JP2003274691A - Method and device for detecting abnormality of rotor in ac motor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To make influence of noise to be minimum and to easily detect abnormality of a rotor in an AC motor even in an operation state. <P>SOLUTION: Subtraction is performed in current frequencies (similar phase waveforms) for one continuous cycle in a current flowing in the AC motor 1, which is detected by a current detector 5. Thus, a pulsation component appeared in a case of abnormality in the rotor is extracted and presence or absence of abnormality of the rotor is detected. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rotor abnormality detection method for an AC motor and a rotor capable of detecting abnormality of the rotor of the AC motor even in an environment where there is a lot of electrical noise and during operation. The present invention relates to an abnormality detection device.

[0002]

2. Description of the Related Art As a conventional device for detecting an abnormality of a rotor of an AC motor during operation, there is a bar burnout diagnosis device. In this device, FFT analysis is performed on the current flowing in the AC motor, and internal abnormalities such as the rotor are detected from the frequency components that appear as sidebands of the power supply frequency component (FFT analysis: How to proceed with electrical equipment diagnostics (Publisher: Nippon Plant (Maintenance Association) Issued the first edition of the first printing December 15, 1993
Sun, see).

Here, the above-mentioned diagnosis device is not usually always installed in the electric motor, but is appropriately attached and diagnosed 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 the rotor abnormality can be detected early,
Normally, you only need to repair the rotor.

[0004]

However, when trying to detect the abnormality of the rotor as described above, the current probe (current detector) for detecting the current and the rotation detector for detecting the number of rotations of the rotor are required. Will be needed. In particular, it is difficult to attach the rotation detector unless the electric motor is stopped once. Even when the electric motor is in a normal state, the electric current that flows in the electric motor is superposed with electrical noise that occurs when the power source is controlled by an inverter, etc. The difference from the current spectrum when the bar of the rotor is cut is slight, and skill is required to determine whether the rotor is abnormal. Figure 6 shows the frequency spectrum of the current under normal conditions.
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 the spectra is slight. In the figure, P (f-
2sf) and P (f + 2sf) are sideband components involved in abnormal pulsation. In addition, the amplitude difference in the figure is the sideband wave and P
It represents the amplitude difference between (s).

Further, as a drawback of the FFT analysis in the above detection method, there is a discontinuity of the measured value (measurement does not always start from 0 point (amplitude = 0)), and therefore an error is caused by using the window function. However, if the current signal itself is distorted due to power source harmonics, etc.,
The error becomes complicated, and many noise components similar to sidebands are often superimposed. From this point as well,
Rotor abnormality detection becomes cumbersome.

The present invention has been made by paying attention to the above problems, and easily detects an abnormality of the rotor of an AC motor even in an operating state by minimizing the influence of noise. An object of the present invention is to provide a rotor abnormality detection method and a rotor abnormality detection device for an AC electric motor capable of performing the same.

[0007]

In order to solve the above-mentioned problems, the invention described in claim 1 of the present invention subtracts two waveforms having the same phase in the current flowing through the AC motor. The present invention provides a rotor abnormality detection method for an AC motor, which is characterized by detecting the presence or absence of abnormality of the rotor based on the components extracted in this way. Next, in the invention described in claim 2, in contrast to the configuration described in claim 1, the two waveforms are waveform portions that are in the same phase and exist in a waveform for two consecutive cycles. It is characterized by being.

Next, in the invention described in claim 3, the current detecting means for detecting the current flowing in the AC motor and the waveforms of the adjacent same phase portions among the current waveforms detected by the current detecting means are subtracted from each other. By providing an extracting means for extracting a pulsating component, and an abnormality determining means for detecting an abnormality of the rotor based on the component extracted by the extracting means, a rotor abnormality detecting device for an AC electric motor is provided. is there. According to the present invention, by subtracting waveforms having the same phase from each other in the current flowing through the AC motor, the power source frequency component, the harmonic component synchronized with the power source frequency, and the power source frequency such as the thyristor current surge are synchronized. The noise component is canceled (erased) or largely canceled (erased), and the pulsating component associated with the rotor abnormality is extracted.

When the pulsation component is continuously acquired, the pulsation component at the time of abnormality is detected as a waveform having a long cycle (for example, 3 to 4 Hz) at the time of abnormality, and it is possible for the unskilled person to reliably detect the abnormality. Further, since the noise components such as the thyristor current surge that are synchronized with the power supply frequency are periodically mixed in substantially the same phase position and with the same waveform, as described above, the waveforms of the same phase are subtracted from each other. This can be offset. In particular, this effect can be canceled more reliably by performing the effect between adjacent identical waveforms. The more the two in-phase waveform positions are apart from each other, the greater the possibility that the noise position is displaced.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a configuration diagram showing an anomaly detection device adopting the anomaly detection method of the present invention.
In FIG. 1, reference numeral 1 indicates an electric motor, reference numeral 2 indicates a three-phase electric wire for supplying electric power to the electric motor 1, reference numeral 3 indicates a power source, and reference numeral 4 indicates an ammeter. The above-mentioned abnormality detection device includes a current detector 5, an A / D converter 6, a DSP 7 (Digital 1).
Signal1 Processor), a D / A converter 8, and an abnormality determination unit 9.

The current detector 5 detects the 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 current transformer for instruments, and by clipping the wiring of the current measuring circuit of the electric motor 1, the electric current detector 5 can be easily installed even while the electric motor 1 is in operation. 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.

