Method for detecting voltage-dependent faults in an electrical winding system

Description

[0001] The present invention relates to a method for detecting voltage-dependent faults in an electrical winding system according to the preamble of claim 1 and a device.

[0002] Such methods are known from the prior art; a relevant prior art document is JP 2007 108058 A. They are used to detect interturn short circuits and insulation faults within an electrical winding in electrical winding systems, such as electric motors or generators. For this purpose, for example, a charged capacitor is discharged relatively quickly in parallel with the electrical winding to be tested. This generates a relatively high voltage in the electrical winding for a relatively short time, the so-called surge voltage pulse. The energy stored in the capacitor discharges into the inductance. The energy then stored in the inductance discharges back into the capacitor. Due to damping losses, this process can be measured as a damped oscillation at the terminals of the electrical winding.The measured voltage waveform can be used to draw conclusions about the quality of the electrical winding and the insulation system. In an intact winding, the voltage waveform has a typical frequency and a characteristic amplitude. The voltage waveform of an intact electrical winding system is used as a reference and compared with a winding system under test. In the event of deviations outside specified limits, the electrical winding can be detected as defective.

[0003] When comparing the reference winding and the winding under test, a 100% identical result cannot be expected, as small differences between the windings arise due to manufacturing tolerances. Therefore, it may not always be possible to accurately attribute a deviation between the reference winding and the winding under test to the correct cause, and to clearly distinguish whether the cause is a manufacturing tolerance or a minor voltage-dependent error.

[0004] In order to detect very small voltage-dependent faults, it is well known to use the winding under test as a reference. The test is started with a surge voltage pulse with a small peak voltage at which the voltage-dependent fault does not yet occur. The peak voltage is then increased step by step on the winding under test. The measured voltage curve is compared with the previously measured voltage curve. With this method, the percentage change for the same voltage step size becomes smaller at higher peak voltage values, which in turn can lead to small voltage-dependent faults going undetected. This can be compensated for by reducing the voltage increase per step. However, this can result in a relatively long test duration.

[0005] This is where the invention comes in.

[0006] It is the object of the present invention to propose a method in which voltage-dependent faults, in particular small voltage-dependent faults, are detected in an electrical winding system.

[0007] The object is achieved by a method according to claim 1 and by a device according to claim 15.

[0008] The method for detecting voltage-dependent faults in an electrical winding system comprises at least the following steps: Delivery of at least two impulse voltage pulses to the electrical winding system, each impulse voltage pulse having a different peak value U tmeasuring voltage curves on the winding system after each emission of a surge voltage pulse, wherein the voltage curves each comprise a damped oscillation, wherein each voltage curve is caused by one of the surge voltage pulses, storing the voltage curves, wherein a first voltage curve caused by a first of the surge voltage pulses is used as a reference to calculate a calculated second voltage curve caused by a second of the surge voltage pulses, the calculated second voltage curve and the measured second voltage curve are compared with one another, and if there is a difference between the calculated and the measured second voltage curve above a limit value, a voltage-dependent fault in the electrical winding system is detected.

[0009] The first measured voltage waveform, caused by the first surge voltage pulse, is used to calculate a second calculated voltage waveform. The second measured voltage waveform, caused by the second surge voltage pulse with a different peak value than the first surge voltage pulse, is compared with the calculated voltage waveform. If the difference between the two voltage waveforms is above a certain threshold, a voltage-dependent fault can be detected.

[0010] Advantageously, the voltage curves are measured via at least two electrical contacts of the winding system.

[0011] The special feature of this method is that the measured second voltage waveform is compared with a calculated second voltage waveform. Based on the first measured voltage waveform, the measurement result following the second impulse voltage pulse is calculated in advance and used for comparison.

[0012] It can be provided that the peak value of the second surge voltage pulse is formed by the peak value of the first surge voltage pulse plus a voltage increase. The first surge voltage pulse begins with a peak value that is sufficiently small that the voltage-dependent error does not occur. The peak value of the second surge voltage pulse is therefore advantageously greater than the peak value of the first surge voltage pulse.

