METHOD FOR DETERMINATION OF A LOCATION OF A SHORT CIRCUIT FAULT IN A GENERATOR ARRANGEMENT, GENERATOR ARRANGEMENT, WIND TURBINE, COMPUTER PROGRAM AND ELECTRONICALLY READABLE MEDIUM

Abstract

Provided is a method for determination of a location of a short circuit fault in a generator arrangement, wherein the generator arrangement includes an electrical machine and at least one channel, wherein the or each channel includes a breaker, a converter unit and a set of stator windings of the electrical machine connected to the converter unit via the breaker, wherein upon an occurrence of a short circuit in a channel, the connection between the set of stator windings and the converter unit interrupted by opening the breaker, wherein depending on at least one measured signal of a measurand, wherein the measured signal is measured by at least one sensor of the electric machine and wherein the measurand describes a torque ripple of the electrical machine, either the electrical machine or the converter unit of the channel is determined as location of the short circuit fault.

Claims

1. A method for determination of a location of a short circuit fault in a generator arrangement, wherein the generator arrangement comprises an electrical machine and at least one channel, wherein the or each channel includes a breaker, a converter unit and a set of stator windings of the electrical machine connected to the converter unit via the breaker, wherein upon an occurrence of a short circuit in a channel, the connection between the set of stator windings and the converter unit is interrupted by opening the breaker, characterized in that depending on at least one measured signal of a measurand, wherein the measured signal is measured by at least one sensor of the electric machine and wherein the measurand describes a torque ripple of the electrical machine, either the electrical machine or the converter unit of the channel is determined as location of the short circuit fault.

2. The method according to claim 1, wherein as the at least one sensor of the electric machine, a sensor measuring a vibration and/or an acceleration of at least one component of the electrical machine is used.

3. The method according to claim 2, an accelerometer coupled to a main bearing of the electrical machine and/or to at least one stator plate of the electrical machine is used as sensor and/or that a microphone measuring sound inside the electrical machine is used as sensor and/or that a short circuit torque controller is used as sensor.

4. The method according to claim 1, wherein a comparison value related to an amplitude of the torque ripple is derived from the at least one measured signal of the measurand, wherein the comparison value is compared to a threshold value, wherein the electrical machine is determined as location of the short circuit fault if the comparison value is above the threshold value and the converter unit determined as location of the short circuit fault if the comparison value is below the threshold value.

5. The method according to claim 4, wherein a root-mean-square value of the measured signal or a peak-to-peak value of the measured signal or an absolute value of the measured signal is used as comparison value.

6. The method according to claim 4, wherein the threshold value is determined depending on an average torque of the electrical machine and/or a rotational speed of the electrical machine.

7. The method according to claim 1, wherein the at least one measured signal of the measurand is bandpass filtered, wherein the lower cutoff frequency and/or the upper cutoff frequency of the bandpass filtering are determined in dependence of a rotational speed of the electrical machine.

8. The method according to claim 1, wherein the electrical machine comprises two or more channels, wherein after occurrence of the short circuit fault in a channel, the converter unit of the channel is stopped and the at least one breaker of the channel is opened, or the converter units of all channels are stopped and the breakers of all channels are opened.

9. The method according to claim 1, wherein the electrical machine comprises two or more channels, wherein after occurrence of the short circuit fault in a faulty channel of the channels, if the converter unit determined as location, an operation of the generator arrangement is continued or restarted with the channel or the channels except the faulty channel, wherein if the electrical machine is determined as location the operation is stopped.

10. A generator arrangement comprising an electrical machine, a control unit and at least one channel, wherein the or each channel comprises a means for detecting or detector for an occurrence of a short circuit in the channel, a converter unit and a set of stator windings of the electrical machine connected to the converter unit, wherein the electrical machine includes at least one sensor that measures a measurand describing a torque ripple of the electrical machine, wherein the control unit is configured to perform a method according to claim 1.

