WO2009127562A2

WO2009127562A2 - Method for monitoring an electrodynamic motor

Info

Publication number: WO2009127562A2
Application number: PCT/EP2009/054192
Authority: WO
Inventors: Max Hobelsberger
Original assignee: Alstom Technology Ltd
Priority date: 2008-04-15
Filing date: 2009-04-08
Publication date: 2009-10-22
Also published as: DE102008001183A1; WO2009127562A3

Abstract

The invention relates to a method for monitoring an electrodynamic motor comprising a rotor arrangement (11) which is rotatably mounted in a stator (12). According to said method, at least one measuring variable depending on a magnetic field generated by the electrodynamic motor is detected and evaluated in order to analyse mechanical, electrical and/or magnetic properties of the rotor arrangement (11). The invention is characterised in that the at least one measuring variable is detected on or outside a surface of the stator (12), facing away from the rotor arrangement (11), by means of a sensor.

Description

Method for monitoring an electrodynamic machine

Technical area

The invention relates to a method for monitoring an electrodynamic machine which has a rotor assembly rotatably mounted within a stator, in which at least one measured variable is detected and evaluated by one of for evaluating mechanical, electrical and / or magnetic properties of the rotor assembly depends on the electrodynamic machine generated magnetic field.

PRIOR ART Electrodynamic machines convert mechanical energy into electrical energy (generator operation) or electrical energy into mechanical energy (electric motor operation). The transformation is based on the Lorentz force, which acts on moving charges in a magnetic field.

In the following, by way of example, without wishing to make a restriction, on electrodynamic machines that work as generators, received. In particular, the statements relate to large-scale plants, for example, large synchronous generators as they are used, inter alia, in industrial power generation.

The generator consists of a mounted on a rotary axis rotor which rotates within a fixed stator with a rotor rotation frequency. The rotor generates a circulating direct magnetic field during rotation, which induces a sinusoidal electrical voltage and thus a sinusoidal current in the stator windings. The DC field of the rotor is generated by current-carrying windings, which are arranged in grooves which extend parallel to the axis of rotation. The windings exist in large-scale systems, for example, hollow metal bands whose outer surfaces are electrically insulated from each other by means of a plastic layer. Inside the hollow metal bands circulates mostly a cooling medium.

During operation, high mechanical forces act on the rotor windings, due to the centrifugal forces, as well as thermal stresses due to ohmic heat, which can lead to mechanical deformations. Under unfavorable conditions, such deformations lead to the insulation layer of the windings being locally damaged so that so-called rotor winding closures can occur. These in turn cause the rotor to heat unevenly, which leads to uneven deformation of the rotor and thus to imbalances and vibrations of the rotor assembly and shaft assembly. If the vibrations are too great, the machine must be switched off to prevent damage to the machine.

Another cause of vibration may also be non-uniform pole arrangements of the magnetic field generated by the rotor.

Electrodynamic machines, in particular large generators, are therefore monitored during operation in order, for example, to recognize rotor winding connections or vibrations at an early stage and thus to be able to avoid damage to the machine.

An example of a method known from US 3,506,914 for the detection of rotor windings is the so-called stray field measurement, in which by means of air gap sensors, which are mounted in the air gap between the rotor and stator, the magnetic stray field generated by the rotor tangential to the rotor surface is measured. It is exploited that Windungsschlüsse cause measurable in the air gap modification of the stray field.

The monitoring by means of air gap sensors, however, has some disadvantages. Due to the mechanical exposure of the sensors, there is the risk of damaging the air gap sensors, in particular if the rotors are removed, maintained and reused at certain time intervals. In addition, measuring techniques are used with which diagnostic measurements in the air gap can be carried out with built-in rotor by means of movable probes. This can lead to damage of the air gap sensors by the diagnostic probes or to hinder the diagnosis measurement by the air gap sensors.

Another disadvantage lies in the considerable constructive, and associated financial expense, which must be operated for wiring, seals, etc. This is particularly serious with turbogenerator types that are filled with pressurized hydrogen gas for cooling purposes. In these cases, particularly expensive gas-tight bushings are necessary. In addition, the air gap sensor and its signal lines are in the high voltage range of the generator, which requires further measures to reduce the operating risk.

An additional disadvantage of these air gap sensors is that repairs to the sensor during operation of the machine are usually not possible. Usually, this requires the rotor to be exposed to reach the defective sensor or signal cable.

