SYSTEM FOR MONITORING A POWER LINE OF AN ELECTRIC MACHINE FED BY A FREQUENCY CONVERTER

Description

Object

[0001] Disclosed here is a system for monitoring a supply line of an electrical machine powered by a frequency converter. This monitoring system is implemented as a device and a method. Features and properties of the device and method are defined in the claims; however, the description and figures also disclose characteristics of the device and method, as well as their various aspects and interrelationships. background

[0002] Efficient maintenance is becoming increasingly important for maintaining the operation of electrically operated systems and machines. For electrical cables and lines, the two main approaches to maintenance are reactive maintenance, i.e., replacing cables / lines or connectors, etc., in the event of damage, and preventive maintenance. Preventive maintenance involves performing maintenance measures and replacing wear parts at predetermined intervals. Predictive maintenance involves collecting and evaluating key data from systems and machines during ongoing operation. To optimize costs and operational reliability, maintenance must be performed neither too early (resulting in high costs) nor too late (resulting in system and machine failure).

[0003] In industrial electrical systems and machines, cables are sometimes subject to extremely strong environmental influences. In moving and positively guided applications, e.g., in a power chain, cables are exposed to considerable bending and flexing loads. In robotic applications, torsional forces also apply. These cables include the supply cables for frequency converter-fed electrical machines discussed here. Even if the cables are specifically designed for this type of load, they are still considered wearing parts. Typical faults in such cables include wire breakage, sheath or insulation damage, geometric displacement in the cable structure, and damage to shielding elements. These faults lead to the supply of operating power to the load (the electrical machine) being reduced or even interrupted.Such unplanned degradations or failures due to external influences are usually costly, as they can lead to downtimes in industrial machinery and equipment, etc., with corresponding operational / production losses or even damage to the machinery and equipment. State of the art

[0004] In DE 1 038 140, a core of a cable with absorbent insulation material is surrounded by an impregnating substance, in this case paraffin. When the temperature changes, the dielectric constant changes. This allows the temperature and fault location to be determined by measuring the propagation time against a reference conductor. This requires a cable design that differs significantly from current cables, which also poses significant challenges for certification (e.g., fire safety). The arrangement described here has an evaluation device installed at both cable ends.

[0005] A time-domain reflectometer (TDR) is a device used to analyze an electrical line for impedance changes in order to identify associated anomalies based on those impedance changes. A TDR injects a pulse of electrical energy into an electrical line. When the electrical pulse encounters an impedance change along the length of the electrical line, a portion of the pulse's energy is reflected back to the time-domain reflectometer. By evaluating, for example, the amplitude and polarity of the reflected wave, a measure of the impedance change can be determined. In addition, by measuring the pulse's travel time, the location of the impedance change can also be determined. Typical anomalies that can cause an impedance change include, but are not limited to, splices, damage, neutral corrosion, broken conductors, etc.

[0006] US patent application No. 12 / 820886 "Online Time Domain Reflectometer System" relates to an in-situ time domain reflectometer that can be operated without taking the electrical line out of service.

[0007] For connection or control cables, two approaches have essentially been established: First, a measurement with an additional sensor element in the cable, in the form of an expanded wire that breaks in the event of overload, or a temperature / humidity sensor (see also DE 20 2017 102 410 U1, DE 10 2013 227 051 B4, DE 10 2018 204 171 A1). Second, the wires are disconnected during system downtimes and semi-automated measurement of resistance, TDR, capacitance, and breakdown voltage strength (see also EP 3 199 960 A1).

[0008] DE 10 2020 111 743 A1 relates to an integrated circuit and a method for monitoring a switching transistor and a motor system. For this purpose, a monitoring circuit is used, which is arranged on a monolithic integrated circuit and monitors an output signal of a first switching transistor for a first output edge transition at a monitoring terminal. A time measuring circuit on the integrated circuit serves to measure a first time delay between a first input edge transition of a first control signal and the first output edge transition. The first control signal is configured to cause a state change of the first switching transistor.An analysis circuit arranged on the integrated circuit serves to compare the measured first time delay with a first predetermined threshold value to form a first comparison result and to indicate a first error condition based on the first comparison result.

[0009] Document DE 11 2016 006 497 T5 discloses an electronic converter comprising controllable switches and a control system for operating the controllable switches. The control system is configured to control the controllable switches to generate at least one test voltage pulse. The electronic converter comprises a voltage sensor for detecting a reflected voltage caused by a reflection of the test voltage pulse in an electrical system connected to the electronic converter. The control system is configured to control the operation of the electronic converter at least partially according to information based on the detection of the reflected voltage. The information can be used, for example, to determine impermissible voltage pulse lengths that would cause reflection-based overvoltages and / or to detect faults such as short circuits and ground faults.

[0010] DE 101 12 844 A1, US 6,657,437 B1, EP 2 157 438 A1, DE 10 2010 000249 A1, DE 10 2005 055429 A1, DE 10 2018 204 173 A1, DE 10 2018 204 171 A1, DE 10 2018 204 177 A1, and DE 10 2018 204 174 A1 concern further technological background.

[0011] Especially for motor connection / servo cables, frequency converter manufacturers often specify capacitance-optimized and symmetrical cables for installation and operation of the respective machines. This is intended to limit the propagation of common-mode currents / interference to protective conductors and equipotential bonding lines resulting from frequency converter operation. Therefore, altering the cable structure, for example, to insert sacrificial wires or sensors into the cable, is undesirable / impossible with these cable types.

[0012] What is needed is a cost-effective, universal solution that is capable of continuously monitoring motor connection / servo cables during operation without the need for additional sensor elements, thus ensuring high system availability. Technical problem

[0013] Based on this, a robust, efficient and accurate investigation and evaluation and output of the failure probability of moving feeder lines of frequency converter-fed electrical machines is to be provided. Proposed solution

[0014] To solve this problem, devices or methods having the features or steps of the independent claims are proposed.

