Monitoring a sychronous motor

Abstract

In a method for monitoring a synchronous motor, in particular for monitoring an excitation device of the synchronous motor, an individual value dependent on the power factor of the synchronous motor is measured, wherein a monitoring value (3) is formed from a multiplicity of individual values and / or values dependent thereon. The method can be carried out by means of a monitoring device.

Description

[0001] Description

[0002] MONITORING A SYNCHRONOUS MOTOR

[0003] The invention relates to a method and a device for monitoring a synchronous machine, in particular a method and a device for monitoring an excitation device of a synchronous machine. In particular, the invention relates to a method for detecting a faulty excitation device in a synchronous motor in mains or converter operation, wherein mains operation is also referred to as DOL operation (direct switching on the mains).

[0004] Synchronous machines are electrical machines that can be used as synchronous motors or synchronous generators. Synchronous machines can be self-excited or separately excited. Separately excited synchronous machines have an excitation device. Self-excited synchronous machines in particular have permanent magnets for excitation. When operating a synchronous machine, attention must be paid to the power factor. In alternating current technology, the power factor (also called the active power factor) is the ratio of the active power P to the apparent power S. For sinusoidal alternating quantities, the active factor is defined as the ratio of active power P to the apparent power S. This is also known as coscp. In synchronous motors in mains or converter operation, the power factors can be adjusted or set using the excitation device.In general, a power factor of 1 can be assumed, as this is the optimal value from the point of view of losses and torque provision. In principle, the motor can also be operated at other operating points; this must be taken into account in the algorithm (variable or static setpoint specification of the power factor). It is often not possible to optimally set the excitation circuit during the commissioning phase, as not all points can be reached during test operation. A suboptimal setting is not immediately problematic for the operator if the performance in terms of torque is sufficient. The excitation control loop can, under certain circumstances, be seen as secondary. A faulty or incorrectly parameterized excitation device or a defective excitation device leads in particular to anomalies in the power factor.

[0005] One object of the invention is to detect an error, an anomaly, or a defect. The error(s) particularly concern a faulty and / or incorrectly parameterized excitation device and / or a defective excitation device. The object particularly concerns a synchronous motor.

[0006] A solution to the problem arises from a method according to claim 1, a monitoring device according to claim 11 or a computer program product according to claim 12.

[0007] In a method for monitoring a synchronous machine, in particular a synchronous motor, in particular for monitoring an excitation device of a synchronous machine, in particular a synchronous motor, an individual value which is dependent on the power factor of the synchronous machine or of the synchronous motor is measured, a monitoring value being formed from a large number of individual values ​​and / or values ​​dependent thereon. The individual value is therefore, for example, the power factor itself. The individual value can also be formed from a large number of individual values. By monitoring individual values ​​and forming a monitoring value from the individual values, an anomaly can be detected automatically. This is also possible during long-term operation of the synchronous machine.When monitoring over a long period of time, the power factor is not monitored from one grid period to the next, but over longer periods of minutes, hours, days, weeks or months. This enables automated identification of anomalies during long-term operation of, for example, a synchronous motor with an excitation device. A "normal" or "abnormal" status, which describes the current health of the excitation device, can thus be made available. The potential for saving losses alone for larger motors is in the region of 50,000 kWh per year. This results in considerable savings potential over the life cycle. Monitoring is therefore particularly important for synchronous machines with higher outputs of several hundred kilowatts or several megawatts.

[0008] Long-term recording of the excitation values ​​of synchronous motors can result in, or even enables, an automated evaluation of the power factor. Anomalies can be identified automatically within a short period of time. A change (e.g., repair) to the excitation system is also automatically detected based on the data. The error status, for example, is reset accordingly.

[0009] The monitoring value is in particular a difference between a target value for the power factor and the determined power factor, or even a difference thereof. The determined power factor is an example of an individual value. The monitoring value can be determined, for example, as follows. Power values ​​LI to LI O are determined at intervals over a period of time. Furthermore, a target power value L-target of 1 is specified, for example, although other target values ​​for the power value can also be set (e.g. 0.9). L-target minus LI results in a first intermediate monitoring value ZW1 (L-target - LI = ZW1). L-target minus L2 results in a second intermediate monitoring value ZW2. Adding the intermediate monitoring values ​​ZW1 to ZW10 results in a total error sum W. The total error sum W can be regarded as a monitoring value.

[0010] Automated monitoring eliminates the need to have the power factor manually monitored by experts. For example, an analysis of a time series at irregular intervals can be used to classify the current state of health. For monitoring purposes, static limits for the power factor can also be set in one embodiment, although this can lead to false indications at certain operating points. For example, a static analysis sets a fixed limit, and if the power factor falls below this limit, a warning is issued. Errors can also arise from a manual evaluation of the limit values ​​over time. This requires very specific expert knowledge, which presupposes in-depth data aggregation. An analysis can involve a high level of personnel expenditure.With manual monitoring, very long periods of operation must be manually observed and evaluated with regard to exclusion criteria. This problem can be overcome by creating a monitoring value, which is composed of or depends on a large number of individual values, with the individual values ​​depending on performance factors within a period.

