et al., "Mechatronics Arc Generator for Photovoltaic Arc Fault Detector Testing", IEEE 46th Photovoltaic Specialists Conference (PVSC), Chicago, IL, USA, 2019, pp. 1306-1311, relates to an arc generator with arc fault detection. Zhao et al., "Series Arc Fault Diagnosis Based on Variational Mode Decomposition and Random Forest", in Frontiers in Energy Research, Vol. 10, June 2022, pp. 2-16 relates to improving fault arc detection.Different conditions or factors can increase the risk of an arc being generated within a system. Typically, defective photovoltaic modules or legacy electrical contacts may increase the risk of creating an arc. Further environmental factors or influencing parameters have an effect on the formation of an arc, for example air humidity, temperature or ambient air pressure. A further factor is the electrical voltage present within the installation or the electrical current flowing via components of the installation.It is therefore an object of the present invention to provide a device for generating and measuring an arc, which device makes it possible to generate arcs reproducibly as a function of different parameters and to obtain measurement data of the arc that is generated.This object is achieved according to the invention by a device having the features specified in patent claim 1.The invention accordingly provides a device for generating and measuring an arc which is ignited between electrodes, wherein at least one of the electrodes has an electrode holder which is designed as a hollow shaft in which a line which is surrounded by an electrically insulating layer and which consists of an electrically conductive material is provided in the middle for measuring the electrical voltage present at the electrode.The device according to the invention offers the advantage that the electrical voltage actually present at the electrode can be measured. This is possible due to the coaxial construction of the electrode holder of the relevant electrode. The device according to the invention thus allows a very accurate measurement of the ignited arc depending on the electric voltage present at the electrode.In the device according to the invention, the electrode holder designed as a hollow shaft has a hollow cylindrical electrically conductive jacket enclosing the electrically insulating layer for applying an electrical voltage to an electrode cap held by the electrode holder.In a further possible embodiment of the device according to the invention, the electrode cap is attached to an end face of the cylindrical electrode holder designed as a hollow shaft.In a further possible embodiment of the device according to the invention, the electrode holder of the electrode is rotatably mounted by at least one ball bearing.Alignment errors can thereby be compensated. Furthermore, the arc is ignited randomly at any of the points on the surface of the respective electrode cap, so that a randomisation of the geometric ignition points is achieved. The rotation ensures that in the next measurements it is not ignited again at the same crater point.In a further possible embodiment of the device according to the invention, the ball bearing has an electrically insulating ceramic ball bearing.This ceramic ball bearing offers reliable electrical insulation of the high electrical voltage present at the electrode.In a possible implementation of the device according to the invention, the electrically insulating ceramic ball bearing is made of zirconium oxide.In a further possible embodiment of the device according to the invention, the ball bearing is mechanically prestressed by means of a spring in the longitudinal direction of the rotatably mounted electrode holder.This mechanical prestress is helpful in particular when using a ceramic ball bearing made of zirconium oxide, since this cannot be manufactured as precisely as, for example, a ball bearing made of steel. Accordingly, ceramic ball bearings generally have a substantially higher unwanted axial play. Due to the spring-loaded prestress in the axial direction, the balls of the ball bearing are pressed onto the corresponding shoulders of the rings of the ball bearing, so that the axial play is significantly reduced as a result.By using a ceramic ball bearing with spring prestress, an insulated, smooth and very precise mounting of the electrodes is thus achieved.In a further possible embodiment of the device according to the invention, at least one electrode holder of an electrode of the device is arranged movably in the longitudinal direction of the electrode holder by means of a slide.This makes it possible to set a gap or a gap between the two electrode caps of the electrodes attached on the end face.In one possible implementation, the carriage is provided on two parallel-arranged carriage support shafts of the device. The carriage is preferably guided through the ball bearings, which in turn can run on hardened shafts.In a further possible embodiment of the device according to the invention, the two mutually opposite