[0013] Furthermore, it can be provided that the calculated second voltage curve is calculated from the first voltage curve multiplied by a scaling factor. In this case, a linear behavior of the electrical winding system is assumed for the range between the first surge voltage pulse and the second surge voltage pulse. Each voltage value of the first voltage curve is multiplied by a scaling factor. The scaling factor can, for example, be calculated from the peak values ​​of the two surge voltage pulses.

[0014] For reliable detection of a voltage-dependent fault in an electrical winding system, it is often not sufficient to apply two impulse voltage pulses to the electrical winding system. Therefore, it can be provided that n impulse voltage pulses are applied to the electrical winding system, with each of the n impulse voltage pulses having a different peak value. U tmHere, it can be provided that the peak value of the mth surge voltage pulse is formed by the peak value of the m-1st surge voltage pulse plus a voltage increase. The voltage increase can have a constant value or can increase or decrease from voltage pulse to voltage pulse. Here, it is also possible for the voltage increase to follow a nonlinear function.

[0015] It is possible that the calculated m. stress curve is calculated according to the formula Spannungsverlauf m berechnet = Spannungsverlauf m − 1 gem essen ∗ f where Voltage curve calculated is the calculated voltage curve of the m. impulse voltage pulse, where Voltage curve m -1 measured is the measured voltage curve of the m-1st impulse voltage pulse, where f is the scaling factor and where 2 ≤ m ≤ n.

[0016] For all voltage waveforms caused by the second to the nth impulse voltage pulse, a calculated mth voltage waveform is calculated.

[0017] It can be provided that the scaling factor is calculated as f = U t m U t m − 1 , where U tm is the peak value of the m. impulse voltage pulse and U t m-1 is the peak value of the m-1st surge voltage pulse. The scaling factor is therefore always calculated as a function of the voltage increase between two surge voltage pulses. In the event that the voltage increase between individual surge voltage pulses is not constant, calculating the scaling factor as a function of the voltage increase ensures that the different voltage increases are reflected in the scaling factor. This increases the accuracy of the voltage curve calculation.

[0018] This calculated m. stress curve is compared with the measured m. stress curve and the difference is determined. In this case, it can be provided that, to compare the calculated and measured m. stress curves, a reference area is calculated as an integral of the calculated m. stress curve, an area is calculated as an integral of the measured m. stress curve and a difference area is calculated as the difference between the reference area and the area, whereby the difference area represents the difference between the calculated and measured m. stress curve. Since the stress values ​​of each stress curve can take on both positive and negative values ​​and therefore both positive and negative partial areas result, the determination of the reference area and the area can be carried out in a simplified case by adding the individual partial areas as an amount without a sign.

[0019] For a better comparison of the individual differential areas, it is advantageous to compare a percentage value. Therefore, it may be possible to calculate an error area ratio from the differential area and the reference area according to the formula EAR m = A diff ∗ 100 % A ref takes place, whereby A ref the reference surface is, A m the area is and A diff is the differential area. The special feature of the error area ratio is that the differential area is calculated based on the calculated m. stress curve compared to the measured m. stress curve.

[0020] It can also be provided that an expected error area ratio is calculated, whereby the expected error area ratio is deducted from the calculated error area ratio EAR mis subtracted and the difference between the expected defect area ratio and the calculated defect area ratio is compared with the limit value. In an optimally manufactured winding system, the difference would be 0%. To determine the expected defect area ratio, the defect area ratio of the first two measured voltage curves is first calculated and then extrapolated to the subsequent voltage curve, which is caused by an impulse voltage pulse with a higher peak voltage value. It should be noted that the calculated reference area and the area become smaller with an increase in the peak voltage value, since the percentage deviation between the peak values ​​of the individual impulse voltage pulses decreases.

[0021] It can be provided that a fault area ratio is calculated for each of the m calculated and measured voltage curves. If all differences between the expected fault area ratios and the calculated fault area ratios of the m voltage curves are compared, the differences fluctuate within a narrow range around 0%, preferably between -5% and +5%, for an intact winding system without a voltage-dependent fault. If the magnitude of the fault area ratio is above a limit, preferably above 15%, a voltage-dependent fault is detected. In such a case, no further surge voltage pulses are applied to the winding system.