[0015] A device for monitoring a supply line of a frequency converter-fed electrical machine is used to detect failure, wear and / or aging of the electrical

[0016] supply line. The electrical supply line is designed and laid to connect an electrical machine in an industrial machine or system or in a land or aircraft to a frequency converter. The frequency converter is designed and intended to supply the electrical machine with a single-phase or multi-phase alternating voltage with preferably variable voltage amplitude and rotating field frequency via the electrical supply line, wherein a change in pulse duration / modulation depth and / or voltage amplitude of the alternating voltage serves to change a speed or torque of the electrical machine. The frequency converter is designed and intended to provide each phase of the alternating voltage as a sequence of rectangular pulses with a high edge steepness to supply the electrical machine.A detection and evaluation device is configured and programmed to detect and process a voltage signal profile on at least one or between at least two wires of the electrical supply line in order to obtain from the voltage signal profile a measure of the probability of occurrence of a failure, wear and / or aging of the line, and to output the obtained measure at an output.

[0017] "Electrical machines" here refer to internally or externally rotating motors and generators. Machines operated in alternating motor-generator mode are also included. It is also irrelevant whether such an electrical machine is designed as a rotary machine or a linear machine. In particular, this refers to electrical machines that operate as synchronous or asynchronous machines and that are powered by frequency converters with variable speeds. In addition to the speed (rpm), the torque or supply current of the electrical machine can also be varied if the frequency converter control system is designed accordingly. In the case of linear motors or stepper motors, precise angular positions can be reached by varying the pulse controls.

[0018] Using such a device and a method described below, line and cable diagnostics can be performed in systems and machines. The device and method are particularly suitable for connection / control or servo lines used in industrial machines and systems or in land, sea, or aircraft. All of these different metallically conductive (copper) lines and cables with one or more cores, core pairs (of the same or different cross-section), individual or collective shielding, insulating layers, and / or sheaths, in contrast to fiber optic cables, are referred to here as "electrical line," "feed line," or "line." Such a feed line is designed for a single-phase electrical machine as a two-wire system consisting of a line with an essentially constant cross-section and a ground line.It should be understood here that the pulse duration of the control pulses from the frequency converter is large compared to the transverse dimension of the cable. In a longitudinally homogeneous two-wire cable (with a constant cross-section), the voltage pulse propagates as a pure transverse wave in the direction of the longitudinal dimension of the cable. The same applies to a multi-phase electrical machine. For example, a three-phase machine (e.g., in a delta connection) is powered by a three-wire cable and a ground connection. In a three-wire system, an outer conductor, a neutral conductor, a protective earth, and, if necessary, a braided shield are provided. A neutral conductor is not required for star / delta operation.

[0019] Since the supply line between the frequency converter and the electrical machine has a finite length and is not open at the end - this is where the electrical machine is connected - reflections and pulses superimposed by the reflections occur whenever the line impedance is matched to the machine winding impedance of the voltage pulses from the frequency converter. Only if the line is terminated with its characteristic impedance on the machine side is the line reflection-free there. In all other cases (including open-circuit and short-circuit), reflections occur. Because the line is terminated, which is usually not matched to the characteristic impedance of the line, reflections occur at the line end. The ratio of the amplitude of the returning pulses to the amplitude of the incoming pulses is called the reflection factor.For a new / ideal feeder line, the reflection coefficient is the same at any point along its length, since the characteristic impedance is homogeneous along the ideal line. For this purpose, the reflection coefficient is considered at the respective distance from the machine. The reflection coefficient at a point along the length of the line is defined by the ratio of the amplitudes of the returning voltage wave to the forward voltage wave at that point.

[0020] A real feeder line has an inductance per unit length for AC or pulsed voltage operation and, due to ohmic components, a series resistance per unit length. In addition, a real feeder line also has a (transverse) capacitance per unit length with a conductance per unit length in the dielectric. These four factors primarily define the complex resistance of the line. Due to external influences, the complex resistance of the line can change locally along its length.

[0021] The reflection profile of the line is determined from the reflection factor present along the length of the line and non-linearly changing due to degradation. This reflection profile, resulting from the recorded voltage signal profile, is determined by the detection and evaluation device.

[0022] The frequency converter supplies the electrical machine (synchronous or asynchronous machine) with power at a variable speed depending on the load. To do this, the frequency converter converts the steady AC mains voltage (e.g., 380 volts, 50 hertz) into a pulsed AC voltage with variable amplitude and pulse duration. By controlling the pulse duration and voltage, continuous control of the speed or torque of the electrical machine is possible. The frequency converter has a rectifier bridge circuit on the input side.

[0023] This rectifier bridge circuit converts the incoming AC mains voltage (e.g. one or more, e.g. three phases) into a pulsating DC voltage. This pulsating DC voltage is smoothed in a DC circuit known as the intermediate circuit by a buffer capacitor and, if necessary, an inductance.

[0024] A controllable inverter circuit connected downstream of the intermediate circuit converts the smoothed voltage from the intermediate circuit into, for example, a three-phase alternating voltage (u, v, w). Each phase has rectangular pulses with a short period / pulse length (e.g., approx. 20 µs - approx. 500 µs), a steep edge (e.g., approx. 100 V / µs - approx. 1000 V / µs), and a pulse amplitude of several hundred volts (e.g., approx. 120 V - approx. 560 V) to supply the electric machine. For this purpose, controlled half-bridge (or full-bridge) circuits with GTO thyristors or IGBT transistors are provided in the inverter circuit. Their time- and phase-correct control defines the speed, torque, or supply current of the electric machine.

[0025] It should be understood that systems with operating voltages in the range of extra-low voltage (up to 50 V AC, up to 120 V DC), low voltage (400 V, 500 V, 690 V), medium voltage and high voltage (3000 V, 3300 V, 5000 V, 5500 V, 6000 V, 6300 V, 6600 V, 10000 V, 10500 V, 11000 V) must also be equipped with the present solution.

[0026] The solution presented here is based on the fact that the condition of the line, and thus also the measure of its failure probability, can be extracted from the rectangular voltage pulses fed into the electrical supply line by the frequency converter using the acquisition and evaluation device. This eliminates the need for an external or separate signal generator. The reflection profile of the line is evaluated using the acquisition and evaluation device (assuming the appropriate edge steepness of the rectangular pulses from the frequency converter). In one variant, the acquisition and evaluation device is a signal processor with an analog-to-digital converter assigned to the input side. In another variant, the acquisition and evaluation device is formed by components that are part of the frequency converter.Voltage reflections resulting from disturbances along the supply line to the connected electrical machine must therefore be recorded in the line's reflection profile, as these disturbances manifest themselves as voltage jumps in one phase (measured against ground) or between two phases. These voltage jumps occur, in the case of essentially rectangular pulses, at the transition from the pulse rise to the pulse plateau. These voltage jumps are – for a given line – all the more pronounced the greater the temporal gradient of the voltage pulse (ΔU / Δt) from the frequency converter; they are processed in the recording and evaluation device.