electrode caps of the two electrodes of the device are arranged in a transparent glass cylinder.This glass cylinder is preferably designed closed and has in its interior a defined adjustable atmosphere of an exchangeable gas or exchangeable gas mixture.The glass cylinder makes it possible to generate a defined atmosphere in which the arc to be measured is ignited via the two electrodes.In a possible embodiment of the device according to the invention, physical parameters of the atmosphere prevailing within the glass cylinder can be adjusted by a local control of the device or by a remote control of a plant.In a possible embodiment of the device according to the invention, the adjustable physical parameters of the atmosphere of the gas or gas mixture prevailing within the glass cylinder comprise a temperature, a physical pressure and a humidity of the gas or gas mixture.In a further possible embodiment of the device according to the invention, the gas or gas mixture located within the glass cylinder has a protective gas.In a further possible embodiment of the device according to the invention, at least one camera is provided in addition to the glass cylinder of the device, said camera recording the behavior of the arc ignited between the electrodes.In a further possible embodiment of the device according to the invention, the electrode caps of the electrodes for igniting the arc are moved away from one another in the longitudinal direction of the electrode holders by means of a controllable slide.In a further possible embodiment of the device according to the invention, the distance or the gap between the electrode caps of the electrodes can be adjusted exactly by controlling the device.In a further possible embodiment of the device according to the invention, the electrode cap of an electrode is interchangeably screwed into the end face of the cylindrical electrode holder of the respective electrode, which holder is designed as a hollow shaft.In a further possible embodiment of the device according to the invention, an electrically conductive plate is provided on the hollow cylindrical electrically conductive jacket of the electrode holder. Current is introduced via the conductive disk when the electrode is stationary.In a further possible embodiment of the device according to the invention, the rotatably mounted electrode holder of the electrode is rotated about its longitudinal axis, in particular after the arc has been measured, by an associated controllable stepping motor. A rotation of the electrodes thus advantageously does not take place during the measurement of the arc. However, the electrodes can be rotated between two successive measurements with an adjustable angle of rotation in order to strike the arc at another point of the electrode cap.This stepping motor can be controlled by a control of the device.In a further possible embodiment of the device according to the invention, after the arc has been ignited, an electric current flows between the electrode caps of the electrodes through the electrically conductive jacket of the electrode holder of the electrode.In a further possible embodiment of the device according to the invention, at least one cooling slot for cooling the relevant electrode by compressed cooling air is milled into the electrode holders of the electrodes.The surface of the electrode holder is enlarged by the milled-in cooling slots, so that better cooling can be achieved. Furthermore, the milled cooling slots increase a degree of turbulence of the surrounding cooling air, in order to thereby facilitate the removal of heat.In a further possible embodiment of the device according to the invention, the centrally arranged line of the electrode holder, which is formed as a hollow shaft and is surrounded by an electrically insulating layer and is made of an electrically conductive material, is connected to a voltage measuring unit for measuring the electrical voltage present at the electrode.In a further possible embodiment of the device according to the invention, a current measuring unit for measuring the electric current flowing via the ignited arc is provided on one of the electrodes.In a further possible embodiment of the device according to the invention, the device has different measuring units for measuring parameters of the ignited arc, which can be evaluated by a data processing unit of the device.These measuring units comprise in particular a voltage measuring unit for measuring the electrical voltage present at the electrode, a current measuring unit for measuring the electrical current flowing via the arc, and a camera for recording the arc within the glass cylinder and sensors for detecting physical parameters of the atmosphere of the gas mixture or gas prevailing within the glass cylinder.The various measuring units, cameras and sensors supply data which can be evaluated by a data processing unit of the device.The data processing unit may be connected to a controller of the apparatus.In a possible embodiment of the device