11. A wind turbine comprising a generator arrangement according to claim 10.

12. A computer program comprising instructions which, when the program is executed by a control unit of a generator arrangement comprising an electrical machine, a control unit and at least one channel, wherein the or each channel includes a detector for detecting an occurrence of a short circuit in the channel, a converter unit and a set of stator windings of the electrical machine connected to the converter unit, wherein the electrical machine includes at least one sensor that measures a measurand describing a torque ripple of the electrical machine, cause the control unit to carry out a method according to claim 1.

13. An electronically readable medium having stored thereon the computer program of claim 11.

Description

BRIEF DESCRIPTION

[0037] Some of the embodiments will be described in detail, with reference to the following figures, wherein like designations denote like members, wherein:

[0038] FIG. 1 depicts a generator arrangement according to embodiments of the invention;

[0039] FIG. 2 depicts a diagram depicting the torque of an electrical machine in case of a short circuit fault in a converter unit;

[0040] FIG. 3 depicts a diagram depicting the torque of an electrical machine in case of a short circuit fault in the electrical machine;

[0041] FIG. 4 depicts a block diagram of a first embodiment of a method according to embodiments of the invention; and

[0042] FIG. 5 depicts a block diagram of a second embodiment of a method according to embodiments of the invention.

DETAILED DESCRIPTION

[0043] In FIG. 1, a generator arrangement 1 according to embodiments of the invention is shown. The generator arrangement 1 comprises an electrical machine 2, a first channel 3 and a second channel 4. The first channel 3 comprises a converter unit 5 and a breaker 6. Correspondingly, the second channel 4 comprises a converter unit 7 as well as a breaker 8.

[0044] The converter unit 5 of the first channel 3 is connected to a set 9 of stator windings of the electrical machine 2 via the breaker 6. Correspondingly, the second channel 4 comprises a set 10 of stator windings, which is connected to the control unit 7 via the breaker 8. The sets 9, 10 of stator windings are three-phase sets of stator windings. During rotation of the electrical machine 2, hence during a generator operation of the electrical machine 2, a three-phase electrical current is generated in each of the channels 3, 4. The generated three-phase electrical current is converted by the converter units 5, 7 into a DC current. The DC-side of the converter units 5, 7 can be connected to other electrical components and/or electrical circuits and/or a power grid. In this embodiment, on the DC-side of the converters 5, 7 of each channel 3, 4, a capacitor 11, 12 is arranged for frequency filtering. However, further components on the DC-side are omitted in FIG. 1. It is in particular possible that the generator arrangement 1 is used in a power generating device, for instance in a wind turbine.

[0045] The breaker 6 in the first channel 3 can be opened to interrupt the connection between the converter unit 5 and the set 9 of stator windings in case of a short circuit in the first channel 3. Correspondingly, the breaker 8 in the second channel 4 can be opened to interrupt the connection between the converter unit 7 and the set 10 of stator windings in case of a short circuit in the second channel 4. In an embodiment, the breakers 6 and 8 may interrupt simultaneously their respective connections in case of a short circuit in one of the channels 3, 4.

[0046] The generator arrangement 1 comprises further a control unit 13 which is connected to the converter units 5, 7 and the breakers 6, 8. Furthermore, the control unit 13 is connected to a sensor 14 of the electrical machine 2, wherein the sensor 14 measures a measurand describing a torque ripple of the electrical machine 2. The control unit 13 comprises a memory unit for storing of data and/or programs, a communication unit for sending and receiving data and a processor unit for processing the data and/or for executing the programs and/or for controlling the communication unit.

[0047] In this embodiment, the sensor 14 is an accelerometer coupled to a main bearing of the electrical machine 2. By the sensor 14, a vibration caused by the appearance of torque ripple in the electrical machine 2 can be measured, since the vibration measurable by the sensor 14 in the main bearing corresponds to a torque ripple of the electrical machine 2. Additionally or alternatively, also an accelerometer coupled to at least one stator plate of the electrical machine 2 and/or a microphone measuring sound inside the electrical machine 2 and/or a short circuit torque controller can be used as sensor 14.

