Device for detecting a short-circuit fault in a winding of an electric machine
Patent Information
- Application Number
- EP2023744208
- Authority / Receiving Office
- EP · EP
- Patent Type
- Applications
- Current Assignee / Owner
- Priority Date
- 2022-06-24
- Filing Date
- 2023-06-20
- Publication Date
- 2025-04-30
AI Technical Summary
Existing methods for detecting short-circuits between the turns of electrical machine windings are inefficient, as they often rely on complex signal processing or numerous temperature sensors, making it difficult to quickly and accurately identify faults, especially in machines with permanent magnets.
A device comprising an equipotential wire connecting electrical nodes and a current sensor to measure currents in this wire, which detects short-circuits by comparing the measured current to a threshold at least twice the residual current, allowing for rapid and sensitive detection with minimal equipment.
This solution enables reliable, space-saving, and efficient detection of short-circuits without complex processing, using a single current sensor to monitor all phases, reducing false positives and requiring fewer sensors than traditional methods.
Smart Images
Figure 1.1
Abstract
Description
[0001] Description
[0002] Title of the invention: Device for detecting a short-circuit fault in a winding of an electrical machine
[0003] Technical Field
[0004] The present invention relates to the general field of detecting a short circuit in a winding of an electrical machine, and more particularly the detection of a short circuit between the turns of the windings.
[0005] Prior art
[0006] The windings of electrical machines are made of enameled wires. The enamel and the impregnation varnish provide insulation that can fail in some cases. This can cause a short circuit that appears locally and generates local heating that can cause the copper to melt. It is therefore essential to protect the electrical machine as soon as such a fault is detected. Furthermore, with more and more permanent magnet machines being used, it is becoming increasingly difficult to clear the short circuit using a control. It is therefore essential to detect such a fault quickly to minimize its consequences.
[0007] In the prior art, detection methods are based on the analysis of current or voltage signals. The measured currents are analyzed with signal processing techniques to detect harmonics characteristic of each type of fault. These methods have the advantage of not requiring any special equipment within the electrical machine and of being able to identify the nature of the fault. However, the information is difficult to differentiate from the normal operation of the electrical machine, because the latter already has many imperfections. In addition, each electrical machine has its own "signature" and it is difficult to generalize these methods to several machines.
[0008] Other known methods involve implementing temperature sensors within the windings of the electrical machine to detect heating. However, this requires a large number of sensors due to the very localized nature of heating.
[0009] It is therefore desirable to have a device for rapid and sensitive detection of a short circuit between the turns of a winding of an electrical machine.
[0010] Statement of the invention
[0011] The invention relates to an assembly of an electrical machine comprising at least one phase comprising two electrical paths in parallel, each electrical path of the same phase comprising a winding, the first electrical paths of all the phases being connected to the same first electrical node and the second electrical paths of all the phases being connected to the same second electrical node and means for detecting a short circuit between at least two turns of a winding of a phase, characterized in that the electrical machine comprises an equipotential wire electrically connecting the first and second electrical nodes and a current sensor configured to measure an electric current flowing in the equipotential wire,and in that the detection means are configured to compare the electric current measured by the current sensor to a detection threshold equal to at least twice a residual current flowing in the equipotential wire in the absence of a short circuit between turns of said windings.,
[0012] By measuring the electric current flowing in the equipotential wire, the current sensor measures in particular the electric current circulating between the two electrical paths of the same phase. In addition, thanks to the placement of this equipotential wire connecting the two electrical nodes, the current circulating between the two paths of all phases can be measured. Indeed, as the two electrical paths in parallel within the same phase have an identical voltage, in normal operation, that is to say in the absence of a fault in the electrical machine, the sensor measures a zero or very low electric current (presence of residual noise in practice less than 5% of the nominal current of the machine) because the two parallel paths of the phases are traversed by an identical magnetic flux at all times.If a short circuit occurs between the turns of a winding of any electrical path of a phase, this has the effect of causing a voltage imbalance between the two paths of the phase concerned, since the short circuit between two turns in an electrical path results in a reduced number of turns (one turn less) in this path, and moreover, the short circuit has the effect of reducing the flux in the path which presents the fault (application of Lenz's law). The induced voltage resulting from the product of the number of turns and the flux (Faraday's law) is therefore reduced in the path which presents the fault. In this case, the sensor will measure the appearance of a significant current, in particular a current at least twice higher than the residual current of normal operation, i.e. in the absence of a short circuit between turns.
