DE102019107725A1 - Apparatus and a method for detecting a shorted winding in a stator coil - Google Patents

Abstract

The present invention relates to an evaluation device and a method for detecting a shorted winding in a stator coil (10) of an electrical machine, the evaluation device having a wire loop (20) and an evaluation circuit (30) for detecting the voltage Uind induced in the wire loop (20), the wire loop (20) being wound around the stator coil (10), the stator coil (10) forming two measuring connections (M1, M2) at the end, to which two input connections (SENS1, SENS2) of the evaluation circuit (30) are connected and where the evaluation circuit (30) has at least one operational amplifier (OP) for amplifying the voltage signal, a comparator (K) for comparing the detected voltage signal with a reference signal and a flip-flop IC (IC) for evaluating the result of the comparator (K), to generate a signal when the induced voltage Uind detected in the wire loop (20) by a predetermined factor r k is smaller than a target limit value of a target reference voltage Usoll.

Description

The invention relates to a device and a method for detecting a shorted winding of a stator coil, in particular a stator coil of a rotating field machine.

Interturn faults can occur in the coils of electrical machines in both the stator and rotor windings. An electrical short circuit between two or more turns of a stator winding is to be understood as a winding short circuit or winding short circuit in a stator winding.

A number of diagnostic functions are required for monitoring and troubleshooting electrical drives that have an electric machine. As a rule, short circuits to ground and supply are detected. The detection of a shorted winding in the coils of the electrical machine is possible in principle by measuring the ohmic resistance at the phases of the electrical machine. However, this resistance is generally very small, so that line impedances or transition resistances at (plug) connections can falsify the measurement result and are therefore inaccurate. Furthermore, if a (partial) short circuit occurs between two phases or within the phase of the electrical machine, this is often not or at least not clearly detected.

From the EP 1 312 929 A1 a method for monitoring electrical insulation of a rotor of an electrical machine is known. A magnetic field of two coils, which are connected in series with a rotor winding, is recorded. A change in the magnetic field of the two coils can indicate a change in the state of the insulation, such as a winding short.

From the DE 10 2008 017 900 A1 a method for detecting a fault in an induction machine is known. Here, a flux-forming current component is subjected to a frequency analysis.

From the DE 10 2009 004 556 A1 it is known that in a PWM-controlled electric machine, partial winding faults can be detected by observing a current ripple resulting from the PWM voltage switching.

Another solution for the detection of short turns in the rotor winding is for example from the DE 10 2009 003 549 A1 known. A search coil is used, which is arranged in the air gap in the immediate vicinity of the surface of the rotor. Short turns in the alternating current windings of the stator can be recognized by asymmetries in the electrical currents of different winding phases or winding branches connected in parallel. However, this has the disadvantage that other deviations from the ideal state of the electrical machine, such as out-of-roundness of the stator, can also lead to such asymmetries. This makes it very difficult to separate the two effects in this way.

Another known method for detecting shorted turns in the stator uses flux measuring coils, the two coil legs of which are guided in the slot closure wedges of two slots and thus cover a certain area of the stator core in the circumferential direction. A disadvantage of this method is that these measuring coils can only be built into an existing machine with considerable effort.

Further disadvantages of known methods can be seen in the fact that winding faults and shorted turns can only be detected with sufficient reliability from a share of approx. 10% of the complete winding. However, it would be desirable to have a detection in the event of a single coil short between two coil wires.

The invention is therefore based on the object of overcoming the aforementioned disadvantages and of providing a simple and cost-effective solution for the detection of winding shorts.

The object is achieved according to the invention by the features of claim 1.

A basic idea of the present invention relates to the utilization of the effect of the change in the stray field due to a winding short and its evaluation with an evaluation circuit.

According to the invention, an evaluation device for detecting a shorted winding in a stator coil of an electrical machine is proposed for this purpose, the evaluation device having a wire loop and an evaluation circuit for detecting the voltage U _ind induced in the wire loop, the wire loop being wound around the stator coil, the stator coil Forms two measuring connections at the end, with which two input connections of the evaluation circuit are connected and wherein the evaluation circuit has at least one operational amplifier for amplifying the voltage signal, a comparator for comparing the detected voltage signal with a reference signal (setpoint signal) and a flip-flop IC for evaluating the result of the Comparator has to a signal generate, if the wire loop in the detected induced voltage U _ind k by a predetermined factor is less than a desired limit of a target reference voltage U _soll.