[0022] Furthermore, it can be provided that each fault area ratio calculated from the m calculated and measured voltage curves is standardized. For this purpose, it can be provided that the fault area ratios are standardized using a standardization factor. If all standardized fault area ratios of the m voltage curves are compared with one another, the standardized fault area ratios for an intact winding system without voltage-dependent faults fluctuate within a narrow range of 1%, advantageously between -2% and +4%. If the amount of the standardized fault area ratio lies above a limit value, in particular above 5%, a voltage-dependent fault is detected. In such a case, no further impulse voltage pulses are applied to the winding system.

[0023] It can be provided that the normalization factor is calculated according to the formula U t m − 1 U t m − U t m − 1 ∗ 100 is calculated, where U tmis the peak value of the m. impulse voltage pulse and U t m-1 is the peak value of the m-1st surge voltage pulse. The normalization factor is therefore always calculated as a function of the peak values ​​of the surge voltage pulses and thus indirectly as a function of the voltage increase between two surge voltage pulses. In the event that the voltage increase between individual surge voltage pulses is not constant, calculating the normalization factor as a function of the voltage increase ensures that the different voltage increases are reflected in the normalization factor.

[0024] It is also possible to calculate a reference area as an integral of the measured first voltage curve, to calculate an area as an integral of the measured second voltage curve, to calculate a difference area as the difference between the reference area and the area, where the difference area represents the difference between the measured first and the measured second voltage curve, to calculate an error area ratio from the difference area and the reference area according to the formula EAR 2 = A diff 2 ∗ 100 % A ref 2 takes place, whereby A ref 2 is the reference surface of the measured first voltage curve and A diff2 is the differential area, which represents the difference between the measured first and the measured second voltage curve, the error area ratio is compared with an upper and a lower limit value and if the upper limit value is exceeded or the lower limit value is undershot, a voltage-dependent error in the electrical winding system is detected.

[0025] For all m voltage curves, it can be provided that the difference between the measured mth voltage curve and the measured m-1st voltage curve is calculated, where 2 ≤ m ≤ n,n-1 upper limit values ​​are defined and n-1 lower limit values ​​are defined, with an upper and a lower limit value being assigned to each of the differences, whereby the limit values ​​are calculated from the mean value of the differences plus and minus a permissible deviation. The permissible deviation varies depending on the application. The permissible deviation can be between 5% and 15%. If one of the differences falls below the corresponding lower limit value or if one of the differences exceeds the corresponding upper limit value, a voltage-dependent fault in the electrical winding system is detected. It is conceivable that the difference between the measured mth voltage curve and the measured m-1st voltage curve is determined by calculating m error area ratios. An upper and a lower limit value can then be defined for each error area ratio.For example, if the defect area ratios and the upper and lower limits are plotted in a diagram, a kind of envelope of upper limits and an envelope of lower limits are created, enclosing the defect area ratios. If a defect area ratio exceeds this envelope, a stress-dependent defect is detected.

[0026] A device for detecting voltage-dependent faults in an electrical winding system, comprising at least one means for generating a surge voltage pulse, connections for an electrical connection of the device to the electrical winding system, a storage means, wherein the storage means is designed to receive, store and provide measurement data of the voltage curves, an evaluation means, wherein the evaluation means is designed to compare the measurement data of the voltage curves provided by the storage means and to calculate auxiliary variables with the provided measurement data of the voltage curves, wherein the device is designed to carry out a method according to the invention.

[0027] Further features and advantages of embodiments of the invention are described below with reference to the drawings. The same reference numerals are used for identical or similar parts and for parts with identical or similar functions. It shows: Fig. 1 a flowchart of a method according to the invention

[0028] It is not necessary for a method according to the invention to have all of the features described below. It is also possible for a method according to the invention to have only individual features of the exemplary embodiment described below.

[0029] Fig. 1 shows a flowchart illustrating the detection of voltage-dependent faults in an electrical winding system according to the present invention.

[0030] First, fault detection is initiated. For this purpose, a peak value of a surge voltage pulse is set. The peak value of the surge voltage pulse depends on the electrical winding system being tested and must be selected to ensure that no voltage-dependent fault occurs in the electrical winding system.