[0013] The placement of the current sensor at the equipotential wire thus makes it possible to detect a short-circuit fault between the turns of the windings of the electrical machine. In addition, thanks to this equipotential wire, only a single current sensor is required to detect short circuits between the turns in all phases of the electrical machine. Thus, the electrical machine of the invention comprises a means of short-circuit detection that is compact, fast and sensitive compared to a solution as previously explained requiring the integration of a sufficient number of temperature sensors that are effective only if they are placed close to the fault.
[0014] In addition, this current sensor does not require complex processing means to detect a short circuit. It is enough to detect the increase in measured electric current to detect the short circuit. If desired, it will be possible to add filtering means to improve the quality of current measurements.
[0015] According to a particular characteristic of the invention, the current sensor is a current transformer and the equipotential wire is placed in the center of the current transformer.
[0016] This makes it possible to obtain an electrical machine equipped with a compact short-circuit detection means. Since the measured current is almost zero in the absence of an electrical fault, the equipotential wire needs to be sized to withstand a current of the order of the nominal current of the machine for only the measurement and detection time, which may be less than a second. Thus, the equipotential wire is sized for a much lower current rating than the wire of the windings of the electrical machine. For example, it has a cross-section four times smaller than the winding of one of the electrical channels.
[0017] Another object of the invention is a method for detecting a short circuit in an electrical machine according to the invention comprising the measurement of an electric current flowing in the equipotential wire, the determination of a residual electric current flowing in the equipotential wire, and the detection of a short circuit if the measured electric current becomes greater than a detection threshold equal to at least twice the determined residual electric current.
[0018] As explained previously, in the event of a short circuit between the turns of the first electrical path of one of the phases of the electrical machine, the increase in the measured electrical current compared to the residual electrical current makes it possible to detect this short circuit. The detection threshold, at least twice higher than the determined residual electrical current, makes it possible to ensure reliable detection of short circuits, i.e. without detection errors linked to residual noise in the electrical machine in question, the factor two constituting a sufficient margin compared to the residual current (residual noise) to consider that if the current exceeds this threshold there is indeed a proven short-circuit fault in the electrical machine.
[0019] According to a particular characteristic of the invention, the residual electric current is determined in the factory.
[0020] Brief description of the drawings
[0021] Other characteristics and advantages of the present invention will emerge from the description given below, with reference to the appended drawings which illustrate exemplary embodiments thereof which are not in any limiting nature. [Fig. 1] Figure 1 represents, schematically and partially, an electrical machine and means for detecting a short circuit between the turns of the machine according to one embodiment of the invention.
[0022] [Fig. 2] Figure 2 schematically represents a method for detecting a short circuit between two turns in the electrical machine of Figure 1 according to one embodiment of the invention.
[0023] Description of the embodiments
[0024] Figure 1 shows, schematically and partially, the assembly comprising an electrical machine 1000 and means for detecting a short circuit between at least two turns of a winding of a phase of the machine 1000 according to one embodiment of the invention.
[0025] The 1000 electric machine consists of three phases 100, 200 and 300.
[0026] The first phase 100 comprises two electrical paths 101 and 102. Each path 101 and 102 comprises a winding 111, 112. At the input of phase 100, a current 1101+1102 flows, then in the first path 101, the current 1101 flows while in the second path 102, the current 1102 flows.
[0027] The second phase 200 and the third phase 300 also comprise two electrical paths 201, 202 and 301, 302 like the first phase 100. Just like the first phase 100, at the input of the phases 200 and 300, a current flows, then divides between the two paths 201, 202 and 301, 302 of the two phases 200 and 300. Thus, the current 1201 flows in the path 201, the current 1202 flows in the path 202, the current 1301 flows in the path 301 and the current 1302 flows in the path 302.