In addition to the above-described stray field measurement in the air gap between the rotor and the stator, the measurement of the magnetic field is also described in an article by Prof. Simond: "Unbalanced Magnetic Pull and Air Gap Monitoring for Large Hydrogenators", UMP-Monitoring / EPF-Lausanne, Dec.2004 Another disadvantage in this case is that the required sensors are not or are not easily accessible during operation, Again, special, for example due to the hydrogen filling pressure-resistant and gas- Dense housing bushings needed. Furthermore, in the case of mechanical defects, the sensor parts can get into the ventilation channels of the machine, for example, and endanger the operation. The elimination of these disadvantages requires additional, not insignificant financial efforts.

Presentation of the invention

The invention is based on the object to provide a method for monitoring an electrodynamic machine, which has a rotor assembly rotatably mounted within a rotor, in which for the assessment of mechanical, e- lectric and / or magnetic properties of the rotor assembly detected and evaluated at least one measure which depends on a magnetic field generated by the electrodynamic machine. In particular, the method should be able to obtain useful information about the main magnetic field of the electrodynamic machine in a cost-effective, low-maintenance and harmless manner.

The solution of the problem underlying the invention is specified in claim 1. The solution according to the method for monitoring an electrodynamic machine advantageously further-forming features are the subject of the dependent claims and the further description, in particular with reference to the embodiment, refer.

According to the solution, the method for monitoring an electrodynamic machine according to the features of the preamble of claim 1 is characterized in that the at least one measured variable is sensed on or outside a surface of the stator facing away from the rotor assembly.

Electrodynamic machines, especially large power plant generators, have a pronounced stray magnetic field on the outer surface of the machine. This stray magnetic field is generated by the main magnetic field generated by the current flow in the rotor windings according to the magnetic scattering field. laws and is structurally closely related. The field exit is typically perpendicular to the metallic surface of the machine. By short circuit currents, which revolve, for example, in the tie rod constructions on the outside of the laminated core of the stator assembly, the field is modified. Because of the vertical orientation, the stray field also penetrates the steel housing which normally encloses the generator, with eddy currents in the housing again causing a modification of the field.

So far, it has been assumed that meaningful measured values, for example for the detection of windings, can be obtained in the air gap, above all by magnetic field measurements, where, on the one hand, there is a sufficient signal-to-noise ratio and, on the other hand, a direct assignment of the measured value and condition of the windings ,

According to the invention, it has been recognized that important structural characteristics of the main field generated by the machine and the air gap field are not only measurable in the air gap, but are also recognizable in modified form in the stray field, on or outside the surface of the electrodynamic machine, for example on the outer surface of the electrodynamic machine Statorblechpakets, the so-called "plate back", or even on the outer surface of the housing, can be measured.

Rotor windings, vibrations of the rotor, in particular torsional vibrations and / or magnetically nonuniform pole arrangements of the rotor arrangement are preferably detected by the method, which lead to changed mechanical, electrical and / or magnetic properties of the rotor arrangement. Here, the measurement according to the invention of the at least one measured variable on or outside a surface of the stator facing away from the rotor assembly replaces the measurement of the magnetic field in the air gap. Thus, the serious disadvantages associated with the air gap measurement, such as mechanical exposure of the sensors, inaccessibility of the sensors during operation, additional design effort or elaborate seals and bushings, can be avoided. In addition, both permanent and continuous monitoring by means of permanently installed sensors can be realized with the method according to the solution. However, it is equally possible to carry out a diagnosis with a mobile measuring device.

Particularly preferred is a method in which the magnetic field itself is detected by means of a magnetic field-sensitive sensor in the manner of a coil, a conductor loop, a Hall sensor or a magnetoresistive sensor. In this case, the magnetic-field-sensitive sensor is preferably mounted on the surface of the stator or on the outside of the housing.

In a further preferred embodiment, a plurality of magnetic-field-sensitive sensors, for example at the same circumferential distance, are arranged outside the stator. In this case, the symmetrical arrangement allows additional diagnostic options such as the investigation of the pure rotational components of the field.

In particular, the spectrum of the stray field, that is, the magnetic field as a function of frequency is examined, the spectrum of the stray field information on the spectrum of the air gap field can be removed. It is particularly preferred that the at least one sensory measured variable is analyzed in the frequency domain.

