JP4062939B2 - Rotor abnormality detection method and rotor abnormality detection apparatus for AC motor - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a rotor abnormality detection method and a rotor abnormality detection device for an AC motor that can detect an abnormality in a rotor of an AC motor even in an environment with a lot of electrical noise and during operation. .
[0002]
[Prior art]
As a conventional device for detecting an abnormality of a rotor of an AC motor during operation, there is a bar breakage diagnosis device. This device performs FFT analysis on the current flowing through the AC motor and detects internal abnormalities such as rotors from the frequency components that appear as sidebands of the power supply frequency component (FFT analysis: How to proceed with electrical equipment diagnosis (Publisher: Japan Plant) (Maintenance Association) issued the first edition of the first edition, December 15, 1993).
[0003]
Here, the diagnosis apparatus as described above is generally not always installed in the electric motor, but is appropriately attached when making a diagnosis.
Further, if the operation of the electric motor is continued without noticing the abnormality of the rotor, the electric motor itself may be fatally damaged, and the electric motor itself may be required to be replaced. On the other hand, if abnormality of the rotor can be detected at an early stage, it is usually only necessary to repair the rotor.
[0004]
[Problems to be solved by the invention]
However, in order to detect an abnormality of the rotor as described above, a current probe (current detector) for detecting current and a rotation detector for detecting the rotation speed of the rotor are required. In particular, it is difficult to mount the rotation detector unless the motor is stopped once.
In addition, even when the motor is in a normal state, the electric current generated when the power is controlled by an inverter or the like is superimposed on the current flowing through the motor. The difference from the current spectrum when the rotor bar is cut is slight, and skill is required to determine whether the rotor is abnormal. FIG. 6 shows the frequency spectrum of the current when normal, and FIG. 7 shows the frequency spectrum of the current when the rotor bar is cut. As can be seen from FIGS. 6 and 7, the difference in spectrum is slight. In the figure, P (f−2sf) and P (f + 2sf) are sideband components involved in abnormal pulsation. The amplitude difference in the figure represents the amplitude difference between the sideband and P (s).
[0005]
In addition, as a disadvantage of the FFT analysis in the above detection method, there is a discontinuity of the measurement value (measurement does not necessarily start from 0 point (amplitude = 0)), so that the error correction is performed using a window function. However, when the current signal itself is distorted by power supply harmonics or the like, the error becomes complicated, and many noise components similar to sidebands are often superimposed. Also from this point, the abnormality detection of the rotor becomes troublesome.
[0006]
The present invention has been made paying attention to the above-mentioned problems, and it is possible to easily detect an abnormality in the rotor of an AC motor even if it is in an operating state with a minimum effect of noise. An object of the present invention is to provide a rotor abnormality detection method and a rotor abnormality detection device for a simple AC motor.
[0007]
[Means for Solving the Problems]
In order to solve the above problems, the invention described in claim 1 of the present invention is based on a component extracted by subtracting two waveforms having the same phase in the current flowing in the AC motor. An object of the present invention is to provide a rotor abnormality detection method for an AC motor, characterized by detecting the presence or absence of a child abnormality.
Next, the invention described in claim 2 is the same as the structure described in claim 1, but the two waveforms are waveform portions that exist in the waveform for two consecutive cycles and have the same phase. It is characterized by being.
[0008]
Next, the invention described in claim 3 pulsates by subtracting adjacent waveforms of the same phase portion from the current detection means that detects the current flowing through the AC motor and the current waveform detected by the current detection means. The present invention provides an AC motor rotor abnormality detection device comprising: an extraction means for extracting a component; and an abnormality determination means for detecting an abnormality of the rotor based on the component extracted by the extraction means.
According to the present invention, by subtracting between waveforms of the same phase among the currents flowing in the AC motor, the power supply frequency component, the harmonic component synchronized with the power supply frequency, and the power supply frequency such as a thyristor current surge are synchronized. The noise component is canceled (erased) or greatly canceled (erased), and the pulsation component accompanying the rotor abnormality is extracted.
[0009]
When the pulsation component is acquired continuously, the pulsation component at the time of abnormality is detected as a long-period waveform (for example, 3 to 4 Hz) at the time of abnormality, and it is possible to reliably detect the abnormality even if it is not an expert.
In addition, since noise components synchronized with the power supply frequency such as the thyristor current surge are usually periodically mixed at substantially the same phase position and in the same waveform, they are subtracted between waveforms having the same phase as described above. Can be offset. In particular, this effect can be canceled more reliably by performing the effect between adjacent identical waveforms. The farther the two identical phase waveform positions are, the greater the possibility that the noise position will shift.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
Next, embodiments according to the present invention will be described with reference to the drawings.
FIG. 1 is a block diagram showing an abnormality detection apparatus employing the abnormality detection method of the present invention.
In FIG. 1, reference numeral 1 denotes an electric motor, reference numeral 2 denotes a three-phase electric wire that supplies electric power to the electric motor 1, reference numeral 3 denotes a power source, and reference numeral 4 denotes an ammeter.
The abnormality detection device includes a current detector 5, an A / D converter 6, a DSP 7 (Digital 1 Signal 1 Processor), a D / A converter 8, and an abnormality determination unit 9.
[0011]