according to the invention, the electrical voltage applied to a first electrode of the device is generated by a controllable voltage generator of the device.In a further possible embodiment of the device according to the invention, the electric current flowing via the ignited arc flows away to a controllable and / or replaceable load which can be connected to a second electrode of the device.In a further possible embodiment of the device according to the invention, the controllable voltage generator and / or the controllable load for measuring the arc ignited between the electrodes are controlled by a local control of the device or by a remote control of a system.In a further possible embodiment of the device according to the invention, the measurement data transmitted to the data processing unit of the controller are stored in a local data memory or in a cloud for evaluating the measurement data.In a further possible embodiment of the device according to the invention, by applying the electrical voltage generated by the voltage generator or by applying an electrical voltage profile to the electrodes, an arc which occurs during faulty operation of a system, in particular a photovoltaic system, can be generated.In a further possible embodiment of the device according to the invention, the electrode cap, which is attached to an end face of an electrode holder, has a rotationally symmetrical shape. In one possible implementation, the electrode cap has a semi-circular shape, a parabolic shape or a conical shape.According to a further aspect, the invention also provides a method for measuring an arc having the features specified in patent claim 23.The invention accordingly provides a method for measuring an arc with a device according to the invention, having the steps:applying an electrical voltage to a first electrode of the device,moving a second electrode of the device longitudinally relative to the first electrode of the device until an electric arc is struck across a gap created between the two electrodes; andevaluating measurement data for measuring the ignited arc.In a further possible embodiment of the method according to the invention, the size of the gap formed between the electrodes is adjusted with a high accuracy of a few micrometers.Possible embodiments of the device according to the invention and of the method according to the invention for generating and measuring an arc are explained in more detail below with reference to the appended figures.The following are shown: FIG. 1 shows a view obliquely from above of a possible embodiment of a device according to the invention for generating and measuring an arc; FIG. 2 is an oblique view of a first electrode of the device shown in FIG. 1; FIG. 3 is a first sectional view of the electrode shown in FIG. 2 supported by a carriage; FIG. 4 is a further sectional view through the first electrode of the device shown in FIG. 2, which is held by a carriage; FIG. 5 is a further sectional view through the first electrode of the device shown in FIG. 2, which is supported by a carriage; FIG. 6 shows a schematic illustration of a possible test arrangement for generating and measuring an arc with the aid of the device according to the invention; FIG. 7 shows a flow diagram of a possible embodiment of the method according to the invention for generating and measuring an arc.FIG. 1 shows a view obliquely from above of a possible embodiment of a device 1 according to the invention for generating and measuring an arc LB. The arc LB is ignited between two electrodes 2, 3. To generate the arc LB, after application of a voltage, the two electrodes 2, 3 are moved apart in the longitudinal direction in order to generate a gap S.In FIG. 1, a first electrode 2 and an opposite second electrode 3 are seen, which are separated from one another by a narrow gap S. The two electrodes 2, 3 are located in a chamber or a glass cylinder 4. The corresponding electrode holder 2A has in the middle a line which is surrounded by an electrically insulating layer and which consists of an electrically conductive material. This centrally arranged electrically conductive line serves for the exact measurement of the electrical voltage U present at the relevant electrode 2, 3.In the exemplary embodiment shown in FIG. 1, the first electrode 2 of the device 1 is arranged movably with the aid of a carriage 5. The support of the electrode 2 by the movable slide 5 makes it possible to move the electrode 2 longitudinally relative to the second electrode 3 to create a gap S between the electrodes 2, 3. The size of the gap S formed between the electrodes 2, 3 can be adjusted with the aid of the carriage 5 with a high accuracy of a few micrometers.In the embodiment shown in FIG. 1, the first electrode 2 has an electrode holder 2A which is designed as a hollow shaft. This hollow shaft comprises in its center an electrical line consisting of an electrically conductive material or a conductive cylindrical core 12 for measuring the electrical voltage U present at the