Device for detecting short-circuit fault in winding of electric machine

Abstract

The invention relates to an electric machine (1000) comprising at least one phase (100, 200, 300) comprising two electrical paths (101, 102, 201, 202, 301, 302) connected in parallel, each electrical path of a single phase comprising a winding (111, 112, 211, 212, 311, 312), a first electrical path of all phases being connected to a single first electrical node (10) and a second electrical path of all phases being connected to a single second electrical node (20), characterized in that the winding (111, 112, 211, 212, 311, 312) is connected to the first electrical node (10). The electric machine comprises: an equipotential line (400) electrically connecting a first electrical node and a second electrical node; and a current sensor (500) configured to measure a current flowing in the equipotential line (I101 + I201 + I301-(I102 + I202 + I302)).

Description

Technical Field

[0001] The present invention relates to the general field of detection of short circuits in electric machine windings and, more particularly, to detection of short circuits between turns of a winding. Background Art

[0002] The windings of the motors consist of enameled wires. The varnish and the impregnating resin form an insulating layer which, in some cases, can fail. This can lead to local short circuits and generate local heating, which can lead to melting of the copper. Therefore, the motor must be protected immediately as soon as such a fault is detected. In addition, machines with permanent magnets are increasingly used, and it is increasingly difficult to eliminate such short circuits by command. Therefore, such faults must be detected quickly to minimize their consequences.

[0003] In the prior art, detection methods are based on the analysis of current or voltage signals. The measured current is analyzed using signal processing techniques to detect the harmonic signature of each type of fault. The advantage of these methods is that they do not require any specific equipment inside the motor and are able to identify the nature of the fault. However, this information is difficult to distinguish from the normal operation of the motor, as the machine already has many defects. In addition, each motor has its own "signature", and it is difficult to extend these general methods to several machines.

[0004] Other known methods include installing temperature sensors within the windings of the motor to detect heating. However, due to the very localised nature of the heating, this requires a large number of sensors.

[0005] It would therefore be desirable to have a device for quickly and sensitively detecting a short circuit between several turns of a winding of an electric machine. Summary of the invention

[0006] The present invention relates to a component, which has: an electric motor, which includes at least one phase, the at least one phase includes two electrical paths in parallel, each electrical path of the same phase includes a winding, the first electrical paths of all phases are connected to the same first electrical node, and the second electrical paths of all phases are connected to the same second electrical node; and a device for detecting a short circuit between at least two turns of the winding of the phase, characterized in that the electric motor includes: an equipotential line electrically connecting the first electrical node and the second electrical node, and a current sensor configured to measure a current circulating in the equipotential line, and characterized in that the detection device is configured to compare the current measured by the current sensor with a detection threshold, which is equal to at least twice the residual current circulating in the equipotential line in the absence of any short circuit between the turns of the winding.

[0007] The current sensor measures in particular the electrical circulating current between two electrical paths of the same phase, by measuring the current circulating in the equipotential line. Furthermore, due to the placement of this equipotential line connecting two electrical nodes, the circulating current between the two paths of all phases can be measured. Specifically, since the two parallel electrical paths within the same phase have the same voltage, under normal operation (i.e., in the absence of any fault in the motor), the sensor measures zero current or a very small current (in fact, there is a residual noise of less than 5% of the nominal current of the machine), since at any time there is the same magnetic flux passing through the two parallel paths of the phase. If a short circuit occurs between the turns of the winding of any electrical path of the phase, this has the effect of causing a voltage imbalance between the two paths of the phase in question, because the short circuit between two turns in an electrical path manifests itself as a reduction in the number of turns in this path (one less turn), and in addition, because the short circuit has the effect of reducing the magnetic flux in the path where the fault exists (application of Lenz's law). Therefore, in the path where the fault exists, the induced voltage generated by the product of the number of turns and the magnetic flux (Faraday's law) decreases. In this case, the sensor will measure the presence of a significant current, in particular in normal operation (ie in the absence of any short circuit between the turns), said current being at least twice the residual current.

[0008] Placing the current sensor at the equipotential line thus enables detection of short-circuit faults between the turns of the winding of the electric machine. Moreover, thanks to this equipotential line, only a single current sensor is required to detect short-circuits between the turns in all the phases of the electric machine. The electric machine of the invention thus comprises means for detecting short-circuits which are small, fast and highly sensitive compared to the previously described solutions which require the incorporation of a sufficient number of temperature sensors and which are only effective when they are placed near the fault.

[0009] Furthermore, this current sensor does not require any complex processing means for detecting a short circuit. Simply detecting an increase in the measured current is sufficient to detect a short circuit. If necessary, filtering means can be added to improve the quality of the current measurement.

[0010] According to a particular feature of the invention, the current sensor is a current transformer and the equipotential conductor is placed at the centre of the current transformer.

[0011] This makes it possible to obtain an electric machine equipped with a compact device for detecting a short circuit.