[0028] Each first electrical path 101, 201, 301 of the three phases 100, 200, 300 is connected to the same first electrical node 10, and each second electrical path 102, 202, 302 of the three phases 100, 200, 300 is connected to the same second electrical node 20.
[0029] The electrical machine 1000 also comprises an equipotential wire 400 electrically connecting the first 10 and second 20 electrical nodes. The machine 1000 comprises a current sensor 500 configured to measure an electric current (1101 + 1201 + 1301) - (1102 + 1202 + 1302) likely to flow in the equipotential wire 400.
[0030] The detection of a short circuit in the electrical machine in operation is based on the measurement of current in the equipotential wire 400 by the current sensor 500. According to the invention, this current measurement by the sensor 500 is compared to a predetermined detection threshold, which is at least equal to twice the residual current value measurable in the absence of an electrical fault.
[0031] The detection of a short-circuit fault allows the electrical machine 1000 to be made safe, for example a short-circuiting of all the phases 100, 200, 300 in order to reduce the short-circuit current between the turns and / or a stopping of the electrical machine by mechanical disconnection of the rotor.
[0032] In normal operation of the machine 1000, the two paths (101, 102), (201, 202) and (301, 302) within the same phase 100, 200 and 300 have the same induced voltage at their terminals because they are traversed by a magnetic flux of the same value at each instant as is customary during paralleling. The current (1101 + 1201 + 1301) - (1102 + 1202 + 1302) flowing in the equipotential wire 400 is therefore zero or almost zero, the presence of a residual current or noise being possible. This residual current is in practice less than 5% of the nominal current of the electrical machine 1000. Thus, in normal operation of the electrical machine 1000, the current (1101 + 1201 + 1301) - (1102 + 1202 + 1302) measured by the single current sensor 500 is zero, or almost zero.
[0033] If a short circuit occurs between the turns of one of the windings 111, 112, 211, 212, 311, 312, the current (1101 + 1201 + 1301) - (1102 + 1202 + 1302) measured by the current sensor 500 will no longer be zero and the increase in current measured by the sensor 500 makes it possible to detect the short circuit.
[0034] For example, in the case where a short circuit appears between the turns of one of the windings 111, 112 of the first phase 110, a non-zero circulating current 1101 - 1102 appears between the channels 101 and 102. It is represented in dotted lines in Figure 1. The current measured (1101 + 1201 + 1301) - (1102 + 1202 + 1302) by the sensor 500 is then equal to 1101-1102. This current measured by the sensor is compared to the detection threshold, allowing the detection of a short-circuit fault and the safety of the electrical machine if necessary.
[0035] This detection according to the invention is achieved by adding a single equipotential wire 400 and a single current sensor 500 measuring the current flowing in this wire 400, and by a comparison based on a detection threshold determined with respect to the residual current measurable in the wire 400 in the absence of an electrical fault, greater than at least twice this residual current, ensuring reliable detection. The equipotential wire 400 and the current sensor 500 thus form a means for detecting a short circuit between at least two turns of a winding of a phase of the electrical machine 1000.
[0036] The electrical machine 1000 having N turns per phase, a short circuit between two turns in an electrical path results in an imbalance in the number of turns in the proportion 1 / N. The current in the equipotential wire 400 in the event of a fault will therefore be higher the lower the number of turns per phase. The invention is thus particularly applicable to machines whose number of turns per phase N is low, for example less than or equal to 50.
[0037] For example, and with reference to Figure 1, if the windings of the electrical paths of a phase each comprise 20 turns, then in the event of a short circuit between two turns of one of these windings, the electrical path concerned will no longer have 19 turns, resulting in an imbalance in the number of turns of 5%. The induced voltages will therefore be different in the two parallel paths solely due to the different number of turns, accentuated by the fact that the magnetic flux in the path with the fault will also be reduced by the effect of the current in the short-circuited turn in accordance with Lenz's law.As a result, the circulating current measured by the current sensor is then significantly higher than the residual current determined, in normal operation, which makes it possible to set a short-circuit fault detection threshold at least twice as high as the residual current determined for the electrical machine, the factor two constituting a sufficient margin compared to the residual current to consider that if the current exceeds this threshold there is indeed a proven fault. Figure 2 schematically represents a method 2000 for detecting a short circuit between two turns in an electrical machine of the invention, for example in the electrical machine 1000 of Figure 1.