Here, as shown in FIG. 2, when the power supply frequency is 60 Hz, the sampling frequency is 15480H.
When set to z, one cycle's worth of digital data becomes 258, so if each of the registers 11, 12, and 13 described later is set to a register having 258 storages, waveforms are continuously generated at each cycle. Data can be stored. In DSP7, in synchronization with the cycle of the power supply frequency,
A digital signal for one cycle from the input signal is stored in the first register 11, and subsequently, a signal delayed by one cycle of the power supply frequency is stored in the second register 12. Next, by subtracting the second register 12 from the first register 11, the signal synchronized with the power supply frequency is erased, and the subtraction result is written in the third register 13. The content of this third register 13 is D
After being converted into an analog signal by the / A converter 8, it is output to the abnormality determination unit 9. This DSP 7 constitutes the extraction means.

Here, the second register 1 after the above subtraction processing
The contents of 2 are shifted to the first register 11, the digital data for one subsequent period is stored in the second register 12, and the subtraction process is performed. This process is repeatedly performed by the DSP 7. The abnormality determination unit 9 determines whether or not there is an abnormality in the rotor based on the analog signals continuously input. When the motor 1 is not abnormal, the signal input to the determination unit is a zero signal, while when the rotor is abnormal, there is a pulsating component. Therefore,
Even an unskilled person can make a determination, and automatic determination is easy.

That is, when the cycle of the power supply frequency is 60 Hz, the pulsating component of the analog signal continuously input to the above-mentioned judging section is as shown in FIG. 3, for example, when the rotor is abnormal. While it is detected as a long cycle wave of about 4 to 5 Hz, if there is no abnormality in the rotor, the above waveform does not exist. The determination is easy.
Further, when the FFT analysis device is adopted as the abnormality determination unit 9, frequency analysis of the pulsating component is performed. When this FFT analysis is performed and there is an abnormality in the rotor, for example, as shown in FIG.
As shown in, a clear peak value appears around 2 to 6 Hz, but no clear peak value appears when there is no abnormality in the rotor. Therefore, the abnormality of the rotor is surely detected.

The pulsating current that appears when the rotor is abnormal is a pulsating current having a peak at (2 · s · f). The s indicates the slip value, and the f indicates the frequency. Therefore, a more accurate determination can be made by identifying the frequency of the peak value corresponding to the slip value s and determining whether or not there is a spectrum having a peak of a predetermined magnitude at the identified frequency.

For example, in a motor 1 having a frequency of 60 Hz and two poles, a synchronous speed is 3600 rpm and an actual speed is 3500.
If rpm, then the slip value s = ((3600-350
0) / 3600) ≈3%. Therefore, 2 · s ·
f = 2 · (3/100) · 60 = 3.6Hz,
It is possible to confirm whether or not the pulsation at the time of the above abnormality occurs 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 of zero amplitude, that is, the measured values are discontinuous, it is not necessary to use the window function as in the conventional case.

Further, in the case where the judging section automatically judges, when an abnormality is detected, an abnormality signal is output to the notifying means 10 such as a speaker. Here, in the above embodiment, the adjacent 1
Every cycle, that is, W1, W2, and W in FIG.
Although the waveforms to be subtracted are set as 2 and W3, W3 and W4, ..., The waveforms for subtracting the same phase portion in two adjacent cycles such as Y1 and Y2 may be used. In addition, a combination of subtraction such as W1 and W2 and W3 and W4 may be set. Further, although the accuracy is slightly lowered, the subtraction processing may be performed between the same waveforms at positions that are not adjacent to each other like W1 and W3.

[0018]

As described above, when the present invention is adopted, the pulsating component generated when an abnormality such as a bar break occurs in the rotor of the AC motor eliminates power source noise including harmonic noise. Therefore, the abnormality can be detected with high accuracy.

[Brief description of drawings]

FIG. 1 is a diagram illustrating a device configuration according to an embodiment based on the present invention.

FIG. 2 is a diagram illustrating a process of the abnormality detection device according to the embodiment based on the present invention.

FIG. 3 is a diagram showing an example of waveforms of continuously extracted pulsation components according to an embodiment of the present invention.

FIG. 4 is a diagram showing an example of an FFT-analyzed frequency spectrum according to an embodiment of the present invention.

FIG. 5 is a diagram showing an example of a current waveform according to an 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 bar of a rotor is cut.

[Explanation of symbols]

1 electric motor 2 electric wires 3 power supplies 5 Current detector (current detection means) 6 A / D converter 7 DSP (extractor) 8 D / A converter 9 Abnormality determination unit (abnormality determination means) 11 First register 12 Second register 13 Third register

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Claims (3)

[Claims] 1. An AC motor characterized in that the presence or absence of abnormality of a rotor is detected based on a component extracted by subtracting two waveforms having the same phase from each other in a current flowing through the AC motor. Rotor abnormality detection method. 2. The rotor for an AC motor according to claim 1, wherein the two waveforms are waveform portions that are present in a waveform for two consecutive cycles and have the same phase with each other. Anomaly detection method. 3. A current detecting means for detecting a current flowing through an AC motor, and a current waveform detected by the current detecting means,
An alternating current motor comprising: an extracting unit that extracts a pulsating component by subtracting waveforms of adjacent same phase portions; and an abnormality determining unit that detects an abnormality of the rotor based on the component extracted by the extracting unit. Rotor abnormality detection device.