[0012] Since in the absence of any electrical fault the measured current is almost zero, the equipotential wire needs to be dimensioned to carry a current in the order of the nominal current of the machine only during the measurement and detection time (which may be less than 1 second). The equipotential wire is therefore dimensioned for a much smaller rated current than the wires of the windings of the motor. For example, its cross-section is four times smaller than that of the winding of one of the electrical paths.

[0013] Another subject of the invention is a method according to the invention for detecting a short circuit in an electric machine, comprising: measuring the current circulating in the equipotential line, determining the residual current circulating in the equipotential line, and detecting a short circuit if the measured current becomes greater than a detection threshold, the detection threshold being equal to at least twice the determined residual current.

[0014] As previously mentioned, in the event of a short circuit between the turns of a first electrical path of one of the phases of the electric machine, the increase in the current measured relative to the residual current makes it possible to detect such a short circuit. The detection threshold is at least twice the residual current determined, making it possible to ensure reliable detection of the short circuit, i.e. without any detection error related to the residual noise in the electric machine in question, the factor of two constituting a sufficient margin relative to the residual current (residual noise) to assume that: if the current exceeds this threshold, there is indeed a confirmed short circuit fault in the electric machine.

[0015] According to a particular feature of the invention, said residual current is determined at the factory. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Other characteristics and advantages of the present invention will become apparent from the description given below, with reference to the accompanying drawings, which illustrate exemplary embodiments without any limitation.

[0017] [ Figure 1 ] Figure 1 The device for detecting an inter-turn short circuit of a machine and a motor according to an embodiment of the present invention are schematically and partially shown.

[0018] [ Figure 2 ] Figure 2 Schematically showing a method for detecting Figure 1 A method of short-circuiting between two turns in a motor. DETAILED DESCRIPTION

[0019] Figure 1 Schematically and partially representing an assembly according to an embodiment of the invention, the assembly comprises an electric machine 1000 and a device for detecting a short circuit between at least two turns of a winding of a phase of the machine 1000 .

[0020] The electric machine 1000 comprises three phases 100 , 200 and 300 .

[0021] The first phase 100 comprises two electrical paths 101 and 102. Each path 101 and 102 comprises a winding 111, 112. When entering the phase 100, the current I101+I102 circulates, then in the first path 101, the current I101 circulates, and in the second path 102, the current I102 circulates.

[0022] As with the first phase 100, the second phase 200 and the third phase 300 also include two electrical paths 201, 202 and 301, 302. As with the first phase 100, upon entering the phases 200 and 300, the current circulates and then splits between the two paths 201, 202 and between 301, 302 of the two phases 200 and 300. Therefore, the current I201 circulates in the path 201, the current I202 circulates in the path 202, the current I301 circulates in the path 301, and the current I302 circulates in the path 302.

[0023] Each first electrical path 101 , 201 , 301 of the three phases 100 , 200 , 300 is connected to the same electrical node 10 , and each second electrical path 102 , 202 , 302 of the three phases 100 , 200 , 300 is connected to the same electrical node 20 .

[0024] The electric machine 1000 further includes an equipotential line 400 electrically connecting the first electrical node 10 and the second electrical node 20. The machine 1000 includes a current sensor 500 configured to measure currents (I101+I201+I301)-(I102+I202+I302) that can circulate in the equipotential line 400.

[0025] The detection of a short circuit in an operating motor is based on the measurement of the current in the equipotential conductor 400 by a current sensor 500. According to the invention, the current measurement value of the sensor 500 is compared with a predetermined detection threshold value, which is at least equal to twice the value of the residual current I that can be measured in the absence of any electrical fault.

[0026] The detection of a short-circuit fault makes it possible to safely protect the motor 1000 , for example by short-circuiting all phases 100 , 200 , 300 to reduce the short-circuit current between the turns and / or shutting down the motor by mechanically disconnecting the rotor.

[0027] Under 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 the same value of magnetic flux at any time, which is the convention for parallel connection. Therefore, the current (I101+I201+I301)-(I102+I202+I302) circulating in the equipotential line 400 is zero or almost zero, and there may be a residual current or noise current. This residual current is actually less than 5% of the nominal current of the motor 1000. Therefore, under normal operation of the motor 1000, the current (I101+I201+I301)-(I102+I202+I302) measured by the single current sensor 500 is zero, or almost zero.

[0028] If a short circuit occurs between the turns of one of the windings 111 , 112 , 211 , 212 , 311 , 312 , the current ( I101 + I201 + I301 )−( I102 + I202 + I302 ) measured by the current sensor 500 will no longer be zero, and the increase in the current measured by the sensor 500 makes it possible to detect the short circuit.

[0029] For example, if a short circuit occurs between the turns of one of the windings 111, 112 of the first phase 110, a non-zero circulating current I101-I102 occurs between the paths 101 and 102. Figure 1 The current (I101+I201+I301)-(I102+I202+I302) measured by the sensor 500 is equal to I101-I102. Comparing the current measured by the sensor with the detection threshold makes it possible to detect a short circuit fault and, if applicable, to safely protect the motor.