The current detector 5 detects a current flowing through the electric motor 1 and outputs the detected current signal to the A / D converter 6. The current detector 5 is composed of, for example, a split-type instrument current transformer, and can be easily installed even when the motor 1 is in operation by clipping the wiring of the current measuring circuit of the motor 1. It is possible to determine the abnormality of the rotor by detecting the current.
The A / D converter 6 converts the input signal into a digital signal and outputs it to the DSP 7.
[0012]
Here, as shown in FIG. 2, when the power supply frequency is 60 Hz and the sampling frequency is set to 15480 Hz, one cycle corresponds to 258 digital data. If a register having 258 storage units is set, waveform data can be stored continuously every cycle.
In the DSP 7, in synchronization with the cycle of the power supply frequency, the digital signal for one cycle from the input signal is stored in the first register 11, and subsequently, the signal delayed by one cycle of the power supply frequency is stored in the second register 12. To do. Next, by subtracting the second register 12 from the first register 11, the signal synchronized with the power supply frequency is deleted, and the subtraction result is written in the third register 13. The contents of the third register 13 are output to the abnormality determination unit 9 after being converted into an analog signal by the D / A converter 8. This DSP 7 constitutes extraction means.
[0013]
Here, the contents of the second register 12 after the subtraction process are shifted to the first register 11, and the digital data for one subsequent period is stored in the second register 12, and the subtraction process is performed. This process is repeated in the DSP 7.
The abnormality determination unit 9 determines the presence / absence of an abnormality of the rotor based on continuously input analog signals. When no abnormality has occurred in the electric motor 1, the signal input to the determination unit is a zero signal. On the other hand, when there is an abnormality in the rotor, there is a pulsating component. Therefore, determination can be made even by a non-expert, and automatic determination is easy.
[0014]
That is, the analog signal continuously input to the determination unit has a pulsation component of 4 to 4 as shown in FIG. While detected as a long-period wave of about 5 Hz, the above waveform does not exist when there is no abnormality in the rotor. Therefore, even if it is manually confirmed by an oscilloscope etc. It is.
Further, when an FFT analyzer is adopted as the abnormality determination unit 9, a frequency analysis of pulsation components is performed. When this FFT analysis is performed, when there is an abnormality in the rotor, for example, as shown in FIG. 4, a clear peak value appears around 2 to 6 Hz, but when there is no abnormality in the rotor, A clear peak value does not appear. Therefore, the rotor abnormality is reliably detected.
[0015]
Here, the pulsating current that appears when the rotor is abnormal is a pulsating current having a peak at (2 · s · f). The s indicates a slip value, and f indicates a frequency.
Therefore, the frequency of the peak value corresponding to the slip value s is specified, and a more accurate determination can be made based on whether or not there is a spectrum having a peak of a predetermined size at the specified frequency.
[0016]
For example, if the frequency is 60 Hz and the electric motor 1 has two poles, the synchronous speed is 3600 rpm, and the actual speed is 3500 rpm,
The slip value s = ((3600-3500) / 3600) ≈3%. Therefore, 2 · s · f = 2 · (3/100) · 60 = 3.6 Hz, and it is possible to confirm whether the pulsation is abnormal or not by the pulsation having a peak at 3.6 Hz.
In the FFT analysis, even if the start position of each identical waveform portion is not the zero point with zero amplitude, that is, even if the measurement value is discontinuous, it is not necessary to use a window function as in the prior art.
[0017]
When the determination unit automatically determines, when an abnormality is detected, an abnormality signal is output to the notification means 10 such as a speaker.
Here, in the above embodiment, the waveform to be subtracted is set for each adjacent cycle, that is, W1 and W2, W2 and W3, W3 and W4,... In FIG. It is good also as a waveform which subtracts the same phase part in two adjacent cycles like Y1 and Y2. Further, a combination of subtraction such as W1 and W2, W3 and W4 may be set. In addition, although the accuracy is slightly reduced, the subtraction process may be performed between the same waveforms at positions that are not adjacent to each other, such as W1 and W3.
[0018]
【The invention's effect】
As described above, when the present invention is adopted, it is possible to detect a pulsation component generated when an abnormality such as bar breakage occurs in the rotor of an AC motor by eliminating power supply noise including harmonic noise. Therefore, the abnormality can be detected with high accuracy.
[Brief description of the drawings]
FIG. 1 is a diagram illustrating a device configuration according to an embodiment of the present invention.
FIG. 2 is a diagram for explaining processing of the abnormality detection device according to the embodiment of the present invention.
FIG. 3 is a diagram showing an example of a waveform of continuously extracted pulsation components according to an embodiment of the present invention.
FIG. 4 is a diagram showing an example of a frequency spectrum subjected to FFT analysis according to an embodiment of the present invention.
FIG. 5 is a diagram showing an example of a current waveform according to the embodiment of the present invention.
FIG. 6 is a diagram showing an example of a frequency spectrum when the electric motor is normal.
FIG. 7 is a diagram showing an example of a spectrum when a rotor bar is cut.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Electric motor 2 Electric wire 3 Power supply 5 Current detector (current detection means)
6 A / D converter 7 DSP (extraction means)
8 D / A converter 9 Abnormality determination unit (abnormality determination means)
11 First register 12 Second register 13 Third register

Claims (3)

A rotor abnormality detection method for an AC motor characterized by detecting the presence or absence of a rotor abnormality based on a component extracted by subtracting two waveforms having the same phase in the current flowing through the AC motor. . 2. The AC motor rotor abnormality detection method according to claim 1, wherein the two waveforms are waveform portions having the same phase as each other and existing in waveforms for two consecutive cycles. Current detection means for detecting the current flowing in the AC motor, extraction means for extracting the pulsation component by subtracting the waveforms of adjacent identical phase portions from the current waveforms detected by the current detection means, and extraction means for extraction And an abnormality determining means for detecting abnormality of the rotor on the basis of the component thus obtained.

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