[0048] If a short circuit appears, for instance, in the first channel 3, the breaker 6 is opened to stop the short circuit current in the first channel 3. The opening of the breaker 6 can be detected and/or commanded for instance by the control unit 13. An operation of the converter unit 5 can be stopped by the control unit 13. The short circuit in channel 3 can occur in the converter unit 5, for instance due to a faulty component in the converter unit 5. It is also possible that the short circuit fault appears in the electrical machine 2, for instance due to an insulation breakdown inside the electrical machine 2 and/or in the set 9 of stator windings. Depending on the location in which the short circuit fault occurs, a different behaviour regarding a torque ripple of the electrical machine 2 occurs. Since the electrical machine 2 is in operation when the short circuit fault occurs, a rotor of the electrical machine 2 is rotating. The rotor comprises a means for generating of a magnetic field, for instance a plurality of permanent magnets, so that after the occurrence of the short circuit fault in the electrical machine 2, a current can be generated in the electrical machine 2 due to the magnetisation of the rotor. In this case, a fault current is flowing in the set 9 of stator windings.

[0049] In the case that the short circuit fault appears in the converter unit 5, no fault current is generated since the connection between the converter unit 5 and/or the stator windings of the set 9 of stator windings is disrupted by opening the breaker 6, and the switching in converter unit 5 is stopped.

[0050] The fault current in the electrical machine 2 causes a torque ripple of the torque of the electrical machine 2. Since the fault current in the electrical machine 2 cannot be measured directly, a measurement of the torque ripple can be used as an indirect measurement of the fault current. The torque ripple can be for instance measured by the sensor 14, which measures a vibration in the main bearing of the electrical machine 2, since, if a torque ripple appears or increases in the torque of the electrical machine 2, also a vibration of the main bearing of the electrical machine 2 can appear or increase, respectively.

[0051] In FIG. 2, a graph depicting the torque of the electrical machine 2 is shown. On the ordinate, the torque M is plotted, depending on the time t which is plotted on the abscissa. At the time t.sub.f, a short circuit fault occurs in channel 3 of the generator arrangement 1. After a few initial peaks, a torque ripple is set up as discernible in the portion 15 of the curve. The curve in FIG. 2 depicts the torque of the electrical machine 2 in case of a short circuit fault in the converter unit 5 of channel 3. The average torque after the occurrence of the short-circuit fault is reduced to approximately half of the value prior to the fault.

[0052] In FIG. 3, the curve of the torque M of the electrical machine 2 for the occurrence of a short circuit fault in the electrical machine 2 is depicted. The short circuit fault appears correspondingly at t.sub.f. However, in case of the occurrence of the short circuit fault in the electrical machine 2, the amplitude of the torque ripple in the portion 16 of the curve exhibits a larger amplitude than in the case of the occurrence of the short circuit fault in the converter unit 5 as depicted in FIG. 2. Due to the different amplitude of the torque ripple of the torque of the electrical machine 2, a differentiation between the electrical machine 2 and the converter unit 5 of the first channel 3 as location of the short circuit fault is possible.

[0053] In FIG. 4 a block diagram of a first embodiment of a method according to the invention is shown. As input variable, a measured signal 17 of a measurand, which describes the torque ripple of the electric machine 2, is used. The measured signal 17 can be measured by the sensor 14 of the electrical machine 2. The measurand can be, for instance, an acceleration measured by the sensor 14 at a stationary ring of a main bearing of the electrical machine 2.

[0054] In block 18, a low pass filtering eliminating a DC bias of the measured signal 17 occurs. After the low pass filtering, the measured signal 17 is high pass filtered in block 19 to remove any HF noise. From the filtered measured signal 17, an absolute value of a ripple in the measured signal 17 corresponding to an absolute value of the torque ripple amplitude is determined in block 20. In block 21, after determination of an absolute value of the ripple in the measured signal 17, a comparison value is determined by averaging the obtained absolute value over a certain interval of time or over an averaging window, respectively. The comparison value is related to an amplitude of the torque ripple or an amplitude of a ripple in the measured signal 17 corresponding to the torque ripple, respectively.