electrode 2 This centrally arranged measurement line 12 is surrounded by an electrically insulating layer 13 which forms a hollow cylindrical electrically non-conductive insulating jacket which is in turn surrounded by an electrically conductive jacket 14, as can also be seen in FIGS. 3, 4, 5.This enclosing, hollow cylindrical, electrically conductive jacket 14 serves for applying an electrical voltage U to an electrode cap 2B of the electrode 2 held by the electrode holder 2A of the electrode 2. The electrode holder 2A of the electrode 2 of the device 1 is preferably rotatably mounted by at least one ball bearing. The electrode holder 2A of the first electrode 2 of the apparatus 1 is arranged to be movable in the longitudinal direction by means of the carriage 5. In the embodiment shown in FIG. 1, the carriage 5 runs on two parallel-aligned carriage support shafts 6A, 6B.The two mutually opposite electrode caps 2B, 3B of the two electrodes 2, 3 of the device 1 are arranged in the transparent glass cylinder 4. This glass cylinder 4 is of closed design and has in its interior a defined atmosphere of a gas or of an exchangeable gas mixture.Physical parameters of the atmosphere prevailing within the glass cylinder 4 can be adjusted by a local control of the apparatus 1 or by a remote control of a plant. These adjustable physical parameters of the atmosphere of the gas or of the gas mixture prevailing within the glass cylinder 4 comprise, for example, a temperature T, a pressure p and a humidity η of the gas or gas mixture. In one possible embodiment, the gas or gas mixture located within the glass cylinder 4 comprises a protective gas.The electrode caps of the electrodes 2, 3 within the glass cylinder 4 are moved away from one another by means of the controllable slide 5 in the longitudinal direction of the associated electrode holders of the electrodes 2, 3 in order to strike the arc LB to be measured, in order to create a gap S. The distance between the electrode caps of the electrodes 2, 3 or the size of the gap S can be adjusted with high accuracy by a control of the device 1 in a possible embodiment.The movable carriage 5 shown in FIG. 1 can be guided by linear ball bearings. These linear ball bearings in turn ride on the hardened shafts 6A, 6B serving as carriage support shafts. The carriage support shafts 6A, 6B are supported by two opposed posts 7, 8 mounted on a base plate 9. The base plate 9 and the two posts 7, 8 or changes in setup are preferably made of tool steel in order to ensure maximum stability and torsional rigidity. All the components are mechanically connected to one another by means of dowel pins. This allows, for example, when replacing components, to be able to restore an exact position.In one possible embodiment, a stage is located below the carriage 5, with which stage the position of the carriage 5 can be approached exactly to micrometers. This position can be measured, for example, with the aid of a glass scale.On the upper side of the slide 5 there are electrical connection contacts 10 for an electrical current line for distributing the electrical current I to various sliding contacts or sliding pins which bear against an electrically conductive disc 15 of the electrode holder 2A of the first electrode 2. The electrodes 2, 3 do not rotate when the arc LB is ignited. During the measurement (i.e. ignition and holding of the arc LB), the electrodes 2, 3 are stationary with respect to rotation; only a movement in the longitudinal direction takes place. The rotation of the electrodes 2, 3 serves to ensure that, after rotating at least one electrode 2, 3, no re-ignition occurs at the same points of the electrodes 2, 3 when an arc LB is measured again. The electrodes 2, 3 can be rotated with an adjustable angle of rotation between the measurements.After the arc LB has been ignited, an electric current I flows between the electrode caps 2B, 3B of the two electrodes 2, 3 via the respective electrically conductive jacket 14 of the electrode holders 2A, 3A of the two electrodes 2, 3. The current I flowing via the jacket 14 of the second electrode 3 can in turn be tapped via a disk by means of sliding contacts and can be fed via electric contacts 11 to a current measuring unit 20 of the device 1 for measuring the electric current I flowing via the arc LB.In the exemplary embodiment shown in FIG. 1, the current can be introduced by bronze carbon sliding contacts. The stress measurement is preferably carried out on vertically mounted contact pins directly in front of a hexagonal drive. This allows a measurement with the correct current and voltage. The hexagonal drive serves as an interface for rotating the electrodes 2, 3, for example by an associated stepping motor.A high electrical voltage of up to 1000 volts DC can be present between the two electrodes 2, 3. Due to this high electrical voltage, ceramic ball bearings, in particular made of zirconium oxide, are preferably used in order to ensure adequate electrical insulation. In one possible embodiment, the