[0011] In one embodiment of the method, individual values ​​are used to form the monitoring value, for example by calculation, i.e. in particular a large number of individual values ​​are used which are determined or have been determined in a static operating state of the synchronous motor. A static operating state of the synchronous motor is, for example, an operating state in which the speed, in particular the target speed, of the synchronous motor changes only slightly. A slight change in the speed occurs, for example, when the revolutions change by less than 10 revolutions / min within 1 minute. Another example of a slight change in the speed is when the speed changes by less than 1 percent within 1 minute.

[0012] In one embodiment of the method, individual values ​​which are or have been determined in a dynamic operating state of the synchronous motor are excluded from the calculation of the monitoring value. A dynamic operating state is, for example, the start-up of the electric motor or the shutdown of the synchronous motor. A dynamic operating state of the synchronous motor exists, for example, when the speed of the synchronous motor changes by more than 10 revolutions / min within 1 minute. Another example of a dynamic operating state is a speed change of more than 1 percent within 1 minute. The use of the synchronous motor is particularly characterized by the fact that different target speeds and / or different loads are intended during operation.

[0013] When monitoring a synchronous motor, it is particularly important not to monitor the cosfactor absolute value using limit values, since the cosfactor can assume different values ​​at different operating points, such as in dynamic operating conditions. It may be important for the monitoring in question to consider how the power factor develops or changes over time in static conditions.

[0014] In one embodiment of the method, the synchronous motor operates at different target speeds. The method can therefore be used to monitor how the power factor develops over time at different target speeds in static operating states. A synchronous motor, in particular, must be maintained in an energetically optimal operating state. To do this, the power factor must be monitored. For a synchronous motor, optimal energy utilization occurs at a cos cp equal to 1.

[0015] In one embodiment of the method, the plurality of individual values ​​are taken from a period of time which is in particular freely definable, the period of time in particular having a length of at least one minute or a length of minutes to months. The time interval between the individual values ​​used within the period of time can be, for example, one or more seconds (in particular greater than one second) or one or more minutes (in particular greater than one minute). The interval is in particular adjustable. The interval is, for example, 10 seconds to 120 seconds. In this case, in particular only individual values ​​which were determined during stationary operation of the synchronous machine or synchronous motor are considered.

[0016] In one embodiment of the method, the resulting monitoring value is weighted according to time. The monitoring value can thus be calculated from a sum of values, with the values ​​weighted differently depending on age. For example, if a first value Wn and a second value Wn+1 are given, a new value can be calculated using a forgetting factor alpha: Monitoring value = Wn+1 + (Wn * (1-Alpha)), where alpha is less than 1.

[0017] In one embodiment of the method, individual values ​​are used depending on the operating state of the synchronous machine or synchronous motor. Power factors are therefore not taken into account, for example, if they were determined during a run-up of the synchronous machine or synchronous motor. Power factors are taken into account, in particular, if they were determined in a steady-state state of the synchronous machine or synchronous motor.

[0018] However, this evaluation requires expert knowledge, as the power factor deviates from the target value under many operating conditions. This is caused, for example, by motor start-up and shutdown, load changes, and process-related speed setpoint changes. These operating conditions must be taken into account in the evaluation.

[0019] In one embodiment of the method, an anomaly is detected based on the monitoring value, with the anomaly particularly affecting the excitation device. For example, a defective excitation device can be detected.

[0020] In one embodiment of the method, the speed of the synchronous machine or synchronous motor is also taken into account when recording the individual values. For example, the power factor can be multiplied by the sign of the motor speed. This allows monitoring to be independent of the speed.

[0021] In one embodiment of the method, the power factor of the synchronous motor is improved after the anomaly has been detected. This can be achieved, for example, by optimizing the control of the excitation device or by replacing or repairing a component, such as a defective power semiconductor valve or a control module, etc. In one embodiment, a coscp of 1 is achieved again through the optimization.

[0022] In a monitoring device for a synchronous machine or a synchronous motor, in particular for monitoring an excitation device of the synchronous machine or the synchronous motor, the monitoring device is or is integrated into a structural unit of a power converter or into a structural unit of a regulation and / or control system for the synchronous machine or the synchronous motor, wherein the monitoring device can be used to carry out one of the described methods. The structural unit of the power converter is, for example, a control cabinet or a housing. The structural unit of the regulation and / or control system is, for example, a housing or a circuit board.

[0023] A computer program product has programming for carrying out one of the described methods, wherein the computer program product is particularly capable of executing on the monitoring device.

[0024] In the following, the invention is illustrated and explained in more detail using an example figure.

