JPS61167884A - Diagnostic device for fracture of rotor conductor of induction motor - Google Patents

Abstract

PURPOSE:To diagnose the fracture state of a rotor conductor by deriving the power ratio of the power source frequency component and beat frequency component in a current which flows through a stator winding. CONSTITUTION:The primary current of the stator winding of an induction motor 25 flows through a current transformer 1 and a current-voltage converting circuit 2 to input a voltage proportional to the primary current to a frequency analyzing circuit 4, which detect frequency characteristics, thereby reading frequency components in the input waveform from the extremal value of the characteristic curve. Further, a detection coil is arranged in the gap between a stator and a rotor, an induced voltage due to leak magnetic flux of a revolving magnetic field produced with the secondary current of the rotor conductor is detected by a leak magnetic flux detecting circuit 7, and an LPF8 remove the power source frequency component in the induced voltage to extract only a slide frequency component. Then, a beat frequency derived from a frequency detecting circuit 9 and the frequency component contained in the current of the stator winding which is calculated by the circuit 4 are passed through a frequency discriminating circuit 6 and a power ratio arithmetic circuit 10 calculates the power ratio of the power source frequency component and the frequency component obtained by the circuit 6 to diagnose the fracture state of the rotor conductor.

Description

[Detailed description of the invention] [Technical field to which the invention pertains]

The present invention relates to a device that detects a beat phenomenon contained in a current flowing through a stator winding of an induction motor and diagnoses the presence or absence of a break in a rotor conductor of the induction motor.

[Prior art and its problems]

The rotor of an induction motor consists of an iron core and a conductor through which secondary current flows (
It consists of a short-circuit ring (hereinafter abbreviated as bar) and a short-circuit ring. The bars are located in grooves on the outer circumference of the rotor, and several dozen bars are arranged at equal intervals on the circumference. Under normal operating conditions of the motor, if the frequency of the rotating magnetic field generated from the stator @ wire is f., the frequency of the rotating magnetic field generated in the rotor winding with one rotor as a reference is af. (Here, 3 is Therefore, during normal operation of the motor, the rotational frequency of the rotating magnetic field generated from the rotor wires with respect to the stator is the same speed as (1-s) fe + sfo -f@ wave number, and the stator The current flowing through the @ line does not pulsate; this is the same even when the periphery S changes during operation. By the way, when a part of the bar breaks due to heating due to centrifugal force or starting current during operation, an imbalance occurs in the secondary current of the rotor, and the frequency corresponds to af. A negative sequence current is generated whose rotation direction is opposite to that of the rotor. Therefore, a current with a frequency fe (1-2 s) is generated in the stator winding, which is 2 sf smaller than the fundamental frequency f. Therefore, in the stator winding of the electric motor,
Since the current at the fundamental frequency f and the current at the frequency f* (1-2 g) induced from the rotor flow in a heavy manner, a beat phenomenon occurs in the current waveform, and the amplitude of this current waveform is fa-fo. (1-2a) It fluctuates at a period equivalent to 2sf. When the number of broken bars increases, the unbalanced current in the rotor's secondary current increases, making it impossible to start the motor. Stator and Rotation The magnetic attraction force that acts between the rotor and the rotor is distributed asymmetrically around the rotor due to the non-uniform distribution of the secondary current caused by the bar breakage.This asymmetrical magnetic attraction force and the rotating magnetic field due to the opposite phase secondary current , the rotor has a rotational frequency f of the rotor.
In addition to , an excitation force having a frequency of f, ±2 sfo acts on the motor, generating vibrations in the motor. This vibration vibrates at a frequency of fl, and the amplitude produces a beat phenomenon at a frequency of 23f6. However, such a vibration phenomenon also occurs due to eccentric rotation of the rotor (due to shaft bending), so even if the vibration or noise of the motor causes a humming phenomenon, it is dangerous to diagnose a bar breakage based on that alone. Conventionally, when a beat phenomenon occurs in vibration, as shown in Figure 3, the current waveform (a) of the stator winding and the vibration waveform (false) are recorded on an oscilloscope, and the beat period of both waveforms is read. The beat periods of both waveforms match, and the period is 1/2
If it was sfo seconds, it was diagnosed as a broken rotor bar. However, when the number of broken bars is very small, the amount of amplitude fluctuation in the current waveform shown in FIG. 3(a) is small, so diagnosis using this method requires skill. For this reason,
For example, as shown in Japanese Patent Application Laid-Open No. 56-153959,
Only the beat frequency or pulsation frequency contained in the current flowing through the stator winding is extracted using a filter, and this frequency is counted using a counter and obtained by a tachometer connected to the rotor of the motor. Rotation speed N
The circuit is configured to obtain the beat frequency that should be included in the stator winding current when the bar is broken from the synchronous speed No. obtained from the power supply frequency f using the following formula; A method is known in which the presence or absence of a bar breakage is diagnosed by comparing the output of a frequency detector. However, to measure rotational speed, pulses obtained using, for example, a magnetic pulse detector or a photoelectronic pulse detector are input into a rotational speed analysis circuit.
It is necessary to use a rotation frequency selection circuit to select the center rotation frequency from among the rotation frequency components analyzed by this circuit, and the measurement is not necessarily simple. In addition, in recent years, a diagnosis method using FFT analyzer (Foury frequency analysis) has been used. Figure 4 shows the analysis results of the stator winding current using this FFT analyzer, and Figure 5 shows the vibration analysis results. Although high diagnostic accuracy can be obtained with this method, in order to obtain this diagnostic accuracy, it is necessary to use the FFT analyzer in such a way that a frequency resolution of 0-01 = 0.05H2 can be obtained, and it requires specialized knowledge. Because this method requires several technicians for each analysis, it lacks the speed and ease of diagnosis.

