RU1805531C - Method for diagnosis of electric motor sliding contact - Google Patents

Description

The invention relates to the field of electrical engineering, in particular to means for non-destructive testing of electric motors.

The purpose of the invention is to increase the reliability of diagnosis.

The essence of the method is as follows. In the presence of contact defects at the places of defects, a transient resistance is formed, which has a random character. This leads to an increase in the intensity of contact sparking and an increase in the power of electromagnetic radiation caused by sparking. The power of electromagnetic radiation increases with increasing intensity of sparking and with increasing power of individual bits. However, the intensity of sparking cannot serve as an objective source of information about the presence of defects. (By intensity is meant the number of bits per unit time). A more objective characteristic of the state of the contacts is the degree of sparking, which is visually determined by observing the working sliding contact and using the value of the radiated power.

At the same time, point defects on the surface of the contacting surfaces lead to an increase in the duration of individual discharge pulses and, as a consequence, to an increase in the dispersion and, accordingly, the standard deviation of the discharge time. Taking into account the last interconnection can significantly increase the reliability of the diagnosis of a sliding contact. Indeed, an increase in the duration of individual bits

§

with ate

W

does not significantly increase the radiation power. At the same time, the dispersion of fluctuations in the discharge time increases quite strongly. Therefore, the reliability of the proposed method increases both in comparison with the count of pulses, and in comparison with a visual determination of the degree of sparking.

In order to take into account the latter factor, low-frequency components / amplitude of which is proportional to the duration of the discharge, are extracted from the spectrum of the received electromagnetic radiation. this records the average value of U and the standard deviation 7U of the received signal. Their ratio is practically independent of fluctuations in the number of discharge pulses, but it substantially depends on fluctuations in the duration of discharge pulses.

Therefore, the parameter

7i

tg

0)

can be selected as informative and by its value it is possible to judge the state of the sliding contact for its diagnosis.

Figure 1 shows a flowchart for implementing a method where the following notation is adopted: 1 - antenna (receiving); 2 - pre-amplifier; 3 - filter with a band (10 + 100) kHz; 4 - adjustable amplifier; 5 - detector; 6 - integrator; 7 - differential amplifier; 8 - quadratic voltmeter.

The scheme works as follows. The spark discharge radiation of the sliding contact of the tested electric motor (not shown in the diagram) is received by the antenna 1, amplified by a preliminary broadband amplifier 2, filtered by a filter 3. The gain control of the amplifier 4 ensures the normal operation of the remaining devices. The signal amplified by amplifier 4 is detected by detector 5 and averaged by integrator 6. The signal coming from integrator 6 to differential amplifier 1 is equal to the average value of the low-frequency component of the received electromagnetic radiation. A fluctuating voltage signal is output from the output of amplifier 4 to the second input of differential amplifier 7. At the output of the differential amplifier, a difference signal is generated. A quadratic voltmeter 8 measures its standard deviation. According to the indicators of the integrator 6 and the quadratic voltmeter 7, the values of U and GHz are set, respectively.

0

5

0

5

0

5

The integration time of integrator 6 is determined by

„1 t - -1-

Tng

where W is the lower boundary frequency of the filter 3.

The choice of the frequency band of filter 3 is determined on the one hand by selection from background noise prevailing at frequencies below 10 kHz, and on the other hand, by the requirement to eliminate the upper frequencies in the spectrum of the received electromagnetic radiation.

An example of a practical implementation of the method is shown in figure 2. Curve 9 corresponds to a change in parameter d) depending on the degree of spark n for the DP M-25-HI engine; curve 10 is a relative change (N / N0) in the number of discharge pulses at different degrees of sparking, wherein N0 corresponds to a degree of sparking of 1.25.

From figure 2 directly follows the increase in the reliability of the proposed method and the achievement by the operations of the method of the object of the invention. The operations of the method are as follows: they experience a limited selection of electric motors per service life; during the tests, the informative parameter TJ is periodically determined for each electric motor; set the average threshold j / n. preceding the failure of the sliding contact and its standard deviation a p.

li

Obviously -

(2)

where r} in is the individual threshold value of the informative parameter of the 1st electric motor;

k is the number of tested electric motors.

In this case, the standard deviation is

t

,) rr.

(3)

As a threshold value during operation, choose the value

pe tJn-Orj. (4)

During operation, the average value of the recorded signal U and its standard deviation Oc are periodically measured.

The value of / g; and / U are determined as it approaches the value of tj Pe. conclude that it is necessary to repair the sliding contact or replace the motor.

The application of the proposed method provides reliable detection of wear of the sliding contact and its timely repair. This prevents the sudden failure of the motor, ensures the timely introduction of redundancy, and thereby significantly saves material resources from the sudden downtime of expensive equipment.

Claims (1)

SUMMARY OF THE INVENTION A method for diagnosing a sliding contact of an electric motor, the method comprising 0 receiving signals of electromagnetic radiation from spark discharges, generating counting pulses and comparing the number of received pulses over a certain period of time with a given number of pulses, characterized in that that, in order to increase the reliability of the diagnosis, the low-frequency component of the received signal is extracted, its mean value and standard deviation are measured, the ratio of standard deviation to mean value is determined and compared with the set value. Fig /