Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01H—MEASUREMENT OF MECHANICAL VIBRATIONS OR ULTRASONIC, SONIC OR INFRASONIC WAVES
  • G01H1/00—Measuring characteristics of vibrations in solids by using direct conduction to the detector
  • G01H1/003—Measuring characteristics of vibrations in solids by using direct conduction to the detector of rotating machines
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
  • G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
  • G01R31/34—Testing dynamo-electric machines
  • G01R31/343—Testing dynamo-electric machines in operation

Definitions

• the invention relates to a method for monitoring an electrodynamic machine, in particular a generator, having a rotor assembly mounted within a stator along a rotatable shaft and including an air gap with the stator in which at least one is disposed within the air gap or within the stator Sensor measurement signals are detected and evaluated, which depend on a magnetic field generated by the electrodynamic machine.
• 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.
• the embodiments relate to large-scale installations, e.g. large synchronous generators, such as those used in industrial power generation.
• the generator has a rotor mounted on a shaft which rotates within a fixed stator at a rotor rotational frequency.
• the rotor generates a circulating magnetic DC field, which in the stator windings produces a sinusoidal electrical voltage and thus a sinusoidal current induced.
• 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.
• Electrodynamic machines in particular large generators, are monitored during operation in order to be able to detect, in particular, vibrations of the shaft or their causes at an early stage and in order to avoid damage to the machine.
• the vibrations of the shaft preferably occur in the form of torsional vibrations, pendulum vibrations and / or bending vibrations.
• Torsional vibrations are vibrations that lead to a non-uniform rotational frequency along the shaft and thus to a torsion of the shaft. For example, they can be caused by sudden load changes.
• the torsional vibrations are very small vibrations, usually with a phase amplitude in the range of 0.01 °, but can still lead to a very high load on the shaft.
• the frequencies with which torsional vibrations occur depend on the nature of the material and the thickness of the shaft, the masses connected to the shaft and the size of the system.
• pendulum oscillations quasi-periodically damped changes in the rotational frequency of the shaft to the mains frequency are called, which are caused for example by shock-like interference from the network and also have a torsional effect on the shaft.
• pendulum oscillations result in significantly slower changes in the instantaneous angular velocity at which the shaft is rotating, or the instantaneous phase of the rotational motion, than the aforementioned torsional vibrations.
• a large-scale generator for industrial power generation which has a nominal rotor rotational frequency of typically 50 or 60 Hz
• Torsional vibrations with typical frequencies between 100 and 300 Hz and pendulum oscillations with typical frequencies of 5 to 10 Hz are examples of 5 to 10 Hz.
• vibrations may also be caused by rotor winding closures or may be due to non-uniform pole arrangements of the magnetic field generated by the rotor.
• US Pat. No. 3,506,914 discloses a method by which rotor windings can be detected which, as mentioned above, can lead to vibrations.
• the so-called stray field measurement is used, in which with the help of air gap sensors, which are mounted in the air gap between the rotor and stator, the rotor generated, running tangentially to the rotor surface magnetic stray field is measured. It is exploited that Windungs say cause measurable in the air gap modification of the stray field.
• JP 52110449 Another possibility for determining torsional vibrations along a generator shaft is described in JP 52110449. It is based on the measurement and evaluation of phase-terminal currents of the generator. This method is also relatively inaccurate and also requires current transformers for higher frequencies.
• the above-mentioned methods relate exclusively to the measurement of torsional vibrations, but not to the detection of bending vibrations.
• EP 1 537 390 B1 shows a method with which, in addition to torsional oscillations, pendulum and bending oscillations can also be detected. For this purpose, wave currents occurring on the shaft and / or shaft voltages outside the generator are tapped and evaluated.
• the invention is based on the object of developing a method for monitoring an electrodynamic machine, in particular a generator, in such a way that reliable detection of substantially all oscillation forms occurring along the shaft becomes possible. For this purpose, the most cost-effective and retrofittable even in already operating generators measures should be required.
• 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 developing features are the subject of the dependent claims and the further description in particular with reference to the embodiment refer.
• the method for monitoring an electrodynamic machine with a rotor assembly mounted within a stator along a rotatable shaft which includes an air gap with the stator, in which detected by at least one within the air gap (17) or within the stator sensor arranged measuring signals and are evaluated, which depend on a magnetic field generated by the electrodynamic machine, characterized in that the measurement signals obtained with the sensors arranged in the air gap or within the stator are used for detecting vibrations of the shaft.
• vibrations are, in particular, torsional vibrations, pendulum vibrations and / or bending vibrations.
• the measurement signals for determining the natural frequencies of the shaft oscillation are evaluated accordingly.
• the measurement signals to be evaluated are detected by already existing sensors, which are also provided for the detection of rotor windings.
• sensors preferably detect the tangential and / or radial magnetic field generated by the electrodynamic machine in the air gap between the rotor assembly and the stator.
• the main magnetic flux in the stator laminated core is also detected.
• Magnetic field-sensitive sensors are preferably used in the manner of a coil, a conductor loop, a Hall sensor or a magnetoresistive sensor.
• the sensory detected measurement signals are preferably detected in the time domain and / or in the frequency domain, for example by Fourier transformation of in the time domain Analyzes measured signals, wherein the detected measurement signals are evaluated at a nominal rotor rotational frequency and / or a multiple of the nominal rotor rotational frequency with respect to the phase, frequency and / or amplitude behavior.
