JPH0422826A - Diagnostic method for looseness of ac motor stator coil - Google Patents

Abstract

PURPOSE:To quantify coil looseness by measuring the vibration of a stator by abutting a vibration meter with the outside of the stator being operated. CONSTITUTION:The vibration of an AC motor stator 6 is measured by abutting the vibration meter 7 with the outside of the stator. At this time, it is desirable to measure the vibration when the idle operation of an AC motor is performed i.e. no load is applied to keep a measuring condition constant. Thence, the measured data of vibration is analyzed by a frequency analyzer 8. At this time, a measuring mode is set at 'displacement'. Furthermore, a component of power source frequency and that doubling the power source frequency are taken out from frequency components sent from the frequency analyzer 8 by a BPF 9. Thence, the degree of coil looseness can be quantified at a coil looseness arithmetic circuit 10.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for diagnosing stator coil slack in an AC motor that does not rely on various conventional hammering methods.

[Conventional method]

Generally, a stator coil 1 of an AC motor is inserted into a core slot 2 of a stator, as shown for example in FIG. 2 as a partial view of the stator, and this coil 1 is fixed in the core slot. For this purpose, a wedge 4 having a trapezoidal cross section made of bamboo, hakelite, etc. is installed in a dovetail groove 3 formed at the top of the core slot. 5 indicates the iron core of the stator.

However, the oil content of the insulator 1b covering the surface of the coil conductor 1a of the stator coil 1 decreases over time, and this phenomenon (referred to as coil withering) causes the coil 1 to shrink. The coil 1 is located between the lower surface of the wedge 4 engaged in the dovetail groove 3 and the coil 1 or within the core slot 2.
Since a gap is created between the coil 1 and the coil 1, the pressing force of the wedge 4 against the coil 1 becomes smaller.

As a result, the insulation of the coil 1 was worn out due to the vibrations generated by the electromagnetic force caused by the alternating magnetic flux, and in the worst case, a grounding accident occurred, and the operation had to be suspended for several days to repair the accident system. There was a problem in that it created a situation where it was necessary to do so.

Therefore, in order to solve this problem, (1) J
IPMS, 57/11. The 7th ``Equipment Diagnosis Technology Basic Course'' proposes the diagnosis method J using the impulse hammering method, (2) the hammering sound check method by experts, etc.

(Problems to be Solved by the Invention) However, in the impulse hammering method described in (1) above, the impulse generator is expensive, and in order to flow a large current even for a short time, for example, various parts of the armature may overheat. This causes stress such as changes in the shape and material due to the impact.Furthermore, there are various disadvantages such as the time and effort required for measurement.Furthermore, the above method (2) of hammering sound check by experts requires expensive equipment. Although it has the advantage of not causing stress or the stress mentioned above, it has disadvantages such as the evaluation is qualitative and ambiguous, the slack due to deadness of the coil inside the core cannot be detected, and the measurement is time-consuming. .

This invention was made in view of these conventional problems, and aims to solve the above problems by applying a vibration meter to the outside of the stator during operation to measure vibrations. .

[Means for Solving the Problem] In order to achieve the above object, the present invention provides a method for diagnosing the slackness of a stator coil of an AC motor, in which vibrations generated by the slackness of the stator coil are detected from the outside of the stator. AC motor stator coil that measures, then frequency-analyzes the measured data, and determines the degree of slack of the stator coil based on the power frequency and a vibration value twice the power frequency among the frequency components. A method for diagnosing slackness is provided.

[Effect]

In the present invention, when vibration was measured by placing a vibration meter on the outside of the stator during operation, it was found that the vibration generated by the electromagnetic force due to the alternating magnetic flux of the coil during operation propagated through the stator and frame. By data processing the power supply frequency and frequency components twice the power supply frequency among vibrations,
It was found that the degree of slack in the coil can be determined.

Therefore, the present invention measures the vibration (displacement) on the outside of the stator, performs frequency analysis on the measured data, and extracts the power frequency and twice the power frequency from among the frequency components using, for example, a band-pass filter. By extracting and processing this data, coil slack can be quantified.

〔Example〕

Hereinafter, the present invention will be explained with reference to the drawings. FIG. 1 is an explanatory diagram showing a diagnostic method according to the present invention, in which a vibration meter 7 is applied from outside to a stator 6 of an AC motor to measure vibrations.

At this time, in order to keep the measurement conditions constant, it is preferable to measure when the AC motor is idling, that is, when there is no load. 11 indicates a rotor.

Next, the measured vibration data is analyzed by the frequency analyzer 8, and the measurement mode at this time is "displacement".
shall be. Furthermore, from among the frequency components sent from the frequency analyzer 8, a bandpass filter 9 extracts the power supply frequency and twice the power supply frequency. The vibration values at this time are μ, respectively.

When μZt+ is assumed, the degree of coil slack is quantified by the following equation in the next coil slack calculation circuit 1o.

Coil slack evaluation value W = ・μ、102 ・μ2
f, where the displacement component μ of the power supply frequency represents the vibration value due to the slackness of the coil conductor 1a shown in Fig. 2, and μ2f is due to the slackness of the two upper and lower coil conductors 1a, Represents mutual vibration value.

That is, μ2f is a component that occurs when the degree of coil slack is significant, and the influence coefficient is corrected by (K,>K,) to improve the accuracy of coil slack evaluation (W).

Tables 11 and 2 below show examples of the diagnoses that were actually performed.

The AC motors used at this time were one 2500KW synchronous motor and three 6000KW synchronous motors, and vibrations were measured on the outside of the stator during idling.
When the degree of coil slack was calculated from the displacement component of 007, there was a strong correlation with the wedge slack rate determined by the conventional hammering sound check method (see Tables 1 and 2 below).

In addition, for the 2500 synchronous motor, all wedges were replaced, and the changes before and after replacement were confirmed as shown in Table 2.

In the above example, wedge slack, which indirectly indicates coil slack, was shown as comparative data.

Further, Table 1 shown below is a comparison table between the diagnosis results according to the present invention and the results according to the conventional method, and Table 2 is a table showing changes before and after all wedges in a 2500 KW synchronous machine were replaced.

〔Effect of the invention〕

As described above, according to the present invention, diagnosis can be performed without getting close to the rotating parts during operation, and therefore diagnosis can be easily performed without being constrained by measurement opportunities. As a result, it is no longer necessary to stop operations for several days every 5 to 10 years to perform diagnosis, as was the case in the past.

Furthermore, unlike the conventional impulse hammering method, it does not put stress on the armature and the equipment is inexpensive, and there is no variation in judgment results between individuals as in the case of hammering sound checks performed by experts. Because it is possible to detect when the coil insulation has withered, abnormalities can be detected before dielectric breakdown occurs, and unexpected accidents can be prevented.

Table 1 Table 2

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing a diagnostic method according to the present invention, and FIG. 2 is a partial sectional view of a stator of an AC motor. 1... Stator coil, 7... Vibration meter, 8... Frequency analyzer.

Claims (1)

[Claims] (1) In the method of diagnosing the slackness of the stator coil of an AC motor, the vibrations generated by the slackness of the stator coil are measured from the outside of the stator, and then the measured data is frequency-analyzed to determine the frequency component. A method for diagnosing stator coil slack in an AC motor, characterized in that the degree of slack in the stator coil is determined based on a power supply frequency and a vibration value twice the power supply frequency.