[0038] The method 2000 comprises the measurement 2010 of the electric current Imeasure (or of the current (1101 + 1201 + 1301) - (1102 + 1202 + 1302) according to the references of figure 1) circulating in the equipotential wire 400, the determination 2020 of the residual current I reSiduei circulating in the equipotential wire 400 and the detection 2030 of a short circuit when Imeasure is twice as high as I reS iduei- In other words, the detection threshold is at least equal to twice I reS iduei-
[0039] The current Iresiduei corresponds to the residual noise circulating in the equipotential wire 400 during normal operation of the electrical machine 1000, and as explained with reference to figure 1, this residual current I reS iduei is zero or almost zero, in all cases less than 5% of the nominal current in the electrical machine 1000 on average. This residual current is a measurable characteristic of the electrical machine considered. In particular, the determination of this current Iresiduei (step 2020) can advantageously be carried out during characterization tests of the prototype of the electrical machine considered. The value I reSiduei determined for the prototype is the characteristic value Iresiduei of the electrical machines corresponding to this prototype. Alternatively, it is possible to measure I reS iduei on each electrical machine before it is put into service. In other words, the residual current I reS iduei can be determined at the factory.
[0040] Different embodiments of the detection and in particular of the comparison of the current measurement signal supplied by the sensor with a defined detection threshold can be envisaged according to any hardware or software technique known to those skilled in the art. In the case of a software implementation, the residual current measured for the electrical machine (during tests on a prototype or on the machine itself) is a parameter of the machine, for example stored in a register or a memory of the control means of the electrical machine. In the case of a hardware implementation, the comparison circuit is designed to ensure the detection of a current greater than a defined detection threshold, greater than at least twice the residual current determined for the electrical machine in question.Regardless of the embodiment, the electrical machine 1000 may also include a fuse device configured to limit heating of the equipotential wire 400 during a short circuit in the phases 100, 200, 300 of the machine. The electrical machine 1000 has been described with three phases, but it may more generally include N phases, with N an integer greater than or equal to 1.
Claims
Demands
1. An assembly of an electrical machine (1000) comprising at least one phase (100, 200, 300) having two electrical paths (101, 102, 201, 202, 301, 302) in parallel, each electrical path of the same phase having a winding (111, 112, 211, 212, 311, 312), the first electrical paths of all phases being connected to the same first electrical node (10) and the second electrical paths of all phases being connected to the same second electrical node (20) and means for detecting a short circuit between at least two turns of a winding of a phase,characterized in that the electrical machine comprises an equipotential wire (400) electrically connecting the first and second electrical nodes and a current sensor (500) configured to measure an electric current (1101 + 1201 + 1301 - (1102 + 1202 + 1302)) flowing in the equipotential wire and in that the detection means are configured to compare the electric current measured by the current sensor to a detection threshold equal to at least twice a residual current (Iresiduei) flowing in the equipotential wire in the absence of a short circuit between turns of said windings.
2. Assembly according to claim 1, wherein the current sensor is a current transformer and the equipotential wire is placed at the center of the current transformer.
3. A method (2000) for detecting a short circuit in an electrical machine according to any one of claims 1 or 2 comprising measuring (2010) an electric current (Imeasure) flowing in the equipotential wire, determining (2020) a residual electric current (Iresiduei) flowing in the equipotential wire, and detecting (2030) a short circuit if the measured electric current (Imeasure) becomes greater than a detection threshold equal to at least twice the determined residual electric current (Iresiduei). reS iduei)-
4. A detection method according to claim 3, wherein the residual electric current is determined at the factory.