JPS6021800Y2 - Rotor bar breakage detection device for squirrel cage induction machine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a device for detecting breakage of a rotor bar in a squirrel cage induction machine.

When a rotating machine, especially a squirrel-cage induction machine, is started and stopped repeatedly over many years, the rotor bar is subject to stresses such as thermal stress due to copper loss, vibration due to electromagnetic force, and centrifugal force.
Eventually, the rotor bar may break.

Broken rotor bars not only cause a reduction in induction motor output, but also the current cut off due to the breakage is borne by other healthy bars, so even healthy bars are subject to excessive stress compared to when they are normal. This may lead to further accidents resulting in breakage.

Also, if operation continues with a broken rotor bar,
There is also the risk of the broken bar turning over and damaging the stator windings.

Therefore, it is important to detect rotor bar breakage before the accident escalates to prevent serious damage to the induction machine.

The present invention was conceived in view of the above-mentioned circumstances, and it is an object of the present invention to provide a detection device that can reliably detect breakage of a rotor bar without becoming complicated or expensive.

According to the research conducted by the inventors of the present invention, it was discovered that among the magnetomotive force harmonics on the rotor side, a predetermined frequency component induced by slot harmonics on the stator side changes significantly depending on whether or not the rotor bar is broken. This was also confirmed through experiments.

Therefore, the detection device according to the present invention detects a predetermined order of slot harmonics from the gear tooth magnetic flux, which includes many harmonic components (for example, stator and rotor magnetomotive force harmonics, gap harmonics) in addition to power frequency components. The slip frequency component is extracted and the presence or absence of rotor bar breakage is detected by monitoring the level of this frequency component.

Examples of the present invention will be described below.

FIG. 1 shows the overall configuration, and a squirrel cage induction machine 1 is provided with a sensor 2 for detecting magnetic flux at its gear part from leakage magnetic flux.

As shown in FIG. 2, this sensor 2 includes at least one turn of a search coil 6 wound and fixed at the tip of the tooth 5 of the stator core along the wedge 4 of the stator coil 3. This can be realized by detecting the voltage E (=-dφ/dt) induced in the coil 5 with respect to the time change of the gap magnetic flux φ.

Alternatively, the Hall element 7 may be fixed to the tooth 5 side end of the stator core with an adhesive or the like, and the gap magnetic flux change may be detected from the Hall element 7.

In addition, a magnetically sensitive element that detects a change in magnetic flux as a change in resistance value can also be used.

By passing the gear part magnetic flux signal detected by the sensor 2 through a bandpass filter 10, a predetermined order ν of the slot harmonic is obtained.
The slip frequency component Sν·f of is extracted.

This Sν・f is Sν・f=(1-ν(1-5))f
......It is expressed as (1).

Note that f is the power supply frequency, S is the slip with respect to the fundamental wave, and ν
is the harmonic order determined by the number of grooves q for each pole and each phase of the stator.

Therefore, the center frequency of the pass frequency band of the band-pass filter 10 is set to Sν·f, but in practice S is very small, so Sν·f=(1-ν)·f...・(2
).

The output of the bandpass filter 10 is amplified to an appropriate level by an amplifier 11.

This amplifier 11 is not required when the output of the sensor 2 is large or when the bandpass filter 10 is provided with an amplification function.

Further, the amplifier 11 may be installed before the bandpass filter 10.

A differentiating circuit 12 is provided after the amplifier 11.

This differentiating circuit 12 is preferable when the above-mentioned Hall element is used as the sensor 2, and since the detection level of the Hall element changes less depending on the presence or absence of a broken bar than the search coil, the signal passing through the filter 10 is Breakage detection is facilitated by extracting the rate of change.

A comparator 13 detects the level of the signal of the slip frequency component Sv·f obtained through the above-mentioned bandpass filter 10, amplifier 11, and differentiation circuit 12.

The comparison reference level of the comparator 13 is set higher than the Sv.f signal level when the rotor bar is not broken, and lower than the Sv.f signal level when the rotor bar is broken.

The annunciator 14 notifies rotor bar breakage by inverting the output of the comparator 13.

This notification may be made by a buzzer or the like, or by a combination of optical means such as a lamp.

In this way, by extracting the slip frequency component of a predetermined order of slot harmonics of the induction machine from the leakage magnetic flux of the squirrel cage induction machine and determining the magnitude of the level of this frequency component, it is possible to detect whether or not the rotor bar is broken.

As an experimental example, 3.7KW-4P 200V-50H
7 (7) In the induction machine, when q□=3 and Suberi S: 0.043, the slot harmonic order S=±6q1+1=+1 song,
The frequency component Sν·f for the −17th order is calculated from the above-mentioned equation (1) to be S□7·f=86 total (Z, S□9·f=859]7).

Therefore, a band-pass filter 10 having a characteristic passing frequency band of 863H7 or 859H2 was used and the output level of the band-pass filter was measured when the rotor bar was normal and when the rotor bar was broken, and the results shown in the following table were obtained.

As is clear from the above experimental results, when one rotor bar is broken, it is detected as an old level difference compared to the normal state, and when two rotor bars are broken, a level difference of 16 dB occurs, which is a large level difference. Therefore, it can be easily and reliably detected using a comparator with a normal circuit configuration.

Figure 3 shows the induction machine leakage flux in the front stage of the band-pass filter 10 on a spectrum analyzer in the above-mentioned experiment. Figure a shows when the rotor bar is normal, and b shows when one bar is broken. , and C shows the case when two bars are broken.

As shown in FIG. 3, the level of the frequency component at 865H2 changes significantly depending on the presence or absence of bar breakage, and the occurrence of bar breakage can be detected by detecting a level change using a comparator or the like.

Furthermore, since the level changes depending on the number of broken bars, it is possible to detect the number of broken bars by providing a plurality of comparators with appropriate reference levels.

As described above, the detection device according to the present invention extracts the slip frequency component of a predetermined order of the slot harmonic from the leakage magnetic flux of the squirrel cage induction machine, and determines whether or not there is rotor bar breakage based on the level of this slip frequency component. Therefore, it is relatively easy to
It has the effect of being able to reliably detect bar breakage with an inexpensive configuration.

[Brief explanation of the drawing]

Fig. 1 is a configuration diagram showing one embodiment of the present invention, and Fig. 2 is a block diagram showing an embodiment of the present invention.
FIG. 3 is a partial configuration diagram of a stator showing a specific example of the sensor in the figure, and FIG. 3 is a frequency spectrum of the sensor output showing experimental results based on the present invention. DESCRIPTION OF SYMBOLS 1... Squirrel cage induction machine, 2... Sensor, 3... Stator coil, 4... Wedge, 5... Teeth, 6... Wedge coil, 7... Hall element, 10...・Band pass filter, 11 ・Amplifier, 12... Differential circuit, 1
3... Comparator, 14... Alarm.

Claims (1)

[Scope of utility model registration request] a sensor for detecting leakage magnetic flux of the squirrel-cage induction machine; a bandpass filter for extracting a predetermined order slip frequency component of slot harmonics of the induction machine from the detection output of the sensor;
A rotor bar breakage detection device comprising: a comparator that determines whether the rotor bar is broken based on the output level of the filter; and an alarm that notifies the rotor bar breakage based on the determination output of the comparator. .