Preferably, an amplitude spectrum and / or a phase spectrum is created and analyzed on the basis of the at least one sensory measured variable. In the context of the analysis, the amplitude spectrum and / or the phase spectrum are preferably evaluated by comparison with a desired amplitude spectrum or desired phase spectrum, which corresponds to a reference operating state of the rotor arrangement. In particular, increased levels in the amplitude or phase spectrum in comparison to the respective desired spectrum indicate a disturbance in the rotor arrangement. For detection of rotor winding terminals, the amplitude or the phase spectrum can be analyzed. In particular, increased levels in the amplitude spectrum, which occur in particular in each case at even multiples of the rotor rotational frequency, indicate rotor winding closures. It should be noted that in the desired amplitude spectrum corresponding to the trouble-free operation, no or only relatively small even multiples should be recognized, at least when the influence of the phase currents of the machine and the influence of the originating from the network even field harmonics are corrected , If then even multiples occur in the spectrum, this is an indication of Rotorwindungsschlüsse.

Increased levels in the amplitude spectrum can in particular also indicate magnetically uneven pole arrangements of the rotor and thus field distortions. In contrast to the spectrum for rotor winding connections, however, the entire spectrum is changed.

Information about the presence of vibrations of the rotor arrangement, in particular in the form of torsional vibrations, can preferably also be taken from the amplitude or phase spectrum. Here, a widening of spectral lines in the amplitude spectrum and / or in the phase spectrum in comparison to the desired amplitude spectrum or desired phase spectrum indicates the presence of unwanted vibrations. In particular, the spectral lines of the rotor frequency and / or their harmonics and / or secondary lines of the rotor frequency and / or their harmonics are investigated.

In another preferred embodiment of the method, the at least one sensory measured variable is analyzed in the time domain. In this case, it is particularly preferred that the sensory measured variable is differentiated in time and / or filtered. Particularly preferred embodiments of the method are characterized in that an influence of phase currents of the electrodynamic machine is compensated to increase the measurement accuracy when evaluating the at least one measured variable. In particular, the phase currents of the machine are measured and suitably added or subtracted to the detected measurement signals, for example the field coils. Underlying this is the realization that the main field and thus also the external stray field are generated by the common magnetic effect of stator current and rotor current. In particular, there is the possibility to reduce the influence of originating from the network even multiple of the rotor rotation frequency in the spectrum.

Furthermore, it is preferred that in the method an axial and / or a tangential component of the magnetic field be detected and evaluated separately. The axial component runs parallel to the rotor axis of rotation. The tangential component lies in a plane perpendicular to the rotor axis of rotation and tangent to the surface. Here, in particular, a sensor is aligned in successive measurements each time so that either the axial or the tangential component is detected. In the case of a plurality of sensors, the detection of the axial or tangential component can take place simultaneously by appropriate alignment of the sensors.

In addition, it is particularly preferred that at least one sensor is used to detect the magnetic field, which generates a measurement signal representing the measured variable, which is subjected to preamplification and / or filtering. It is also preferred that the measurement signal is transmitted wirelessly, for example via a radio link, for evaluation or further processing. Of course, the transmission of the measured data can also be done via cable.

A further preferred embodiment of the method is characterized in that the at least one sensor acquires the electrical energy required for the sensor operation from the magnetic field generated by the electrodynamic machine, so that the sensor can be used completely autonomously. Instead of the direct detection of the magnetic field, loop currents induced by the stray field, for example in the tensile bars of the laminated stator core or else in foundation circuits of the iron armor or grounding circuits, can also be detected, which also contain structural features of the magnetic machine field. For this purpose, appropriate sensors are mounted at suitable locations, such as on the earthing rails.

Brief description of the invention

The invention will now be described by way of example without limitation of the general inventive idea by means of embodiments with reference to the drawings. Show it:

Fig. 1 shows a schematic section through a generator with attached outside of the air gap sensors and