[0031] The surge voltage pulse, more precisely defined by the peak value, is applied to the electrical winding system. One approach to this can be to connect a charged capacitor relatively quickly in parallel with the winding under test. This generates a relatively high voltage in the winding for a relatively short time, the so-called surge voltage pulse. The surge voltage pulse has an adjustable peak value. The energy stored in the capacitor discharges into the inductance. The energy then stored in the inductance discharges back into the capacitor. In response to the surge voltage pulse, a damped oscillation is generated, which is measured as a voltage waveform across electrical contacts in the electrical winding system.

[0032] The measured voltage waveform is stored. For this purpose, a storage device can be provided that is designed to receive, store, and provide measurement data of the voltage waveforms. The measured voltage waveform is used to calculate a calculated voltage waveform of another surge voltage pulse. To calculate the calculated voltage waveform, according to the exemplary embodiment of the invention, the measured voltage values ​​of the measured voltage waveform are multiplied by a scaling factor.

[0033] A check is then made to determine whether at least two measured voltage waveforms have been stored in the memory. If the query is answered with "no," the flowchart begins again with the setting of a peak value for the surge voltage pulse. This peak value differs from the previous peak value by a voltage increase. The voltage increase varies depending on the electrical winding system being tested and must be set individually.

[0034] After the second surge voltage pulse is delivered, the voltage waveform caused by the surge voltage waveform is measured and stored in the storage means.

[0035] The measured second waveform is also used as a reference to calculate a calculated voltage waveform of the next surge voltage pulse.

[0036] The measured second voltage curve is compared with the calculated second voltage curve, and the difference between the two voltage curves is determined. This can be done in an evaluation device that is designed to compare the measured data of the voltage curves provided by the storage device and to calculate auxiliary variables using the provided measured data of the voltage curves. The calculated auxiliary variables can, for example, be the error area ratio between the two voltage curves to be compared. The calculated error area ratio can, in turn, be compared with an expected error area ratio. It is also possible to calculate a standardized error area ratio as an auxiliary variable. A wide variety of methods are conceivable for comparing the calculated and measured voltage curves. The aim here is to determine the difference between the two voltage curves.

[0037] If the amount of the difference is above a specified limit, whereby the limit may vary depending on the type of electrical winding system to be tested, a voltage-dependent fault is detected and fault detection is terminated.

[0038] If the difference is below this specified limit, the process starts again by setting a peak value for another surge voltage pulse. In this case, it would be the third surge voltage pulse. The third voltage waveform measured upon delivery of the third surge voltage pulse would then be saved and used to calculate a calculated fourth voltage waveform. The measured third voltage waveform itself is compared with the calculated third voltage waveform calculated in the previous process. Here, too, a check is carried out to determine whether the difference between the calculated third voltage waveform and the measured third voltage waveform lies above a specified limit. If this is the case, a voltage-dependent fault is detected and fault detection is aborted. If this is not the case, the process starts again.

[0039] It goes without saying that fault detection is terminated after a finite number of surge voltage pulses. If the magnitude of the difference in none of the cycles exceeded the specified limit, the electrical winding system is recognized as intact.

Claims

1. Method for detecting voltage-dependent faults in an electrical winding system, comprising at least the following steps: - outputting at least two surge voltage pulses to the electrical winding system, wherein each surge voltage pulse has a different peak value Ut, - measuring voltage curves at the electrical winding system after outputting a respective surge voltage pulse, wherein the voltage curves each comprise a damped oscillation, each voltage curve being caused by one of the surge voltage pulses, - storing the voltage curves, characterized in that - a first voltage curve, which is caused by a first of the surge voltage pulses, is used as a reference, for calculating a calculated second voltage curve, which is caused by a second of the surge voltage pulses, - the calculated second voltage curve and the measured second voltage curve are compared with one another, - in the case of a difference between the calculated and the measured second voltage curve above a limit value a voltage-dependent fault is detected in the electrical winding system.

2. Method according to claim 1, characterized in that the peak value of the second surge voltage pulse is formed by the peak value of the first surge voltage pulse plus a voltage increase.