• the detected measurement signals are examined with respect to frequency, phase and / or amplitude modulations contained therein. These can be seen in the spectrum as secondary lines of the nominal rotor rotational frequency or their harmonics or as broadening of the spectral lines belonging to the nominal rotor rotational frequency or its harmonics.
• the phase or frequency response is preferably analyzed by demodulation techniques known from radio technology. These include both analogous methods, e.g. Frequency shift methods or digital methods, e.g. Sampling method with temporally periodic sampling times.
• the detected measurement signals or signals derived therefrom are sampled at a sampling rate equal to the nominal rotor rotational frequency or an integer multiple, i. a harmonic, approximately equal to this frequency.
• the phase or frequency fluctuations of the detected measurement signals at the nominal rotor rotational frequency and / or the multiples of the nominal rotor rotational frequency are preferably determined based on a respective reference phase or reference frequency profile.
• the phase or frequency fluctuations of the detected measurement signals are subsequently used as a basis for evaluating the rotor rotational movement at nominal rotor rotational frequency and serve as a measure for the expression of the torsional vibrations and / or the pendulum oscillations of the shaft.
• the Referenzphasen- or frequency response is obtained from a reference signal having a larger phase constancy. Suitable is in particular a signal derived from the mains voltage.
• limit values for the phase or frequency fluctuations are specified. If exceeding the limit values is detected by the acquired measured values, a signal is generated or a shutdown of the electrodynamic machine is performed.
• the limits are determined for each frequency band, i. for the nominal rotor rotational frequency and its multiples, indicated and compared with the respective associated values of the phase fluctuation.
• determined amplitude fluctuations can be evaluated as a measure of bending vibrations in a suitable manner.
• several frequency bands of the detected measurement signals are simultaneously analyzed and examined for correlated amplitude fluctuations.
• a value for evaluating the rotor movement is determined exclusively on the basis of the correlated amplitude fluctuations.
• a limit value for the amplitude fluctuations is predetermined and, when the limit value is exceeded, a signal is generated or a switch-off of the electrodynamic machine is forced.
• an inductive air coil can be used as the sensor, which is acted upon by a higher-frequency current or voltage signal.
• this signal has a frequency above 500 Hz.
• the impedance fluctuations of the inductive air coil are evaluated.
• the sensor coil which occur for example due to eddy current losses or inductance changes, bending vibrations can be detected. This corresponds to the functional principle of an eddy current sensor.
• Particularly advantageous is the combination of field sensor and vibration sensor in a sensor head.
• the torsional, pendular and / or bending vibrations are detected, which are triggered by transient processes, for example by sudden load changes or shock-like disturbances in the network.
• the transient process manifests itself in a sudden change in the phase, frequency and / or amplitude behavior of the acquired measurement signals, in particular in transient phase, frequency and / or amplitude modulations.
• the excited torsional, pendular and / or bending vibrations cancel again after the transient excitation with characteristic time constants. From the information obtained during the excited state information about the phase, frequency and / or amplitude fluctuation, in particular from their spectra, it can be concluded on the torsional or Biegeschwingungs- natural frequencies of the wave. Above all, however, transient phase modulations that occur at harmonics of the nominal rotor rotational frequency indicate torsional vibrations of the shaft.
• the inventive method is used in particular for continuous monitoring of an electrodynamic machine.
• Fig. 1 shows a schematic section through a generator with a within the
• FIG. 1 shows a schematic section through a generator arrangement 1 for displaying details for magnetic field generation.
• the rotor 1 1 is rotatably mounted within the stator 12 on a shaft 10 along a rotational axis 14.
• the rotor 1 1 has in grooves 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 1 1, the air gap 17 and by the dashed lines in the stator 12.
• an air gap scattering field 3 forms in the air gap 17 with tangential to the rotor surface and radial field components, which is measured with one or more so-called air gap sensors 18.
• the air gap sensor 18 was used exclusively for detecting rotor windings, which is manifested by a clear change in the amplitude of the measured stray field 3 at a specific angular position of the rotor arrangement.
• the solution according to the method provides for a further analysis of the output signal of the air gap sensor 18.
• the output signal of the air gap sensor 18 is therefore a periodic alternating signal with pronounced harmonics of the nominal rotor rotational frequency.
• the output signal has a harmonic in the range of the number of slots N, ie, a spectral component at N times the rated rotor rotational frequency.
• Torsional movements or rotational fluctuations of the rotor 1 1, and thus of the shaft 10 are expressed in fluctuations of the phase angle of this signal or in fluctuations of the phase angle of the individual harmonics of this signal, a phenomenon that equals a phase or frequency modulation.
• the output signals of the air gap sensor 18 are therefore demodulated in order to separate the phase change, which is to be expected from the nominal rotational movement of the rotor assembly, from the phase fluctuations due to torsional movements.
• the output signal is preferably examined simultaneously in different frequency ranges, in particular at the harmonics of the nominal rotor rotational frequency.
• the harmonics of the time function s k (t) of the stray field can be formulated by the following relationship:

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• 2009
  • 2009-04-01 CN CN200980119129.1A patent/CN102047084B/zh not_active Expired - Fee Related
  • 2009-04-01 EP EP09753716A patent/EP2265911A2/de not_active Withdrawn
  • 2009-04-01 WO PCT/EP2009/053892 patent/WO2009144061A2/de active Application Filing
• 2010
  • 2010-10-12 US US12/902,346 patent/US8378645B2/en active Active

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