[Object of the Invention] The present invention eliminates the above-mentioned drawbacks, and is determined independently of the current flowing through the stator winding of an induction motor that has caused rotor bar breakage, and is included in the current flowing through the stator winding. The objective is to more easily measure the beat frequency to be compared with the detected beat frequency, thereby making diagnosis easier. [Summary of the Invention] This invention detects the beat phenomenon included in the current flowing in the stator winding of an induction motor and analyzes the frequency components included in the current waveform flowing in the stator winding of the induction motor. a beat frequency detection circuit that measures the leakage magnetic flux of the rotor of the induction motor and detects the beat frequency to be included in the stator winding; a beat frequency discrimination circuit that determines whether a beat frequency component exists in the frequency components analyzed by the frequency detection circuit; and a power ratio between the power supply frequency component and the beat frequency component in the current flowing through the stator winding. It is equipped with a power ratio calculation circuit and a display circuit that digitally displays the power supply frequency, the beat frequency, and the power ratio, respectively. This method aims to achieve the above-mentioned objective by simplifying the measurement compared to the method of determining the frequency.

[Embodiments of the invention]

FIG. 1 shows an embodiment of the circuit configuration of a diagnostic device according to the present invention, in which a primary current flowing into the stator winding of an induction motor 25 is detected using a current transformer 1. The resulting current is input to the current-voltage conversion circuit 2 and converted into a voltage proportional to the current. This voltage proportional to the primary current is amplified by the amplifier circuit 3 and input to the frequency analysis circuit 4. Reference numeral 5 denotes a circuit for setting the center frequency of the frequency range analyzed by the frequency analysis circuit 4, which is set to either 50Hz or 60Hz depending on the power frequency of the diagnostic location, and this signal is set to 0 frequency to the frequency analysis circuit 4. The analysis circuit 4 is based on the same principle as the above-mentioned FFT analyzer (it is a frequency analysis circuit,
The frequency components included in the voltage waveform input from the amplifier circuit 3 are analyzed with a resolution of, for example, 0.05 Hz. That is, while reading the voltage or power that develops the frequency component at each pitch of 0.05Hz, the frequency characteristic of the voltage or power as shown in Figure 4 is detected, and from the extreme value of this characteristic curve, the input waveform is determined. Read the frequency components contained in. On the other hand, in order to find the beat frequency that should be compared with the beat frequency included in the current flowing through the stator winding of the induction motor, independent of the current flowing through the stator winding, the , 100 coils 15 on a small bobbin 16
A detection coil 17 formed by winding approximately one turn is placed close to the rotor in the gap between the stator and rotor, and its axial direction is aligned with the circumferential direction of the rotor so that it is connected to the stator side. When fixed to , a voltage is induced in this detection coil by the leakage magnetic flux of the rotating magnetic field generated from the secondary current flowing in the five-rotor conductor. The leakage flux detection circuit 7 is a circuit that detects the voltage induced in this way, but since this induced voltage includes a power supply frequency component, this voltage is passed through the low-pass filter 8. By removing the power supply frequency component and extracting only the slip frequency component, and inputting this slip frequency component to the beat frequency detection circuit 9, the beat frequency that should be included in the current flowing to the stator winding can be determined from the input voltage. Desired. This determined beat frequency was obtained in the frequency analysis circuit 4. The frequency components included in the current flowing through the stator windings are manually input to the beat frequency discrimination circuit 6.
? It is determined whether there is a frequency component that is different from the beat frequency obtained from IhD m + notb t-et, + W oil m. When this matching frequency component exists, the power ratio calculation circuit 10 measures the respective powers of the power supply frequency component in the stator winding current and this failed frequency component, and calculates the ratio.
This ratio is digitally displayed in real time on the power ratio display circuit 13, and the power supply frequency and beat frequency are digitally displayed on the display circuits 11 and 12, respectively. Power ratio [
The relationship between the number of broken rotor conductors (normally expressed in dB (decibels)) and the number of broken rotor conductors has been clarified in advance through experiments as shown below, and the diagnostician can determine the state of rotor conductor breakage based only on the displayed power ratio. can be diagnosed. =1.5dB or less---Crack level, 3.1lk
dB or less --- Cracks and 1 conductor break or less, 5.0 dB or less --- 3 conductor breaks or less. Therefore, based on this diagnosis result, even if a broken bar on the rotor is detected, the motor should not be stopped in vain, and the timing of disassembly and repair of the motor can be planned according to the degree of broken bar, and the motor should be restarted. This can contribute to efficient operation of the equipment used.