[0027] At the end of the steep pulse rise, the reflection profile shows a decrease in the gradient during the transition to the pulse plateau. The pulse plateau initially has a first flat section. At the end of the first flat section, a further significant pulse rise follows the second flat section of the pulse plateau. The duration of the first flat section, between the end of the steep pulse rise and the pulse rise at the end of the first flat section, is representative of the length of an intact, e.g., new, cable between the frequency converter and the electrical machine. In one variant of the device, this duration is recorded and evaluated by the recording and evaluation unit.

[0028] From the end of the steep pulse rise at the transition to the first flat section, the line capacitance influences the voltage curve of the pulse. In the first flat section, the characteristic impedance of the line remains essentially constant. The pulse rise at the end of the first flat section represents the reflection of the pulse at the electrical machine, more precisely, the impedance jump at the stator coils of the electrical machine; in one variant of the device, it is recorded and evaluated by the recording and evaluation device.

[0029] This time interval between the transition to the first flat section and the voltage pulse increase at the end of the first flat section, as well as the voltage curve within this section, is a measure of the location and extent of a failure, wear and / or aging of the line in an operating line. Such degradation of the line along the route leads to an earlier or later pulse increase at the end of the first flat section. This is due to, for example, the (real or complex) resistance of the line changing, for example increasing, in the area of ​​line weakening. Such line weakening can be caused by intensive flexing, bending, twisting or kinking of the line at one point or in one area, for example in a drag chain or in the joint of a robot arm.The frequency converter pulse is reflected by this increased resistance / impedance of the line at this point or in this area, leading to a pulse increase at the faulty point in the line within the first flat section. This shortening / lengthening of the first flat section up to the voltage pulse increase is indicative of the location of the line degradation; in one variant of the device, it is detected and evaluated by the detection and evaluation device.

[0030] In the event of a cable break, the voltage pulse rises steeply to its maximum amplitude. A cable break (interruption of power transmission to the electrical machine) is assumed if the cable is electrically shorter, i.e., the location of the damage is not the end of the cable based on the reflection profile. In one variant of the device, this electrically shorter length is detected and evaluated by the detection and evaluation device.

[0031] A gentle, increasing and increasingly steep increase in the voltage amplitude within the first flat section over the operating period compared to the initially recorded voltage signal curve is indicative of the location of the degradation under mechanical stress on the cable; in one variant of the device, it is recorded and evaluated by the recording and evaluation device.

[0032] In one variant, the detection and evaluation device in the device is designed and configured to evaluate a decrease and / or steeper drop from the first flat section over the operating period compared to the initially detected course of the voltage signals as a representative measure for the location or area of ​​the degradation of the feed line.

[0033] In one variant, the device associated with the acquisition and evaluation unit is assigned a data acquisition unit that provides a measure of a speed, a torque, or a number of revolutions after the electrical machine has started up. In one variant, the acquisition and evaluation unit is additionally or alternatively configured and designed to begin acquisition and evaluation of the voltage signal curve at a predefined speed of the electrical machine. This makes the measurement more accurate, since it always takes place at a defined reference value for the speed, torque, etc.

[0034] In one variant, the detection and evaluation device in the device is configured and designed to detect and evaluate the voltage signal profile between two phases during a time period of maximum voltage difference between the two phases. This also improves the quality and accuracy of the measurement.

[0035] In one variant, the detection and evaluation device in the device is set up and designed to be connected to a stepper motor as an electrical machine.

[0036] As a stepper motor, the electrical machine can be designed as a reluctance, permanent magnet, or hybrid stepper motor, which is designed as a 2-, 3- or 5-phase, uni- or bipolar machine to be controlled in normal, wavedrive, half-step, or microstep operation, and / or which is designed to move to very precise angular positions due to a high number of poles.

[0037] The frequency converter may comprise a stepper motor controller which is designed to operate a stepper motor by switching steep-edged rectangular pulses.

[0038] In one variant, the present solution relates to an arrangement comprising an electric motor, a supply line of the electric motor, arranged between the electric motor, and a frequency converter which is configured and intended to supply the electric machine with a single-phase or multi-phase alternating voltage with preferably variable voltage amplitude and rotating field frequency via the electrical supply line, wherein a change in pulse duration / modulation depth and / or voltage amplitude of the alternating voltage serves to change a rotational speed or torque of the electric machine. The frequency converter is configured and intended to provide each phase of the alternating voltage as a sequence of rectangular pulses with a high edge steepness for supplying the electric machine.A detection and evaluation device is configured and programmed to detect and process a voltage signal profile on at least one or between at least two wires of the electrical supply line in order to obtain from the voltage signal profile a measure of the probability of occurrence of a failure, wear and / or aging of the line, and to output the obtained measure at an output.

[0039] In a further variant, the detection and evaluation device is designed to differentiate between fault types such as "impairment of the insulation layer" and "incipient wire breakage", for example by evaluating inductive and / or capacitive resistance values ​​of the cable.

[0040] One variant for determining a measure of the location and extent of a failure, wear, and / or aging of the line uses a device of the type described above to provide meaningful characteristics for the line. During an operational phase of the method, the characteristics of the line are determined (and stored if necessary) and compared with the associated stored threshold values ​​and their number of stored permissible exceedances / undershoots, and / or a measurement profile with a reference reflection profile. This is done using the following calculation rule: Char = ∫ 0 L sl U Puls akt l − U Puls ref l 2 dl

[0041] This is Char the integral over the squared difference of the current voltage of the pulse U pulse akt(l) during operation and the reference voltage U pulse ref(l) over length 0 ... L slof the feed line. In other words, the original reflection profile is subtracted from the current curve, squared, and integrated over the length of the feed line. In one variant of the device, the area of ​​the difference between the two curves is thus captured, evaluated, and calculated by the acquisition and evaluation device.