In an advantageous embodiment it is further provided that an LED is also provided in the evaluation circuit, which lights up, in particular lights up continuously, when the induced voltage U _{ind falls below} the setpoint limit value. From this, a shorted turn can be recognized optically by a person during operation of the electrical machine.

In a preferred and advantageous embodiment of the evaluation device it is provided that the output of the comparator is connected to an input of the flip-flop IC in order to be able to evaluate the result of the comparator directly. The evaluation can alternatively z. B. also be done by means of a microcontroller.

Another preferred embodiment of the evaluation device provides that an input of the operational amplifier is connected to one of the ends of the wire loop. When monitoring a large number of stator coils with an evaluation device, it would also be conceivable that the ends of the respective coils are connected to the inputs of a single evaluation circuit so that they can be separated and connected via a switching device, so that only the coil that is currently active with the can be monitored Evaluation circuit is connected while the separate wire loops are inactive. In this way, an inexpensive evaluation device can be provided that monitors a large number of stator coils.

In a particularly advantageous embodiment of the evaluation circuit, it is provided that the factor k> 1.5, preferably greater than 2. This makes it possible to clearly detect a shorted turn and distinguish it from any voltage ripples that may occur.

Another aspect of the present invention relates to a method for detecting a shorted winding in a stator coil of an electrical machine, in which the stator coil has two connections and an electrical alternating voltage is applied via these, a wire loop being wound around the stator coil to be monitored, which Forms two measurement connections at the end, which are connected to an evaluation circuit for detecting the voltage U _ind induced in the wire loop, the evaluation circuit being designed to detect a shorted winding in the stator coil on the basis of the level or the peak values of the currently detected induced voltage U _ind . This takes place in that the evaluation circuit is designed as described above or, alternatively, is designed in such a way that a target / actual value comparison, preferably over a longer period of time, of the peak values of the current induced voltages to the induced voltage in the error-free state (i.e. without a shorted turn) the turns is carried out.

The method is also advantageous if the evaluation circuit is used to generate a quotient between the target reference voltage U _soll , which corresponds to the induced voltage in the wire loop in the absence of a winding short in a stator coil, and the induced voltage U _ind currently detected in the wire loop and It is evaluated whether this quotient is greater or less than a predetermined factor k and, depending on this, a conclusion is drawn as to the presence or absence of an interturn fault.

Furthermore, it can be provided that a comparison table is stored in a system memory in which each k-value is assigned its magnitude according to the extent of a shorted turn. For example, with a factor of k = 1.5, only two turns could be short-circuited, while with a factor of k = 6, 20% of the turns already have a short circuit. In this way, the actually recorded factor k can be used to infer not only the basic presence, but also the extent to which a coil short is present.

It is particularly advantageous in the idea of the invention that the method can be carried out on a stator coil of an electrical machine during operation of the electrical machine. This enables continuous operational monitoring and early detection of problems with shorts in the winding.

Another aspect of the present invention relates to an electrical machine, in particular an electrical induction machine having an evaluation device as described above.

Other advantageous developments of the invention are characterized in the subclaims or are shown in more detail below together with the description of the preferred embodiment of the invention with reference to the figures.

• 1 eine schematische Ansicht einer Statorspule mit einer Drahtschlaufe ausgebildet als Messwicklung;
• 2 eine Auswerteschaltung gemäß einer beispielhaften Ausführungsform und
• 3 eine Messkurve der induzierten Spannungen mit und ohne Windungsschluss.

It shows:

• 1 a schematic view of a stator coil with a wire loop designed as a measuring winding;
• 2 an evaluation circuit according to an exemplary embodiment and
• 3 a measurement curve of the induced voltages with and without interturn shortfalls.

In the following the invention with reference to the 1 to 3 explained in more detail, with the same reference symbols in the figures indicating the same functional and / or structural features.

In the 1 Figure 3 is a schematic view of a stator tooth 2 with a stator coil 10 shown. The stator coil 10 has two connections ( 10a , 10b ) to the stator coil 10 to energize. Around the stator coil 10 is a wire loop 20th designed as a measuring winding. The stator coil forms10 two measuring connections at the end M1 , M2 that is used to connect to the in the 2 evaluation circuit shown 30th are provided.

The 2 shows an evaluation circuit only as an example 30th according to an embodiment of the invention. The evaluation circuit 30th can also alternatively be implemented with the same basic functions, with the proposed evaluation circuit 30th represents a particularly efficient and inexpensive variant. The evaluation circuit 30th includes, inter alia, conventional electronic components, such as resistors R, capacitors C, switches S, which do not require any further explanation and must be adapted accordingly to the application. The connection 31 is connected to the earth potential GND.