【Effect of the invention】

As described above, according to the present invention, there is no need for oscillographic measurement of stator winding current or motor vibration, which requires skill in reading waveforms; Instead of measuring the current and rotational speed, which requires a complicated measurement process, the voltage obtained from the leakage flux of one rotor is used to determine the beat frequency that should be included in this stator current regardless of this stator current. By simply inputting the following, the data necessary for diagnosing the rotor conductor breakage status is immediately displayed.In addition to immediately diagnosing the presence or absence of a rotor conductor breakage, it is also possible to determine the number of broken rotor conductors. It can be easily estimated and accidents can be prevented. In addition, unnecessary measures such as immediately stopping the operation of the motor when the number of broken stator conductors is extremely small are eliminated, and the timing of disassembly and repair of the motor can be planned based on the estimated number of broken conductors. This has the effect of contributing to efficient operation of equipment using electric motors.

[Brief explanation of drawings]

Fig. 1 is a block circuit diagram showing the circuit configuration of a rotor conductor fracture diagnosis device based on the present invention, Fig. 2 is a sketch of a detection coil for detecting leakage magnetic flux of the rotor, and Fig. 3 is a diagram showing a rotor conductor fracture. Figure 4 shows the frequency components included in the stator current when the rotor conductor is broken. The output waveform from this analyzer when analyzed by the FFT analyzer, and FIG. 5 shows the output waveform from this analyzer when the frequency component of the vibration waveform of the electric motor is analyzed by the same FFT analyzer. 4: Frequency analysis circuit, 6: Beating frequency discrimination circuit, 7:
Leakage flux detection circuit, 9: Beating frequency detection circuit, 10:
Power ratio calculation circuit, 11: Power supply frequency loss Figure 1
Figure 2 Figure 3 Figure 4

Claims (1)

[Claims] 1) A device for diagnosing the presence or absence of a break in the rotor conductor of the induction motor by detecting a beat phenomenon included in the current flowing in the stator winding of the induction motor, the current flowing in the stator winding of the induction motor A frequency analysis circuit that analyzes frequency components included in the current waveform; a beat frequency detection circuit that measures the leakage magnetic flux of the rotor of the induction motor to detect the beat frequency that should be included in the stator winding; a beat frequency discrimination circuit that determines whether a frequency matching the beat frequency exists in the frequency components analyzed by the frequency detection circuit; and a beat frequency component and the beat frequency in the current flowing through the stator winding. A rupture diagnostic device for an induction motor rotor conductor, comprising: a power ratio calculation circuit that calculates a power ratio with respect to a component; and a display circuit that digitally displays each of the power supply frequency, beat frequency, and power ratio.