[0042] Alternatively or additionally, in a variant of the method, degradation profiles measured in the past on corresponding lines and under corresponding conditions are stored. These stored degradation profiles have meaningful sections or points and preferably range from the commissioning of the line to its failure. By adapting these stored degradation profiles by means of appropriate calculated stretching / compression, inclination, and displacement by respective variables based on the meaningful sections or points to a current degradation profile of a line that has not yet reached the point of line failure, a period or point in time is determined for the failure of the line or another meaningful event in the service life of the line, and if applicable, a probability at which this failure or event will occur.In addition to or instead of the calculated stretching / compression, inclination, and displacement by respective variables, computer-aided pattern recognition can also be used to provide a prediction of failure or another significant event in the service life of the line based on characteristic sections or locations of a current degradation curve that has not yet reached failure, compared to one or more stored degradation curves. These calculations / computer-aided pattern recognition are recorded and evaluated by the recording and evaluation device in one variant of the device.

[0043] In one variant of the device for monitoring an electrical power line, it is determined during operation whether the respective characteristic of the line is below the upper and / or above the lower threshold values. If the threshold is yes, the next characteristic in time is determined, and if the threshold is no, a counter is incremented for comparison with the respective number of stored permissible over- / under-limits, possibly within a specified time interval. If the threshold is reached, an alarm is activated / issued.

[0044] In a variant of the device for monitoring an electrical supply line, the probability of failure, wear and / or aging of the line is signalled as increased during the operating phase, depending on the number of activated alarms.

[0045] In a variant of the device for monitoring an electrical supply line, in the operating phase, depending on how often an alarm is activated, the probability of occurrence of failure, wear and / or aging of the line is converted into remaining switching cycles, remaining operating time / service life by relating the characteristics with reference characteristics from the past, for example from a test run or other lines in operation or in the past.

[0046] Such a device allows (quasi-)continuous monitoring, in particular of moving supply cables of electrical machines in industrial devices and systems. However, stationary cables, for example in aggressive environments, can also be proactively monitored using this device. This enables continuous or interval monitoring of supply cables subject to external influences in industrial machines and systems or in land or aircraft. The device also allows the monitoring of a supply cable of a servo motor, for example of a machine tool, a (multi-axis) machining center, a gantry or arm robot, in order to predict failure, wear, and aging of the cable. The measure of the probability of failure, wear, and / or aging of the cable can be evaluated continuously or with repeated sampling, even during ongoing operation of the machine / system.The measure of the probability of occurrence can be calculated as a function of measured values ​​of the signal waveform. In one variant, the signal waveform is the curve of the supply voltage from the frequency converter to the electrical machine. In one variant, the signal waveform of the supply voltage is recorded at the output of the frequency converter, i.e. at the input of the supply line to the electrical machine. In a first measuring period (immediately) after the line has been installed, an initial signal waveform of the supply voltage flowing through the line to the electrical machine can be recorded. This signal waveform can then be offset against later signal waveforms of the supply voltage during operation in order to determine the measure of the probability of failure, wear and / or aging of the line. This initial signal waveform of the supply voltage flowing through the line to the electrical machine is saved and serves as a reference.

[0047] The definition of the components implemented in the device and the programming for recording and evaluating the function from measured signal waveform values ​​can depend on the type of cable, the location and purpose of the cable, whether the cable is moving or stationary, the ambient atmosphere, etc. In one variant, the signal waveform of the pulse signals supplied by the frequency converter for operating the electrical machine, i.e. the useful signal, is evaluated. This makes continuous or interval monitoring or sampling particularly easy and without impacting the operation of the electrical machine. On the one hand, the cable is available exclusively for ongoing system operation. On the other hand, there is no competition or interference with the useful signals sent over the cable during ongoing operation due to fed-in diagnostic data.However, in one variant it is also possible to convert, output and evaluate electrical energy from the intermediate circuit through the inverter circuit into a dedicated measurement signal package instead of the pulse signals for operating the electrical machine.

[0048] The data obtained with the device / method are used to predict failure, wear and aging phenomena of the line.

[0049] The device and method variants presented here evaluate the acquired data during ongoing system operation. From this data, a measure is determined that can be used to initiate predictive maintenance of the electrical line. The device and method can be used to assess the condition of the line and, if necessary, eliminate weak points before they lead to line failure with all its negative consequences. This line diagnosis is non-destructive to the line.

[0050] External influences on the feed line include electromagnetic fields, mechanical stress, deformations (bending, kinking, stretching, compression, torsion, etc.), temperature changes, humidity, aggressive atmospheres, exposure to oil, halogen or salt water, etc.).

[0051] The variants presented here are more cost-effective than the state of the art and offer comparatively more reliable prediction results, as they are continuously evaluated and, in addition, the measurement is performed on the line actually in use (unlike methods with additional sensor elements). This allows for reliable detection of line degradation.

[0052] In one variant, degradation profiles are stored in the device from past measurements on corresponding lines and under corresponding conditions. These degradation profiles have significant sections or points and range from the commissioning of the line to its failure. By adapting the stored degradation profiles through appropriate computational stretching / compression, inclination, and displacement by respective variables in the electronic control unit and / or the signal processor based on the significant sections or points to a current degradation profile of a line that has not yet reached the point of line failure, a period or point in time is determined for the failure of the line or another significant event in the line's service life, and if applicable, a probability with which this failure or event will occur.

[0053] In one variant of the device, the electronic control unit is part of the signal processor or is connected to it separately as part of the device to receive and process the measured characteristics. In another variant, the device is integrated into the frequency converter or uses its components and functionalities to perform the measurements and evaluate them.

[0054] A method disclosed here is used to monitor a supply line of an electrical machine powered by a frequency converter in order to predict failure, wear, and / or aging of the electrical supply line. This method comprises the steps of: routing the electrical supply line to connect an electrical machine in an industrial machine or system or in a land or aircraft to the frequency converter.

[0055] Setting up the frequency converter to supply the electrical machine with a single-phase or multi-phase alternating voltage with variable voltage amplitude and pulse duration via the electrical supply line, whereby a change in pulse duration and / or voltage amplitude of the alternating voltage serves to change a speed or torque of the electrical machine.