The evaluation circuit 30th and the wire loop 20th together form an evaluation device. The ones in the 2 Evaluation circuit shown 30th has two connectors 31 , 32 to apply a voltage, the connection 32 a connection for a reference voltage level forms z. B. for a 5V voltage which is fed to a comparator K of the circuit.

The wire loop 20th with their connection-side ends M1 , M2 at the two input connections SENS1, SENS2 of the evaluation circuit 30th connected. The evaluation circuit 30th also has an operational amplifier OP for amplifying the induced voltage signal from the wire loop 20th , which is fed to an input of the comparator K.

After comparing the detected voltage signal with the reference signal, the output signal of the comparator K is fed to a flip-flop IC. An output of the flip-flop IC is also connected to an LED D1, which lights up continuously when the induced voltage U _{ind falls below} the setpoint limit value, as long as the measurement takes place.

The 3 shows a measurement curve of the induced voltages U _ind with and without interturn short-circuit, the solid curve representing the case in which there is no interturn short-circuit. The ordinate here represents an exemplary dimensionless value for the voltage amplitudes and peak values of the measured induced voltages U _ind , which in the undisturbed case (without interturn short-circuit) is approximately 6.5. If there is an interturn fault, this peak value drops to approximately 2.5. Thus a factor K of 2.6 would be obtained.

An automatic shutdown of the engine via an electrical shutdown device, such as. B. a relay would also be beneficial.

QUOTES INCLUDED IN THE DESCRIPTION

This list of the documents listed by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent literature cited

• EP 1312929 A1 [0004]
• DE 102008017900 A1 [0005]
• DE 102009004556 A1 [0006]
• DE 102009003549 A1 [0007]

Claims (10)

Evaluation device for detecting a shorted winding in a stator coil (10) of an electrical machine, the evaluation device having a wire loop (20) and an evaluation circuit (30) for detecting the voltage U _ind induced in the wire loop (20), the wire loop (20) is wound around the stator coil (10), the stator coil (10) forming two measuring connections (M1, M2) at the end, to which two input connections (SENS1, SENS2) of the evaluation circuit (30) are connected and the evaluation circuit (30) at least an operational amplifier (OP) for amplifying the voltage signal, a comparator (K) for comparing the detected voltage signal with a reference signal and a flip-flop IC (IC) for evaluating the result of the comparator (K) in order to generate a signal, when the induced voltage U _ind detected in the wire loop (20) is smaller by a predetermined factor k than a setpoint limit value of a setpoint Ref erential voltage U _soll . Evaluation device according to Claim 1 , characterized in that an LED (D1) is also provided in the evaluation circuit (30), which lights up, in particular lights up permanently, when the induced voltage U _{ind falls below} the setpoint limit value. Evaluation device according to Claim 1 or 2 , characterized in that the output of the comparator (K) is connected to an input of the flip-flop IC (IC). Evaluation device according to one of the preceding Claims 1 to 3 , characterized in that an input of the operational amplifier (O) is connected to one of the ends (M1, M2) of the wire loop (20). Evaluation device according to one of the preceding claims, characterized in that the factor k> 1.5, preferably greater than 2. Method for the detection of a shorted winding in a stator coil (10) of an electrical machine, in which the stator coil (10) has connections (11) and an alternating voltage is applied through them, characterized in that a wire loop around the stator coil (10) (20) is wound, which forms two measuring connections (M1, M2) at the end, which are connected to an evaluation circuit (30) for detecting the voltage U _ind induced in the wire loop (20), the evaluation circuit (30) being formed To detect a shorted winding in the stator coil (10) based on the level of the currently detected induced voltage U _ind . Procedure according to Claim 6 , whereby a plurality of successive peak values of the induced voltage U _{ind are determined} over a certain period of time. Procedure according to Claim 6 or 7th , with the evaluation circuit (30) a quotient between the target reference voltage U _soll , which corresponds to the induced voltage in the wire loop (20) in the absence of a short-circuit in a stator coil (10) and which is currently detected in the wire loop (20) induced voltage U _{ind is} formed and it is evaluated whether this quotient is greater or less than a predetermined factor k and, depending on this, the existence or non-existence of an interturn short is inferred. Method according to one of the Claims 6 to 8th , the method being carried out on a stator coil (10) of an electrical machine during operation of the electrical machine. Electrical machine, in particular electrical induction machine, comprising an evaluation device according to one of the Claims 1 to 6th .

Images