[0030] This detection according to the invention is done via the addition of a single equipotential wire 400 and a single current sensor 500 measuring the current circulating in this wire 400 and by comparison based on a detection threshold determined relative to the residual current measurable in the wire 400 in the absence of any electrical fault (which is at least twice greater than this residual current, ensuring reliable detection). Thus, the equipotential wire 400 and the current sensor 500 form means for detecting a short circuit between at least two turns of a winding of a phase of the electric machine 1000.

[0031] Since the motor 1000 has N turns per phase, a short circuit between two turns in the electrical path appears as an imbalance in the number of turns in the ratio of 1 / N. When the number of turns per phase is low, the current in the equipotential line 400 will be high when a fault occurs. Therefore, the present invention is particularly suitable for machines where the number of turns per phase N is not very high (e.g., less than or equal to 50).

[0032] For example, and refer to Figure 1 , if the windings of the electrical paths of the phases each comprise 20 turns, then in the event of a short circuit between two turns of one of these windings, the electrical path in question will have no more than 19 turns, and therefore an unbalance of 5% in the number of turns. The induced voltages in the two parallel paths will therefore be different simply due to the difference in the number of turns, while the magnetic flux in the path with the fault will itself be reduced by the influence of the current in the short-circuited turns, according to Lenz's law. The circulating current measured by the current sensor is therefore significantly higher than the residual current determined under normal operation, which makes it possible to set the detection threshold of the short-circuit fault to at least twice the residual current determined by the motor, a factor of two constituting a sufficient margin with respect to the residual current, since it can be assumed that if the current exceeds this threshold, a confirmed fault is indeed present.

[0033] Figure 2 Schematically showing a method for detecting a motor of the present invention (for example, Figure 1 A method 2000 for short-circuiting two turns of the motor 1000).

[0034] The method 2000 comprises: measuring 2010 a current I circulating in the equipotential line 400 mesure (or according to Figure 1 The current (I101+I201+I301)-(I102+I202+I302)) determines the residual current I20 circulating in the equipotential line 400 residuel , and when I mesure isI residuel In other words, the detection threshold is at least equal to I residuel twice as much.

[0035] Current I residuel corresponds to the residual noise circulating in the equipotential line 400 under normal operation of the motor 1000, and as referenced Figure 1 As explained, in any case, the residual current I residuel is zero or almost zero and is on average less than 5% of the nominal current in the motor 1000. This residual current is a measurable characteristic of the motor under consideration. In particular, this I residuel (Step 2020). The value I determined for the prototype residuel is the value of the motor corresponding to this prototype residuel In one variant, provision may be made to measure the I residuel In other words, the residual current I can be determined at the factory residuel .

[0036] Different embodiments of the detection, in particular the comparison of the current measurement signal provided by the sensor with a defined detection threshold, can be envisaged using any hardware or software technique known to a person skilled in the art. In the case of a software embodiment, the residual current measured for the motor (during the testing of a prototype or of the machine itself) is a parameter of the machine, which is stored, for example, in a memory of the control device of the motor or in a memory in a registry. In the case of a hardware embodiment, the comparison circuit is designed to ensure the detection of a current above a defined detection threshold which is greater than at least twice the residual current determined for the motor under consideration.

[0037] Whatever the embodiment, the electrical machine 1000 may also comprise a fuse device configured to limit the heating of the equipotential wire 400 in the event of a short circuit in a phase 100 , 200 , 300 of the electrical machine.

[0038] Electric machine 1000 is described as having three phases, but it may more generally include N phases, where N is an integer greater than or equal to one.

Claims

1. An assembly comprising: an electric machine (1000), the electric machine comprising at least one phase (100, 200, 300), the at least one phase comprising two electrical paths (101, 102, 201, 202, 301, 302) connected in parallel, each electrical path of the same phase comprising 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 a device for detecting a short circuit between at least two turns of a winding of a phase, characterized in that The motor comprises an equipotential line (400) and a current sensor (500), the equipotential line electrically connecting the first electrical node and the second electrical node, the current sensor being configured to measure a current (I101+I201+I301-(I102+I202+I302)) circulating in the equipotential line, and a detection device being configured to compare the current measured by the current sensor with a detection threshold, the detection threshold being equal to a residual current (I101+I201+I301-(I102+I202+I302)) circulating in the equipotential line in the absence of any short circuit between turns of the winding. residuel ) at least twice.

2. The assembly according to claim 1, wherein The current sensor is a current transformer, and the equipotential line is placed at the center of the current transformer.

3. A method (2000) for detecting a short circuit in an electric machine according to any one of claims 1 and 2, comprising: The current (I) circulating in the equipotential line was measured (2010). mesure ), determine (2020) the residual current (I residuel ), and if the measured current (I mesure ) becomes greater than a detection threshold, a short circuit is detected (2030), the detection threshold being equal to the determined residual current (I residuel ) at least twice.

4. The detection method according to claim 3, wherein: The residual current is determined at the factory.

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