[0056] Provide each phase of the alternating voltage as a sequence of rectangular pulses to feed the electrical machine through the frequency converter.

[0057] Detecting and processing voltage signals present on one or between two wires of the electrical supply line by a detecting and evaluating device in order to obtain from the voltage signals a measure of the probability of occurrence of a failure, wear and / or aging of the line, and outputting the obtained measure at an output.

[0058] The above variants of the solution are partly disclosed in device terminology. It is understood that the solution variants disclosed here are also disclosed and can be implemented as methods.

[0059] A method disclosed here for monitoring an electrical line to predict failure, wear, and / or aging of the line is implemented in one variant using a device of the type described above. After laying / installing the supply line between the frequency converter and the electrical machine, a reference reflection profile is recorded and stored. Short description of the characters

[0060] Further features, properties, advantages, and advantages of the devices and methods can be found in the following description in conjunction with the drawings. Possible modifications will also become clear to a person skilled in the art from the following description, which refers to the accompanying drawings. The figures show embodiments of the devices discussed here.

[0061] Here we show: Fig. 1 a schematic representation of an installation comprising a frequency converter operated on the mains to which a supply line subject to external influences is connected in order to control an electrical machine; Fig. 2 a schematic representation of the voltage applied to a phase of the supply line when driving the electrical machine; and Fig. 3a schematic enlarged representation of the voltage applied to a phase of the supply line when controlling the electrical machine at the beginning and at advanced times of operation of the supply line exposed to external influences. Detailed description of variants of devices and procedures

[0062] Fig. 1illustrates a device 10 for monitoring a multi-core supply line 12 of a frequency converter-fed electrical machine M. This device 10 serves to predict failure, wear, and / or aging of the electrical supply line 12. The electrical supply line 12 is laid to connect the electrical machine M, for example in a machine tool, to a frequency converter 14. The frequency converter 14 supplies the electrical machine M with a three-phase alternating voltage uvw via the electrical supply line 12. The alternating voltage uvw has a variable voltage amplitude and variable pulse duration. A change in the pulse duration and / or voltage amplitude of the alternating voltage etc. serves to determine a speed or torque of the electrical machine MThis change is achieved by specifying actual speed signals from the electric machine to an electronic control unit (ECU) and by outputting target speed signals to the frequency converter 14. This configuration is used particularly in systems with encoders. Configurations without a signal being fed back to the electronic control unit (ECU) are also in use. In this case, the electronic control unit (ECU) derives the speed / torque from the motor parameters.

[0063] The frequency converter 14 provides each phase of the alternating voltage as a sequence of rectangular pulses with a high edge steepness to supply the electrical machine. A detection and evaluation device 20 detects, in the variant shown here, between two wires v , wthe electrical supply line 12 a course of the voltage signals in order to process them. The detection and evaluation device 20 is in a variant not further illustrated with the electronic control ECU and / or the electronics of the frequency converter 14. The detection and evaluation device 20 determines a measure of the probability of failure, wear, and / or aging of the supply line 12 from the voltage signal profile on the wires. The obtained measure is output at an output D.

[0064] The electrical machine M here is an internally running motor which is operated from the frequency converter 14, for example as a synchronous or asynchronous machine.

[0065] Using this device 10 and the method described in detail below, a line diagnosis of the feeder line 12 can be performed. This feeder line 12 is an electrically conductive copper line exposed to external influences, with multiple cores, a collective shield, insulating layers, and sheathing. This feeder line 12 supplies current to the three-phase machine M, here in a delta connection, as a three-core line with a ground connection at the shield.

[0066] The detection and evaluation device 20 uses the voltage signals supplied to it from the wires of the feed line 12 to determine the reflections occurring there. These reflections occur in the case of line faults when the (complex) resistance of the feed line 12 is not longitudinally homogeneous or, as a result of the fault, becomes a function of location. Since, in the event of degradation, the reflection factor is different at any point along the line's length, the detection and evaluation device 20 determines the location of the line fault(s) from the reflections that occur.

[0067] Along the longitudinal extent of the feed line 12, the reflection factor changes non-linearly, caused by degradation during operation of the feed line 12. This results in the reflection profile of the feed line 12. This reflection profile, resulting from the recorded voltage signal profile, is determined by the detection and evaluation device 20.

[0068] The frequency converter 14 supplies the electrical machine (synchronous or asynchronous machine) with power at a variable speed depending on the load. To do so, the frequency converter 14 converts the uniform AC mains voltage (e.g., 400 volts, 50 hertz) using a rectifier, first into a DC voltage of the intermediate circuit, and then, using an inverter, into a pulse-modulated AC voltage with variable amplitude and pulse duration. The effective value of this pulse-modulated AC voltage corresponds to that of a sinusoidal AC voltage. By controlling the pulse duration and voltage, a continuous control of the speed or torque of the electrical machine is possible. M possible.

[0069] The frequency converter 14 has a rectifier bridge circuit 14a on the input side. This rectifier bridge circuit 14a converts the three-phase AC mains voltage L1, L2, L3 into a pulsating DC voltage. This pulsating DC voltage is smoothed in a DC voltage circuit 14b, referred to as the intermediate circuit, by a buffer capacitor C and, if necessary, an inductor.

[0070] A controllable inverter circuit 14c connected downstream of the intermediate circuit 14b converts the smoothed voltage from the intermediate circuit 14b into a three-phase voltage u, v, w. In the variant shown here, each phase has rectangular pulses with a short pulse length of, for example, approx. 20 µs - approx. 500 µs. The rectangular pulses have a high edge steepness of, for example, approx. 100 V / µs - approx. 1000 V / µs and several hundred volts pulse amplitude, here, for example, approx. 120 V - approx. 400 volts to supply the electrical machine M. For this purpose, controlled half- (or full-)bridge circuits with GTO thyristors or IGBT transistors, not shown in detail here, are provided in the inverter circuit 14c. These are controlled in the correct time and phase to determine an actual speed rpm is the electrical machine M to achieve, also based on a speed target signal rpm should or another parameter, for example torque, from the electronic control ECU. Thesteering ECU defines, if necessary, from external, not further illustrated specifications, the speed, torque or supply current of the electrical machine M .