electrically insulating ceramic ball bearings 16, 17 can be mechanically prestressed in the longitudinal direction by at least one spring 18, as is also shown in FIGS. 4, 5. Preferably, three springs 18 are provided offset by 120 degrees on the circumference. The spring-loaded axial prestress makes the ball bearings free of play, so that misalignment errors are compensated. Due to the spring-loaded mechanical prestress in the longitudinal direction of the electrodes 2, 3, the balls of the ball bearing 16, 17 are pressed onto the shoulders of the rings of the ball bearing, whereby the mechanical play is minimized. The ceramic ball bearings thus offer an insulated, smooth and precise bearing of the electrodes 2, 3.FIG. 2 shows an oblique view of the first electrode 2 within the device 1 according to the invention, as is shown in FIG. 1. The electrode 2 includes an electrode holder 2A and an electrode cap 2B. The electrode holder 2A and the electrode cap 2B fixed thereto are movably disposed on parallel-aligned carriage support shafts 6A, 6B by the carriage 5. The electrode cap 2B of the electrode 2 is preferably interchangeably attached to an end face of the electrode holder 2A. In one possible implementation, the electrode cap 2B is interchangeably screwed to the end face of the cylindrical electrode holder 2A of the electrode 2, which holder is designed as a hollow shaft.In the exemplary embodiment shown, the electrode holder 2A of the electrode 2 is designed as a hollow shaft, as can be seen from the sectional views according to FIGS. 3, 4, 5. As shown in FIG. 3, the electrode holder 2A has an electrically conductive core 12 centrally along its longitudinal axis, which core is surrounded by an electrically insulating layer 13. The electrically conductive core 12 extends as far as the end face of the electrode holder 2A and allows the electrical voltage U applied to the electrode cap 2B of the electrode 2 to be tapped and measured as an electrical line.The electrode holder 2A, which is designed as a hollow shaft, has a hollow cylindrical electrically conductive jacket 14 enclosing the electrically insulating layer 13. This electrically conductive jacket 14 serves for applying an electric current I to the electrode cap 2B held by the electrode holder 2A, whereby a voltage is set. As can be seen in FIG. 3, the electrode cap 2B is attached to the front end side of the cylindrical electrode holder 2A, which is designed as a hollow shaft.In the embodiment shown in FIGS. 2 to 5, the electrode cap 2B is formed in a hemispherical shape. The electrode cap 2B can be screwed into the end face of the electrode holder 2A with a screw. In one possible embodiment, the electrode cap 2B may be replaced. The electrode cap 2B preferably has a rotationally symmetrical shape. For example, the electrode cap 2B may be formed hemispherically, as shown in FIGS. 2 to 5, or may have other rotationally symmetrical shapes, such as a parabolic shape or a conical shape. Both the core 12 and the jacket 14 consist of an electrically conductive material or of an electrically conductive material alloy, for example brass.On the hollow cylindrical electrically conductive jacket 14 of the electrode holder 2A, as can be seen in FIG. 3, an electrically conductive plate 15 is provided. The electrical voltage U applied to the first electrode 2 can be generated, for example, by a controllable voltage generator of the device 1. The voltage U generated by the voltage generator is applied via the sliding contacts to the hollow cylindrical electrically conductive jacket 14, which is connected to the electrode cap 2B.After the arc LB has been ignited, an electric current I flows via the electrode cap 2B of the first electrode 2 to the electrode cap 3B of the opposite second electrode 3. This current I flows via the electrically conductive disk 15 and the hollow cylindrical electrically conductive jacket 14 to the electrode cap 2B of the first electrode 2 and from there via the arc LB ignited in the gap S to the electrode cap 3B of the opposite second electrode 3.At least one of the two electrodes 2, 3 has an electrode holder which is designed as a hollow shaft. For example, the electrode 2 can have a measurement line 12 which is arranged centrally and is surrounded by the electrically insulating layer 13 and serves for measuring the electrical voltage U present at the electrode cap 2B.In conventional measuring devices, the voltage directly applied to the electrode cannot be measured. In conventional devices, the voltage at the leads of the electrodes 2, 3 is measured. With the device 1 according to the invention, it is thus possible to determine exactly the voltage U actually applied to the caps of the two electrodes 2, 3 when the arc LB is ignited. Preferably, both electrode holders 2A, 3A of the two electrodes 2, 3 are designed as hollow shafts. In the hollow shaft there is centrally located the return line for the voltage measurement of the applied voltage. After the arc LB has been ignited, the current