[0055] In block 22, the comparison value is compared to a threshold value, wherein the threshold value can be a fixed value or can be determined depending on an absolute torque or an average torque of the electrical machine 2. The absolute or average torque of the electrical machine 2 can be measured by a torque sensor connected to the control unit 13 or it can be calculated and/or estimated by control unit 13 based on currents and/or voltages in the electrical machine 2 measured and/or controlled by the control unit 13. If the comparison value exceeds the threshold value, the electrical machine 2 is chosen as location of the short circuit fault. Contrary, if the comparison value is below or equal to the threshold value, the converter unit 4 of the first channel 3 is determined as location of the short circuit fault. The functionality of the blocks 18 to 22 can be implemented in the control unit 13 of the generator arrangement 1.

[0056] In FIG. 5, a second embodiment of a method according to the invention is depicted. The method can be conducted by the control unit 13 of the generator arrangement 1. As input variables, again the measured signal 17 measured by the sensor 14 is used. Additionally, a rotor speed signal 23, which is measured by a rotor speed sensor of the electrical machine 2 (not shown) or which is calculated and/or estimated by the control unit 13, is used. In block 24, an adaptive bandpass filtering of the measured signal 17 occurs. Thereby, a lower cutoff frequency and/or an upper cutoff frequency of the bandpass filtering can be adjusted depending on the rotor speed signal 23. By adjusting the lower cutoff frequency and/or the upper cutoff frequency of the bandpass filtering, a certain harmonic of the rotation of the rotor can be filtered from the measured signal. It is for instance possible that a second harmonic of the measured signal 17 is filtered. It is also possible that depending on a type of the electrical machine 2, a fourth harmonic or a sixth harmonic of the measured signal 17 is filtered. Additionally or alternatively, also a centre frequency and/or a damping of the bandpass filtering can be adjusted.

[0057] In block 25, a root-mean-square is calculated from the measured signal 17 as a comparison value. Additionally or alternatively, a root-mean-square value, also the calculation of a peak-to-peak value of the measured signal 17 is possible. The comparison value can be determined depending on the rotor speed signal 23. The determined comparison value corresponds to the torque ripple of the electrical machine 2. The comparison value determined in block 25 is compared to a threshold value in block 22 as described for the first embodiment of the method. It is possible that the threshold value used for the comparison in block 22 is determined depending on an average torque of the electrical machine 2 and/or depending on the rotor speed signal 23. The second embodiment of the method can also be implemented in the control unit 13.

[0058] In both embodiments of the method discussed in the foregoing, it is possible that, after the determination of the location of the short circuit fault, if the converter unit 5 has been determined as location of the short circuit fault, a restarting of the generator arrangement 1 using the second channel 4 is performed, in particular if the breaker 8 was opened upon occurrence of the short circuit fault. It is also possible that in the case that only the breaker 6 of the first channel 3 has opened, an operation of the generator arrangement 1 is continued using the second channel 4. However, if the electrical machine 2 has been determined as location of the short circuit fault, the operation of the generator arrangement 1 is stopped.

[0059] The method is conducted correspondingly if the fault occurs in the second channel 4 instead of the first channel 3. In the case of an electrical machine comprising only one channel, the location of the short circuit fault can be, for instance, stored in a storage the control unit 13, so that prior to a repair of the generator arrangement 1, the localisation of the short circuit can be used to facilitate the repair.

[0060] If the method is applied in a generator arrangement comprising more than two channels, the operation can be continued using all channels except the faulty channel if the converter unit of the faulty channel was determined as location of the short circuit fault. Correspondingly, if the electrical machine 2 has been determined as location of the short circuit fault, the operation of all channels of the generator arrangement 1 is prevented or stopped.

[0061] Although the present invention has been disclosed in the form of preferred embodiments and variations thereon, it will be understood that numerous additional modifications and variations could be made thereto without departing from the scope of the invention.

[0062] For the sake of clarity, it is to be understood that the use of “a” or “an” throughout this application does not exclude a plurality, and “comprising” does not exclude other steps or elements.