[0071] The condition of the supply line 12 exposed to external stress and thus also the measure of its failure probability is to be determined from the rectangular voltage pulses fed into the electrical supply line 12 by the frequency converter 14 by the recording and evaluation device 20. The rectangular voltage pulses SP are the operating energy fed into the supply line 12 for the electrical machine. M The reflection profile of the feed line 12 is to be recorded and evaluated by means of the recording and evaluation device 20. In the reflection profile of the feed line 12, voltage reflections due to disturbances along the feed line 12 to the connected electrical machine are thus Mto detect, since the defects appear as voltage jumps in a phase u, v, w or between two phases u , w can be detected.

[0072] Fig. 2 illustrates the rectangular voltage pulses SP that occur in each of the three phases u, v, w the electrical machine M This pulse pattern is measured at the output of the frequency converter 14. The Fig. 2 The recognizable waveform is imposed on the essentially rectangular voltage pulses SP by a superimposed wave train resulting from the charge reversal processes of capacitor C in the intermediate circuit 14b. In this variant, this superimposed wave train has a period of approximately 6 milliseconds. The additional pulsation occurring at each individual voltage pulse SP has a period of approximately 200 µs in this variant.

[0073] In Fig. 2 and 3It is illustrated how the above-mentioned voltage jumps occur and how they are caused. The frequency converter 14 supplies the three phases u, v, w- with supply line 12 not connected and without electric machine M - as rectangular voltage pulses. These voltage jumps occur when - the supply line 12 is connected and with an electrical machine M - at the transition Ü a first increase in pulse PA1 of the rectangular voltage pulse into the pulse plateau PP These voltage jumps are – for a given line of a given length and capacitive and inductive line coating – all the more pronounced the greater the temporal gradient of the voltage pulse (ΔU / Δt) from the frequency converter 14; they are detected and evaluated by the detection and evaluation device 20.

[0074] The reflection profile shows at the end of the transition Ü with the first increase in pulse PA1a decrease in the gradient during the transition to the pulse plateau. The pulse plateau PP initially has a first flat section FA1. At the end of the first flat section FA1 A further significant increase in pulse follows PA2 to the second flat section FA2 the pulse plateau PP. The duration k * Ls / of the first flat section FA1 between the end of the steep pulse increase PA1 to the pulse increase at the end of the first flat section FA1 is representative of the length of an intact, e.g. new, feeder line 12 Ls / between the frequency converter 14 and the electric machine M. This does not include a factor with the dimension m / s. In one variant of the device, this time period is recorded and evaluated by the recording and evaluation device 20.

[0075] From the end of the first pulse increase PA1 at the transition to the first flat section FA1The line capacitance influences the voltage curve of the pulse. In the first flat section FA1 the characteristic impedance of the line is essentially constant. The pulse increase PA2 at the end of the first flat section FA1 represents the reflection of the pulse at the electrical machine M , more precisely the impedance jump at the stator coils of the electrical machine M ; the impedance jump is detected and evaluated in a variant of the device 10 by the detection and evaluation device 20. This time interval between the transition into the first flat section FA1 and the voltage pulse increase at the end of the first flat section FA1is a measure of the line length for an operational feeder line 12. With progressive degradation of the feeder line 12, voltage peaks occur within this flat section, deviating from the original horizontal course of a new line, which may indicate reflections at growing faults. Such degradation of the feeder line 12 along the route may lead to an earlier pulse rise at the end of the first flat section. FA1 This can be the case, for example, if the fault is located near the end of the line. However, the fault can also occur in the middle of the line, in which case specific curves arise, with an earlier pulse increase in the middle of the first flat section. FA1.

[0076] The (real or complex) resistance of the feeder line 12 increases in the area of ​​line attenuation. The pulse from the frequency converter 14 is reflected at this increased resistance / impedance of the feeder line 12 at this point or in this area, resulting in the pulse increase at the end of the first flat section. FA1. This changes the first flat section FA1 until the pulse rises at the end of the first flat section FA1 compared to the initially recorded voltage signal curve. From this change, the detection and evaluation device 20 calculates the location of the degradation of the feed line 12. In the event of a break in the feed line 12, the voltage pulse rises steeply to the maximum amplitude (second flat section FA2 the pulse plateau PP)This results in an "electrically shorter length" of the supply line 12. The detection and evaluation device 20 evaluates the signals in terms of a line break (at least an almost complete interruption of the energy transmission to the electrical machine M ) if the feed line 12 has an electrically shorter length than its original length Ls / has . This is illustrated by the curves Deg0, Deg1, Deg2 in the Fig. 3 The change in the shape of the curves is recorded and evaluated by the recording and evaluation device 20. In the illustrated example, the damage to the feed line 12 is evident from the curves Deg1 and Deg2 visible; it occurs in the last third of the cable length. Here, for example, a section of the feeder cable 12 may be located in a drag chain, where it is subjected to mechanical stress. In the two-dotted line curve Deg2the curve rises sharply until the second flat section FA2 to the maximum amplitude. Here, a break in the feed line 12 is assumed; the line has a shorter electrical length.

[0077] During an initial operating phase, approximately immediately after installation during initial commissioning, the acquisition and evaluation device 20 acquires and stores characteristics of the feed line 12. These characteristics include, for example, changes in the voltage signal profiles. These changes are compared with the associated stored threshold values ​​and their number of stored permissible overshoots / undershoots, and / or a measurement profile with a reference reflection profile. This is done using the following calculation rule: Char = ∫ 0 L sl U Puls akt l − U Puls ref l 2 dl

[0078] This is Char the integral over the squared difference of the current voltage of the pulse U pulseakt(l) during operation and the reference voltage U pulse ref(l) over length 0 ... L l of the cable. Depending on the application and the cable length, thresholds or limit values ​​are set to signal degradation or a request to replace the cable in a timely manner.

[0079] In another type of evaluation, the initial measurement also serves as a reference profile, which is recorded and saved for each cable core. The voltage level of the first flat section FA1 is set as 100% value and corresponds to an intact feeder line 12. The voltage level of the second flat section FA2 is set as a 0% value and corresponds to a defective feeder line 12. During the degradation of the feeder line 12, in areas where the voltage level of the first flat section FA1should prevail, voltage pulses with an amplitude between the voltage level of the second flat section FA2 and the stress level of the first flat section FA1 If these amplitudes exceed a predetermined level, for example, 70%, the detection and evaluation device 20 also evaluates this as unacceptable aging and signals this accordingly, should it occur a predetermined number of times within a measurement period.