flows via the outer ring or jacket 14 of the electrode holder 2A. The voltage U is measured via the centrally located electrically conductive core 12 of the hollow shaft.In the sectional view of FIG. 3, two cut ball bearing rings 16, 17 for rotatably mounting the electrode holder 2A can be seen. Since a high electric voltage U is applied to the jacket 14 of the electrode holder 2A for igniting the arc LB, the ball bearings 16, 17 are preferably made of an electrically insulating ceramic material. Preferably, the electrically insulating ceramic ball bearings 16, 17 consist of zirconium oxide.The carriage 5 has cylindrical fitting holes 18A, 18B and runs on hardened shafts 6A, 6B, as can be seen in FIG. 1.FIG. 4 shows a further sectional view through the first electrode 2 of the device 1. the electrode 2 comprises the electrode holder 2A and the electrode cap 2B attached thereto. The ball bearings 16, 17 are mechanically biased in the longitudinal direction of the rotatably supported electrode holder 2A by a spring 18, as shown in FIG. 4. By means of the mechanical prestress, a mechanical play of the ceramic ball bearings 16, 17 can be minimized.Cooling slots 19 can also be seen in FIG. 4, which are milled into the electrode holder 2A and are provided for cooling the electrode 2 by means of compressed cooling air, for example. The cooling of the electrode holder 2A of the electrode 2 allows a higher measurement frequency.FIG. 5 shows a further sectional view through the first electrode 2, which can be moved in the longitudinal direction by a carriage 5. The electrode 2 is designed as a hollow shaft.FIG. 6 schematically shows a device 1 for generating and measuring an arc LB. The device 1 has two electrodes 2, 3, each of which is designed as a hollow shaft. This allows direct direct measurement of the electrical voltages U present at the two electrode caps 2B, 3B of the electrodes 2, 3 by a voltage measurement unit 26, as is illustrated in FIG. 6. The voltage measurement unit 26 may measure the voltage U 1 applied to the first electrode 2 and the voltage U 2 applied to the second electrode 3. The voltage difference or potential difference produces the electrical voltage U applied via the ignited arc LB. A current measuring unit 20 serves for measuring the electrical current I flowing via the arc LB. A camera 21 is provided next to the glass cylinder 4. The camera 21 serves to record the behavior of the arc LB within the glass cylinder 4. In possible embodiments, sensors are also provided for detecting parameters of the atmosphere of the gas mixture or gas prevailing within the glass cylinder 4. These physical parameters comprise, for example, a temperature T, a pressure p or a humidity of the gas or gas mixture inside the glass cylinder 4. The device 1 has a controller 22 with a data processing unit or a processor integrated therein. The measurement data supplied by the various measuring units are evaluated by the data processing unit of the controller 22 of the apparatus 1. In addition, the data processing unit can also evaluate a camera image KB supplied by the camera 21 during the measurement of the arc LB.The controller 22 generates control signals CTRL for controlling various components of the device 1. in the exemplary embodiment illustrated in FIG. 6, a current or voltage generator 23 is provided, which applies an electrical voltage U to the first electrode 2 of the device 1. This electrical voltage U can be generated by the controllable voltage or current generator 23. The electric current I flowing via the ignited arc LB flows off to a controllable or replaceable load which can be connected to the second electrode 3 of the device 1.In the example shown in FIG. 6, the load is an inverter 24 receiving the electric current I from the second electrode 3 of the device 1. The controllable voltage generator 23 and the controllable load for measuring the arc LB ignited between the electrodes 2, 3 can be controlled by the local controller 22 of the apparatus 1 during the measurement process. In one possible embodiment, the measurement data transmitted from the measuring units to the data processing unit of the controller 22 can be stored in a local data memory or via a data interface in a data cloud for further evaluation. In one possible embodiment, the apparatus 1 can also be connected to individual photovoltaic modules 25 of a photovoltaic installation in order to measure their behavior.As can be seen in FIG. 6, the controller 22 receives various measurement data, namely the electrical voltages U1 Mess, U2 Mess which are present at the electrode caps 2B, 3B of the two electrodes 2, 3 of the apparatus 1, and current measurement data I Mess of the electrical current I flowing via the arc LB. In addition, the controller 22 receives measurement data from the various sensors provided on the glass cylinder 4, i.e. measurement data of various physical parameters, in particular the pressure p prevailing within the glass cylinder 4, the temperature T of the gas contained