[0025] According to the invention, continuous and context-related monitoring of the power factor is possible. The flowchart illustrates possible individual steps and highlights potential advantages over previous manual problem-solving methods (manual expert monitoring or limit value analysis). According to the invention, all of the steps described below, or just one step, or only a selected portion of the steps described below can be performed:

[0026] Step

[0027] Preprocessing 1 :

[0028] Multiply the new power factor by the sign of the motor speed -

[0029] In the first step, the current power factor is multiplied by the sign of the engine speed. This ensures that negative power factors are not mistakenly identified as faulty. Compared to the previous solution, additional measured values ​​are considered here, which reduces the "false positive" rate ("false positive" rate: points in time that are incorrectly classified as abnormal and thus require unnecessary attention).

[0030] Step

[0031] Filter 2 :

[0032] Consider only timestamps in which the machine, such as the synchronous motor, is operated stationary -

[0033] In the second step, only relevant timestamps of individual values ​​are filtered. In particular, measured values ​​(individual values) that are a certain period of time away from the next off state are considered irrelevant.

[0034] Periods during which the machine is not running (including, for example, start-up and shutdown times) are not included in the analysis, thus reducing the false positive rate. Unlike the previous problem-solving approach, additional information is taken into account and the performance factor is viewed in its overall context, rather than simply classifying its raw values. Step

[0035] Error sum 3:

[0036] Add the power factor deviation to the total error sum, which is first multiplied by a forgetting factor (alpha). After data preparation, the error (the difference between the actual power factor and the expected value of 1) is added to the total error sum. This is then multiplied by a forgetting factor (a < 1), which reduces the weight given to previous errors. This decreases the total error sum over time, and past errors are not carried over into the long run.

[0037] Step

[0038] Limit 4 :

[0039] Detect an anomaly based on a total error sum - If the error sum exceeds a certain value, the time is classified as abnormal. Individual measurement errors are not classified as anomalous. Instead, the errors are summed, and an anomaly is only detected when a certain threshold is exceeded. This approach ensures a reduction in the false positive rate. An anomaly is only detected when an accumulation of unexpected performance factors occurs. Furthermore, larger deviations carry more weight, as the error sum increases more quickly with larger deviations.

[0040] Step

[0041] Maximum error sum 5:

[0042] Make sure that the error sum does not exceed a maximum -

[0043] The error sum is limited to a maximum. This ensures that it does not become too large, thus promptly detecting the need to replace the defective excitation device. The forgetting factor reduces the error sum during normal operation, meaning that after a sufficiently normal measured value is obtained, the status is automatically set to normal. One advantage of the invention may be that, for example, after repairing an excitation device, no manual entry of the repair is required. After a certain period of time, the algorithm automatically detects the change based on the data.

[0044] The described implementations result in automated power factor monitoring. A context-related error sum (e.g., by using only values ​​from steady-state operation) ignores outliers, detects clusters, and dynamically determines changes.

Claims

Patent claims 1. Method for monitoring a synchronous motor, in particular for monitoring an excitation device of the synchronous machine, wherein a single value dependent on the power factor of the synchronous motor is measured, wherein a monitoring value (3) is formed from a plurality of single values ​​and / or values ​​dependent thereon.

2. Method according to claim 1, wherein individual values ​​are used to form the monitoring value (3) which are determined or have been determined in a static operating state of the synchronous motor.

3. Method according to claim 1 or 2, wherein for the formation of the monitoring value (3) individual values ​​are excluded which are determined or have been determined in a dynamic operating state of the synchronous motor.

4. Method according to one of claims 1 to 3, wherein the asynchronous motor has different target speeds during operation.

5. Method according to one of claims 1 to 4, wherein the plurality of individual values ​​are from a period of time which is in particular freely determinable, wherein the period of time in particular has a length of at least one minute or a length of minutes to months.

6. Method according to one of claims 1 to 5, wherein the monitoring value formed is weighted (3) according to time.

7. Method according to any one of claims 1 to 6, wherein individual values ​​are used depending on the operating state (2) of the synchronous motor.

8. Method according to any one of claims 1 to 7, wherein an anomaly is detected by the monitoring value, wherein the anomaly particularly concerns the excitation device.

9. Method according to one of claims 1 to 8, wherein the rotational speed ( 1 ) of the synchronous motor is also taken into account with the individual values.

10. Method according to one of claims 8 or 9, wherein after detection of the anomaly the power factor of the synchronous motor is improved.

11. Monitoring device of a synchronous motor, in particular for monitoring an excitation device of the synchronous motor, wherein the monitoring device is integrated in a component of a power converter or in a component of a control and / or regulation system of the synchronous motor, wherein the monitoring device is usable for carrying out a method according to one of claims 1 to 10.

12. Computer program product for carrying out a method according to one of claims 1 to 10, when executed on a monitoring device according to claim 11.

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