[0080] The variants of the device described above, their construction and operating aspects, as well as the variants of the procedure, serve only to improve understanding of the structure, mode of operation, and properties; they do not restrict the disclosure to the exemplary embodiments. The figures are partly schematic and proportions are not restrictive. Important properties and effects are sometimes shown significantly enlarged in order to clarify the functions, operating principles, technical designs, and features. Each mode of operation, each principle, each technical design, and each feature disclosed in the figures or in the text can be incorporated into all claims, each feature in the text, and in the other figures., other modes of operation, principles, technical embodiments and features contained in this disclosure or resulting therefrom can be freely and arbitrarily combined so that all conceivable combinations can be assigned to the described procedure. This also includes combinations between all individual embodiments in the text, i.e. in every section of the description, in the claims and also combinations between different variants in the text, in the claims and in the figures. The claims also do not limit the disclosure and thus the possible combinations of all the features shown with one another. All disclosed features are explicitly disclosed here, both individually and in combination with all other features.

Claims

1. A device (10) for monitoring a supply line (12) of an electrical machine (M) fed by a frequency converter (14) in order to predict failure, wear and / or ageing of the electrical supply line (12) from a sequence of square pulses fed by the frequency converter (14) for operating the electrical machine (M), wherein - the electrical supply line (12) is arranged and routed to connect an electrical machine (M) in an industrial machine or plant or in a land or air vehicle to the frequency converter (14), and - the frequency converter (14) is arranged and intended to feed the electrical machine (M) with a single-phase or multi-phase AC voltage (u, v, w) with variable voltage amplitude and pulse duration through the electrical supply line (12), wherein a change in pulse duration and / or voltage amplitude of the alternating voltage (u, v, w) is used to change a speed or torque of the electric machine (M), - the frequency converter (14) is set up and intended to provide each phase of the AC voltage (u, v, w) as a sequence of square-wave pulses with a high edge steepness for feeding the electrical machine (M), and wherein a detection and evaluation device (20) is set up and programmed to -- detect and process voltage signals at the output of the frequency converter on one or between two wires of the electrical supply line (12) in order to obtain from the voltage signals a measure of a probability of occurrence of a failure, wear and / or ageing of the line, and -- output the measure obtained at an output (D).

2. The device (10) according to claim 1, wherein the electrical machine (M) is configured as an internally or externally running synchronous or asynchronous machine, and / or wherein the supply line (12) is a metallically conductive copper line or cable with one or more cores or core pairs of the same or different cross-section, individual or collective shielding, insulating layers and / or sheathing, and / or wherein the supply line (12) for a single-phase electrical machine (M) is configured as a two-wire arrangement, and for a three-phase electrical machine (M) is configured with three wires and a ground line; and / or wherein the detection and evaluation device (20) is set up and programmed to evaluate voltage pulses from the frequency converter from the detected voltage signals and pulses superimposed on the voltage pulses by reflections in the electrical supply line (12) at one or between two wires of the electrical supply line (12) in order to determine a reflection profile resulting from the detected course of the voltage signals; and / or wherein the frequency converter (14) is arranged to supply the electrical machine (M) with electrical energy by converting substantially uniform mains AC voltage into an AC voltage with variable amplitude and pulse duration and supplying it to the electrical machine (M) via the supply line (12), wherein the speed or torque of the electrical machine (M) can be varied by controlling the pulse duration and voltage of supplied voltage pulses; and / or wherein the frequency converter (14) has on the input side a rectifier circuit (14a) which is set up to convert incoming mains AC voltage with one or more phases (L1, L2, L3) into a pulsating DC voltage, and / or wherein the rectifier circuit (14a) is followed by an intermediate circuit (14b) which smoothes the pulsating DC voltage; and / or wherein the intermediate circuit (14b) is followed by an intermediate circuit (14b), which smoothes the pulsating DC voltage; and / or wherein a controllable inverter circuit (14c) is arranged downstream of the intermediate circuit (14b), which is set up to convert the smoothed voltage from the intermediate circuit (14b) into a single-phase or multi-phase three-phase voltage (u, v, w), each phase having square-wave pulses with a pulse length of about 20 µs - 500 µs, a high edge steepness of about 100 V / µs - about 1000 V / ps, and a pulse amplitude in the range of low, medium or high voltage for feeding the electrical machine (M); and / or wherein the detection and evaluation device (20) determines the state of the line from the voltage pulses fed into the electrical supply line (12) by the frequency converter (14), wherein the detection and evaluation device (20) determines and evaluates a reflection profile of the line (12); and / or wherein the detection and evaluation device (20) detects and evaluates the interference points as voltage jumps in a phase to ground or between two phases, wherein it evaluates in particular such voltage jumps which occur in substantially rectangular pulses at the transition (aa) of the steep pulse rise (PA1) into a pulse plateau, and / or which occur in substantially rectangular pulses at the transition of a pulse plateau (aa) into a steep pulse fall; and / or wherein the detection and evaluation device (20) detects and evaluates a decrease in the gradient at the end of the steep pulse rise (PA) upon transition into the first pulse plateau (PP1); and / or wherein the detection and evaluation device (20) - detects and evaluates an initial first flat section (FA1) of the pulse plateau (PP), and / or - detects and evaluates a further pulse rise (PA2) to a second flat section (FA2) of the pulse plateau (PP) at the end of the first flat section (FA1), and in doing so - evaluates the length of the time duration of the first flat section (FA1) between the end of the steep pulse rise (PA1) to the further pulse rise (PA2) at the end of the first flat section (FA1) with an intact supply line (12) as a representative measure of its length between the frequency converter (14) and the electrical machine (M); and / or wherein the detection and evaluation device (20) - evaluates the further pulse rise (PA2) at the end of the first flat section (FA1) as a reflection of the pulse at the electrical machine (M), and evaluates the time interval between the transition into the first flat section (FA1) and the further pulse rise (PA2) at the end of the first flat section (FA1) in the case of a line in operation as a measure of the location and extent of a failure, a shortening of the first flat section (FA1) up to the further pulse rise (PA2) at the end of the first flat section (FA1) compared to the initially detected course of the voltage signals as a representative measure of the location or the range of degradation of the supply line (12); and / or wherein the detection and evaluation device (20) - evaluates a detection of an electrically shorter length of the feed line (12) than the previously determined electrical length of the supply line (12) in its intact state as a line break; and / or wherein the detection and evaluation device (20) - evaluates a gentle, increasing and / or increasingly steeper rise from the first flat section over the operating time compared to the initially detected course of the voltage signals as a representative measure of the location or range of degradation of the supply line (12).