within the glass cylinder 4 and the humidity of the gas mixture prevailing within the glass cylinder 4.The controller 22 can actuate various actuators during the measurement of the arc LB, in particular the carriage 5 for moving the first electrode 2 relative to the second electrode 3 in the longitudinal direction. Furthermore, for example, the supply of compressed air for cooling the electrodes 2, 3 can be controlled by the controller 22 during the measurement of the arc LB. Furthermore, the controller 22 can switch between the controllable voltage generator 23 and a component to be measured, for example the photovoltaic module 25 illustrated in FIG. 6.Furthermore, during the measurement of the arc LB, the controller 22 can control the operating behavior of a connected load, for example an inverter 24, in order to simulate different operating situations of the installation. The behavior of the arc LB within the glass cylinder 4 can be recorded by means of the camera 21 during the measurement.FIG. 7 shows a simple flow diagram for illustrating an exemplary embodiment of the method according to the invention for measuring an arc LB. The measurement of the arc LB is preferably carried out with a device 1 according to the invention.In a first step S 1, an electrical voltage is applied to the first electrode 2 of the device 1.In a further step S 2, a second electrode 2 of the device 1 is moved away in the longitudinal direction relative to the first electrode 2 of the device 1 until the electric arc LB is ignited via a gap S formed between the two electrodes 2, 3.Subsequently, in a step S 3, measurement data for measuring the ignited arc LB are evaluated.The evaluation can be carried out by a data processing unit contained in the controller 22. For simulating different operating scenarios, the controller 22 can actuate different components during the measurement, in particular the voltage generator 23 and the load 24. For example, by controlling the carriage 5, the width of the gap S formed can be changed.Furthermore, actuators for setting the physical parameters of the gas mixture located within the glass cylinder 4 can be controlled by the controller 22. For example, a heating device for heating the gas mixture provided inside the glass cylinder 4 can be provided as an actuator. Furthermore, an actuator for setting the relative air humidity of the air-gas mixture located within the glass cylinder 4 can be provided. The pressure p of the gas mixture located within the glass cylinder 4 can also be adjusted by the controller 22 during the measurement of the arc LB. The device 1 according to the invention thus allows reproducible generation and flexible and extremely precise measurement of an arc LB under a wide variety of operating conditions.For measuring the arc, a processor of the controller 22 can execute a measurement program, loaded from a database, for igniting and measuring an arc LB, which delivers measurement data for examining specific plant configurations of a plant under various operating conditions.

Claims

Device (1) for generating and measuring an arc (LB) which is ignited between electrodes (2, 3), wherein at least one of the electrodes (2, 3) has an electrode holder (2A, 3A) which is designed as a hollow shaft in which a line (12) which is surrounded by an electrically insulating layer (13) and consists of an electrically conductive material is provided in the middle for measuring the electrical voltage present at the electrode (2, 3), wherein the electrode holder (2A, 3A) designed as a hollow shaft has an electrically conductive jacket (14), which surrounds the electrically insulating layer (13), in the form of a hollow cylinder for applying an electrical voltage to an electrode cap (2B, 3B) held by the electrode holder (2A, 3A).Device (1) according to claim 1, wherein the electrode cap (2B, 3B) is attached to an end face of the cylindrical electrode holder (2A, 3A) configured as a hollow shaft.Device (1) according to claim 1 or 2, wherein the electrode holder (2A, 3A) of the electrode (2, 3) is rotatably supported by at least one electrically insulating ceramic ball bearing (16, 17).Device (1) according to claim 3, wherein the ball bearing (16, 17) is mechanically prestressed in the longitudinal direction of the rotatably mounted electrode holder (2A, 3A) by means of at least one spring (18).Device (1) according to any one of the preceding claims 1 to 4, wherein at least one electrode support (2A, 3A) of the electrodes (2, 3) of the device is arranged movably in the longitudinal direction of the electrode support (2A, 3A) by means of a carriage (5) running on two parallel aligned carriage support shafts (6A, 6B) of the device.Device (1) according to one of the preceding claims 1 to 5, wherein the two mutually opposite electrode caps (2B, 3B) of the two electrodes (2, 3) of the device are arranged in a transparent glass cylinder (4), wherein the glass cylinder (4) is formed closed and has in its interior a defined atmosphere of a replaceable gas or