Fig. 2 shows a schematic section through a generator with conventional

Air gap sensor according to the prior art

Ways to carry out the invention

FIG. 1 shows a schematic cross section through a generator arrangement 1. The sectional view oriented perpendicular to the rotor axis of rotation 14 shows a generator 1 resting on a foundation 5 and comprising a rotor 1 1, a stator 12 and a housing 13. The rotor 1 1 is rotatably mounted within the stator 12 about the rotor axis of rotation 14 and closes with the stator 12 an air gap 17 a. The magnetic stray field outside the generator arrangement 1 is detected by means of three magnetic field sensors 19, 20, 21 mounted outside the stator housing 13. Figure 2 represents as it were a cross section through the generator assembly 1 with further details for magnetic field generation. The rotor 11 is rotatably mounted in the stator 12 on a rotation axis 14. The rotor 1 1 has in rotor 15 extending current-carrying rotor windings 16 which generate the magnetic main field 2. The course of the magnetic field lines of the main field 2 is illustrated by arrows within the rotor 11, the air gap 17 and by the dashed lines in the stator 12. In addition to the main field 2, the field lines emerge substantially orthogonal to the rotor surface, formed in the air gap 17 an air gap scatter field 3 with tangential to the rotor surface field components, which is measured in the usual measurements with so-called air gap sensors 18. The reference numeral 4 refers to the stray field occurring outside of the generator 1, which is to be detected with the aid of the magnetic field sensors 19, 20, 21 illustrated in FIG. 1 and evaluated accordingly.

LIST OF REFERENCE NUMBERS

generator

main field

Air gap field

stray field

foundation

rotor

stator

casing

Rotor axis of rotation

groove

rotor windings

air gap

Air gap sensor magnetic field sensor

Claims

claims

1. A method for monitoring an electrodynamic machine having a rotatably mounted within a stator (12) rotor assembly (1 1), wherein for the assessment of mechanical, electrical and / or magnetic properties of the rotor assembly (1 1) detects at least one measured variable and is evaluated, which depends on a magnetic field generated by the electrodynamic machine, characterized in that the at least one measured variable on or outside of the rotor assembly (1 1) facing away from the surface of the stator (12) is detected by sensors.

2. The method according to claim 1, characterized in that are detected as mechanical, electrical and / or magnetic properties rotor windings, vibrations of the rotor, in particular Tor- sionalvibrationen, and / or magnetically non-uniform polar arrangements of the rotor assembly (1 1).

3. The method according to claim 1, characterized in that for detecting the magnetic field-dependent measured variable, a magnetic field-sensitive sensor (19, 20, 21) in the manner of a coil, a conductor loop, a Hall sensor or a magnetoresistive sensor is used.

4. The method according to claim 3, characterized in that a plurality of magnetic field-sensitive sensors (19, 20, 21) are arranged around the stator (12).

5. The method according to any one of claims 1 to 4, characterized in that the at least one sensory detected measured variable is analyzed in the frequency domain.

6. The method according to any one of claims 1 to 5, characterized in that on the basis of the at least one sensory measured variable, an amplitude spectrum and / or a phase spectrum are created and analyzed.

7. The method according to claim 6, characterized in that the amplitude spectrum and / or the phase spectrum are evaluated by comparison with a desired amplitude spectrum or desired phase spectrum corresponding to a reference operating state of the rotor assembly (1 1).

8. The method of claim 2 and 7, characterized in that for the determination of rotor windings in the amplitude spectrum increased levels are determined in each case even multiples of a rotor rotation frequency.

9. The method according to claim 2 and 6 or 7, characterized in that the phase spectrum is analyzed for the determination of rotor windings.

10. The method according to claim 6 or 7, characterized in that for determining magnetically non-uniform pole arrangements of the rotor (1 1) increased levels in the amplitude spectrum can be determined.

1 1. A method according to any one of claims 5 to 7, characterized in that for determining vibrations of the rotor assembly (1 1), in particular in the form of Torsionalvibrationen, a broadening of spectral lines in the amplitude spectrum and / or in the phase spectrum is used.

12. The method according to claim 1 1, characterized in that the spectral lines of the rotor rotational frequency and / or their harmonics and / or secondary lines of the rotor rotational frequency and / or their harmonics are examined.

13. The method according to any one of claims 1 to 4, characterized in that the at least one sensory detected measured variable is analyzed in the time domain.

14. The method according to claim 13, characterized in that the sensory detected measured variable is time differentiated and / or filtered.

15. The method according to any one of claims 1 to 14, characterized in that when evaluating the at least one measured variable, an influence of phase currents of the electrodynamic machine is compensated.

16. The method according to any one of claims 1 to 15, characterized in that an axial and / or a tangential component of the magnetic field are detected and evaluated separately.

17. The method according to any one of claims 1 to 13, characterized in that for detecting the magnetic field, at least one sensor (19, 20, 21) is used, which generates a measuring signal representing the measured value, a pre-amplification and / or filtering is subjected.

18. The method according to claim 17, characterized in that the measurement signal is transmitted wirelessly for evaluation or further processing.

19. Method according to claim 3, characterized in that the at least one sensor (19, 20, 21) acquires an electrical energy required for the sensor operation from the magnetic field generated by the electrodynamic machine.