3. Method according to claim 1 or 2, characterized in that the calculated second voltage curve is calculated from the first voltage curve multiplied by a scaling factor.

4. Method according to any one of claims 1 to 3, characterized in that n surge voltage pulses are output to the electrical winding system, wherein each of the m surge voltage pulses has a different peak value Utm.

5. Method according to claim 4, characterized in that the calculated mth voltage curve is calculated according to the formula voltage curve m calculated = voltage curve m − 1 measured ∗ f wherein voltage curvemcalculated is the calculated voltage curve of the mth surge voltage pulse, wherein voltage curvem-1measured is the measured voltage curve of the m-1th surge voltage pulse, wherein f is the scaling factor and wherein 2≤m≤n.

6. Method according to any one of claims 4 to 5, characterized in that the scaling factor is calculated as f = U t m U t m − 1 , wherein Utm is the peak value of the mth surge voltage pulse and Utm-1 is the peak value of the m-1th surge voltage pulse.

7. Method according to any one of claims 4 to 6, characterized in that for comparison of the calculated and measured mth voltage curve, - a reference area is calculated as the integral of the calculated mth voltage curve, an area is calculated as the integral of the measured mth voltage curve, - a difference area is calculated as the difference between the reference area and area, wherein the difference area represents the difference between the calculated and the measured mth voltage curve.

8. Method according to claim 7, characterized in that a calculation of a fault area ratio from the difference area and the reference area is madea ccording to the formula, EARm = Adiff ∗ 100 % Aref wherein Aref- is the reference area, Am is the area and Adiff is the difference area.

9. Method according to claim 8, characterized in that an expected fault area ratio is calculated, wherein the expected fault area ratio is subtracted from the calculated fault area ratio EARm and a comparison is made between the difference between the expected fault area ratio and calculated fault area ratio with the limit value.

10. Method according to claim 8, characterized in that a fault area ratio is calculated for each of the m calculated and measured voltage curves.

11. Method according to claim 10, characterized in that the fault area ratios are normalized by means of a normalization factor.

12. Method according to claim 11, characterized in that the normalization factor is calculated according to the formula U t m − 1 U t m − U t m − 1 ∗ 100 , wherein Utm is the peak value of the mth pulse voltage pulse and Utm-1 is the peak value of the m-1th pulse voltage pulse.

13. Method according to claim 1, characterized in that - a reference area is calculated as the integral of the measured first voltage curve, - an area is calculated as an integral of the measured second voltage curve, - a difference area is calculated as the difference between the reference area and area, wherein the difference area represents the difference between the measured first and the measured second voltage curve, - a calculation of a fault area ratio is made from the difference area and the reference area according to the formula EAR 2 = A diff 2 ∗ 100 % A ref 2 wherein Aref2 is the reference area of the measured first voltage curve and Adiff2 is the difference area representing the difference between the measured first and the measured second voltage curve, - the fault area ratio is compared with an upper and a lower limit value and a voltage-dependent fault in the electrical winding system is recognized if the upper limit value is exceeded or if the value falls below the lower limit value.

14. Method according to claim 4, characterized in that - the difference between the measured mth voltage curve and the measured m-1th voltage curve is calculated, wherein 2≤m≤n, - n-1 upper limit values are determined and n-1 lower limit values are determined, wherein an upper and a lower limit value are each assigned to one of the differences, wherein the upper limit values are calculated from the mean value of the differences plus an allowed deviation and the lower limit values minus an allowed deviation, - a voltage-dependent fault in the electrical winding system is recognized if one of the differences falls below the associated lower limit value or if one of the difference exceeds the associated upper limit value.

15. Device for detecting voltage-dependent faults in an electrical winding system, comprising at least one means for generating a surge voltage pulse, terminals for an electrical connection of the device to the electrical winding system, a memory means, wherein the memory means is configured to receive, store and provide measurement data of the voltage curves, an evaluation means, wherein the evaluation means is configured to compare the measurement data of the voltage curves provided by the memory means and to calculate auxiliary variables with the measurement data provided by the voltage curved, wherein the device is configured to perform a method according to any one of the preceding claims.