replaceable gas mixture, wherein the adjustable physical parameters of the atmosphere of the gas or gas mixture prevailing within the glass cylinder (4) comprise a temperature, T, a pressure, p, and a humidity of the gas or gas mixture.The device (1) according to claim 6, wherein physical parameters of the atmosphere prevailing inside the glass cylinder (4) are adjustable by a local controller (22) of the device (1) or by a remote controller of a plant.Device (1) according to either of Claims 6 and 7, wherein, in addition to the glass cylinder (4), at least one camera (21) is provided which records the behavior of the arc (LB) ignited between the electrodes (2, 3).Device (1) according to one of Claims 6 to 8, wherein the electrode caps (2B, 3B) of the electrodes (2, 3) for igniting the arc (LB) are moved away from one another in the longitudinal direction of the electrode holders (2A, 3A) by means of a controllable slide (5).The device (1) according to claim 9, wherein the distance between the electrode caps (2B, 3B) of the electrodes (2, 3) is controllable by a controller (22).Device (1) according to one of the preceding claims 1 to 10, wherein the electrode cap (2B, 3B) of an electrode (2, 3) is interchangeably screwed into the end face of the cylindrical electrode holder (2A, 3A) of the respective electrode (2, 3) designed as a hollow shaft.Device (1) according to one of the preceding claims 3 to 11, wherein the rotatably mounted electrode holder (2A, 3A) of the electrode (2, 3) is rotated about its longitudinal axis after the arc has been measured by a controllable stepping motor belonging to the same.Device (1) according to one of Claims 1 to 12, wherein, after the arc (LB) has been ignited, an electrical current, I, flows between the electrode caps (2B, 3B) of the electrodes (2, 3) through the electrically conductive jacket (14) of the electrode holder (2A, 3A) of the electrode (2, 3).Device (1) according to one of the preceding claims 1 to 13, wherein in each case at least one cooling slot (19) for cooling the electrode (2, 3) by compressed cooling air is milled into the electrode holders (2A, 3A) of the electrodes (2, 3).The device (1) according to any one of the preceding claims 1 to 14, wherein an electroless voltage on an electrode cap (2B, 3B) is measured by a voltage measurement unit (26).Device (1) according to one of the preceding claims 1 to 15, wherein a current measuring unit (20) for measuring the electric current flowing via the ignited arc (LB) is provided on one of the electrodes (2, 3).Device (1) according to one of the preceding claims 1 to 16, wherein the voltage measuring unit (26) for measuring the electrical voltage present at the electrode (2, 3), the current measuring unit (20) for measuring the electrical current flowing via the arc (LB), the camera (21) for recording the arc (LB) within the glass cylinder (4) and sensors for detecting parameters of the atmosphere of the gas mixture or gas prevailing within the glass cylinder (4) are connected to a data processing unit of a controller (22) of the device (1) for evaluating measurement data.The device (1) according to any one of the preceding claims 1 to 17, wherein the electrical voltage, U, applied to a first electrode (2) of the device (1) is generated by a controllable voltage generator (23) of the device (1).Device (1) according to one of the preceding claims 1 to 18, wherein the electric current, I, flowing via the ignited arc (LB) flows off to a controllable and / or replaceable load (24), which can be connected to a second electrode (3) of the device (1).The device (1) according to claim 19, wherein the controllable voltage generator (23) and / or the controllable load (24) for measuring the arc (LB) struck between the electrodes (2, 3) are controlled by a local controller (22) of the device (1) or by a remote controller of a plant.Device (1) according to one of the preceding claims 17 to 20, wherein the measurement data transmitted to the data processing unit of the controller (22) is stored in a local data memory or in a cloud for evaluation.Device (1) according to one of the preceding claims 1 to 21, wherein the electrode cap (2B, 3B) which is attached to an end face of an electrode holder (2A, 3A) has a rotationally symmetrical shape, in particular a semicircular shape, a parabolic shape or a conical shape.Method for measuring an arc with a device (1) according to one of Claims 1 to 22, having the steps: applying (S1) an electrical voltage to a first electrode (2) of the device; moving (S2) a second electrode (3) of the device in the longitudinal direction relative to the first electrode (2) of the device as far as an electric arc (LB) is ignited via a gap which forms between the two electrodes (2, 3); and evaluating (S3) measurement data for measuring the ignited arc (LB).Method according to claim 23, wherein the size of the gap (S) formed between the electrodes (2, 3) is adjusted with a high accuracy of a few micrometers.

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