3. The device (10) according to any one of claims 1 to 2, wherein the detection and evaluation device (20) - evaluates a decreasing and / or steeper drop from the first flat section over the operating time compared to the initially detected course of the voltage signals as a representative measure of the location or range of degradation of the supply line (12).

4. The device (10) according to any one of claims 1 to 3, wherein the detection and evaluation device (20) is assigned - a data detection means which provides a measure of a rotational speed or a number of revolutions after the electrical machine (12) has started up, and / or - the detection and evaluation device (20) is set up and configured to start detecting and evaluating the profile of the voltage signals at a predefined rotational speed of the electrical machine (12).

5. The device (10) according to any one of claims 1 to 4, wherein the detection and evaluation device (20) - is set up and configured to carry out a detection and evaluation of the course of the voltage signals between two phases (u, v, w) in a time period of maximum difference of the voltage between both phases.

6. The device (10) according to any one of claims 1 to 5, wherein the electric machine is configured as a stepper motor in a reluctance, permanent magnet or hybrid stepper motor design, which is configured as a 2-, 3- or 5-phase, unipolar or bipolar machine to be controlled in normal, wavedrive or half-step or microstep operation, and / or which is configured to approach very precise angular positions due to a high number of poles.

7. The apparatus (10) according to any one of claims 1 to 6, wherein the frequency converter comprises a stepper motor controller adapted to operate a stepper motor by switching steep-edged square pulses.

8. The device (10) according to any one of claims 1 to 7, wherein the detection and evaluation device (20) - in a first operating phase of the supply line (12) determines and stores its characteristics, and - in a second operating phase of the supply line (12) compares its stored characteristics with respectively associated stored threshold values as well as its number of stored permissible overshoots / undershoots, and / or compares a measurement profile with a reference reflection profile.

9. The device (10) according to any one of claims 1 to 8, wherein the detection and evaluation device (20) - in a first operating phase of the supply line (12), determining and storing reference voltages as a reference reflection profile as a characteristic, and - in a second operating phase of the supply line (12), comparing its stored reference voltages of the reference reflection profile with respectively associated stored threshold values as well as its number of stored permissible overshoots / undershoots with a current operating measurement profile, and thereby preferably determining the integral over the squared difference of the current voltage of the pulse during operation and the reference voltage over the length of the line.

10. The device (10) according to any one of claims 1 to 9, wherein the detection and evaluation device (20) - degradation curves which have been measured on corresponding lines and under corresponding conditions in the past and which have significant sections or locations are stored, and wherein the detection and evaluation device (20) is set up and programmed to adapt these stored degradation curves by means of corresponding computational stretching / compression, inclination, displacement by respective variables on the basis of the stored significant sections or points to a current degradation course of a line which has not yet reached the failure of the line, in order to determine for a failure or another significant event in the service life of the line a period of time or a point in time and, if appropriate, a probability at which this event will occur.

11. The device (10) according to any one of claims 1 to 10, wherein in the detection and evaluation device (20) - degradation curves measured on corresponding lines and under corresponding conditions in the past are stored, which have meaningful sections or locations, and wherein the detection and evaluation device (20) is set up and programmed for this purpose, to provide a prediction of a failure or of another significant event in the service life of the line from characteristic sections or locations of a current degradation course of a line, which has not yet reached the point of failure of the line, in comparison with one or more stored degradation courses, by means of pattern recognition procedures from stored degradation courses.

12. The device (10) according to any one of claims 1 to 11, wherein the detection and evaluation device (20) - for monitoring the electrical supply line (12) in the operating phase, determines whether the respective characteristic of the electrical supply line (12) is below upper and / or below lower threshold values, determines the next respective characteristic in time in the case of a yes, in the case of a no, increases a counter for comparison with the respective number of stored permissible overshoots / undershoots, if applicable within a predefined time interval, and activates / outputs an alarm in the case of an overshoot.

13. The device (10) according to any one of claims 1 to 12, wherein the detection and evaluation device (20) - for monitoring the electrical supply line (12) in the operating phase, depending on how often an alarm is activated, the probability of occurrence of failure, wear and / or ageing of the electrical supply line (12) is converted into remaining switching cycles, remaining operating time / lifetime by relating the characteristics to reference characteristics from the past, for example from a test run or other lines that are or have been in operation.

14. The apparatus of any one of claims 1 to 13, wherein the electronic control unit (ECU) is part of, or separately connected to, the signal processor (DSP) as part of the apparatus to receive and process the detected characteristics.

15. A method of monitoring a supply line (12) of an electrical machine (M) fed by a frequency converter (14) to predict failure, wear and / or ageing of the electrical feed line (12) from a sequence of square pulses fed by the frequency converter (14) to operate the electrical machine (M), comprising the steps of: - routing the electrical supply line (12) to connect an electrical machine (M) in an industrial machine or plant or in a land or air vehicle to the frequency converter (14), and - setting up the frequency converter (14) to supply the electrical machine (M) through the electrical supply line (12) with a single-phase or multi-phase alternating voltage (u, v, w) with variable voltage amplitude and pulse duration, wherein a variant of pulse duration and / or voltage amplitude of the AC voltage (u, v, w) serves to vary a speed or torque of the electric machine (M), - providing each phase of the alternating voltage (u, v, w) as a sequence of square-wave pulses with for feeding the electric machine (M) by the frequency converter (14), and wherein - detecting and processing voltage signals applied to one or between two wires of the electric supply line (12) by a detection and evaluation device (20), to obtain from the voltage signals a measure of an occurrence probability of a failure, wear and / or ageing of the line, and - outputting the obtained measure at an output (D).