Method for non-destructive acoustic testing of ceramic post insulators

Abstract

A method for the non-destructive acoustic testing of the mechanical strength of a ceramic post insulator includes exciting natural vibrations in an insulator, converting the natural vibrations into an electrical signal, recording said signal on a machine-readable carrier, calculating the energy spectrum of the signal in the tested frequency band, and checking that the calculated energy spectrum meets set diagnostic criteria. The insulator is declared fit for use if the maximum value of the energy spectrum in each of the frequency ranges 1.0-1.3 kHz and 9.7-10.0 kHz does not exceed 10% of the global maximum of the energy spectrum of the natural vibrations of the insulator. The technical result consists in reducing the probability of error when establishing whether an insulator is fit for continued use.

Description

[0001] Method of non-destructive acoustic testing of ceramic support-rod insulators

[0002] Field of technology

[0003] The invention relates to the field of electric power engineering, namely to methods of non-destructive acoustic testing of the technical condition of ceramic (porcelain) support-rod insulators, both single and assembled in columns, and can be used to check the load-bearing capacity of such insulators equipped with temperature-compensating elements.

[0004] State of the art

[0005] The mechanical strength and, accordingly, the load-bearing capacity of ceramic support insulators, widely used in electrical equipment of various voltage classes, decreases during their service life due to defects that arise under the influence of climatic factors (moisture, temperature changes with freezing and thawing of moisture), mechanical loads, as well as due to violations and imperfections in manufacturing technology.

[0006] The value of the minimum destructive load of a defect-free insulator is given in its factory passport, as a rule, with a two-threefold design reserve. Therefore, the insulator is recognized as unfit for operation only if there is reason to believe that the existing defect reduces the bearing capacity of the insulator to a critical level - the above-mentioned passport value of the minimum destructive load. Timely diagnosis of such a critical defect is the main task of non-destructive acoustic testing of a ceramic support-rod insulator.

[0007] Ceramic (porcelain) support-rod insulators of modern designs are equipped with elastic temperature-compensating elements adjacent to the reinforcement seams between the ceramic rod and metal flanges (GOST R 52034-2008. Ceramic support insulators for voltages over 1000 V. General specifications). In this regard, the energy spectra of natural (resonant) oscillations of such insulators differ significantly from similar spectra of support-rod insulators that do not have elastic temperature-compensating elements.

[0008] A method of non-destructive acoustic testing of a ceramic support-rod insulator is known, according to which, upon the appearance or absence in the energy spectrum of the insulator’s natural oscillations of at least one additional peak, comparable in level to the peak of the fundamental tone, a conclusion is made about the unsatisfactory or satisfactory condition of the insulator, respectively [RU2275647].

[0009] The disadvantages of this method are that:

[0010] - the method is not applicable for testing insulators whose energy spectra have several fundamental tones (columns of several insulators or insulators with temperature-compensating elements), since it leads to false rejections of such insulators;

[0011] - the absence of numerical criteria leads to subjective assessments of the insulators' condition and does not allow the use of software and algorithmic analysis of the energy spectrum to obtain objective and reliable testing results. A method of non-destructive acoustic testing of the mechanical strength of a ceramic support-rod insulator is known, disclosed in the source "Mobile indicator complex models MIK-1 and MIK-2.

[0012] Methodological instructions”, available on the applicant’s website for ccbuiKe[https: / / logoteh.ru / wp-content / uploads / 2019 / 07 / %D0%9C%D0%A3_%D0%9C%D0%98%D0%9A_% D0%A0%D0% A4-2019.pdf].

[0013] The method has a variant (p. 6.2 of the specified source, pp. 37-44), intended for testing ceramic support-rod insulators of modern design, equipped with temperature-compensating elements. This variant of the known method is adopted as a prototype.

[0014] The prototype method includes excitation of natural (resonant) oscillations of the insulator, calculation and registration of the energy spectrum of these oscillations in the controlled frequency band of 1.0-10.0 kHz and verification of the energy spectrum's compliance with the specified diagnostic criteria for the insulator's suitability for operation (verification of compliance with the rejection criteria).

[0015] The prototype method uses the fitness criteria in the form of qualitative assessments of four main peaks of the energy spectrum located in four frequency ranges (1.4-2.0; 3.2-4.8; 4.5-7.5; 7.5-9.5 kHz). Unsuitability for operation caused by a decrease in the bearing capacity of the insulator to a critical level is diagnosed according to the prototype method in the event of a shift of two main peaks of the specified extreme ranges to the boundaries of the controlled frequency band, and two other main peaks - to the range of 4.0-5.0 kHz. In addition, the unsuitability of the insulator is diagnosed by the prototype in the event of the appearance of multiple additional peaks in the frequency range of 6.5-9.5 kHz. The specialized software (SSP) of the prototype calculates the energy spectrum of excited oscillations in the controlled frequency band and displays it on the display, and the compliance of the calculated energy spectrum with the specified diagnostic fitness criteria is checked visually.

[0016] The disadvantage of the prototype is the low reliability and subjectivity of the control results, due to the multiplicity, vagueness and ambiguity of the suitability criteria, the absence of numerical values ​​of the main and additional peaks of the energy spectrum and, accordingly, the impossibility of software and algorithmic analysis of the obtained energy spectrum.

[0017] The essence of the invention

[0018] The technical result of the invention is an increase in the objectivity and reliability of control, a corresponding decrease in the probability of error in establishing the suitability of an insulator for further operation, as well as the possibility of automating the diagnostic stage of control due to software and algorithmic analysis of the energy spectrum of the insulator's natural oscillations. The consequence of this is a simplification of maintenance and an increase in the operational safety of high-voltage electrical equipment containing ceramic support-rod insulators (both single and assembled in columns), equipped with temperature-compensating elements.

[0019] This was achieved by using a single and unambiguously digitized criterion of suitability, which was found as a result of statistical processing of a set of energy spectra obtained during natural tests of insulators, and additionally confirmed by numerical experiments on mathematical models of a single support-rod insulator and a column of such insulators.The subject of the invention is a method for non-destructive acoustic testing of the mechanical strength of a ceramic support-rod insulator, including excitation of the insulator's natural oscillations, calculation and recording of their energy spectrum in a controlled frequency band and verification of the compliance of the calculated energy spectrum with specified diagnostic criteria, characterized in that the insulator is recognized as fit for operation if the energy spectrum of its natural oscillations satisfies the first diagnostic criterion, consisting in the fact that the maximum value of the energy spectrum in each of the frequency ranges of 1.0-1.3 kHz and 9.7-10.0 kHz does not exceed 10% of the global maximum of the energy spectrum of the insulator's natural oscillations in the controlled frequency band.

[0020] The invention has developments, the first of which consists in that the insulator recognized as fit for operation is re-tested at the opposite sign of the ambient temperature, the insulator repeatedly recognized as fit for operation is tested for the third time after the sign of the ambient temperature returns to the initial value, and the insulator recognized as fit for operation for the third time is classified as defect-free if the energy spectrum of its natural oscillations satisfies the second, third and fourth criteria, of which the second consists in that the local maximum of the energy spectrum in each of the four frequency ranges of 1.3-3.0 kHz, 3.0-5.5 kHz, 5.5-8.0 kHz and 8.0-9.7 kHz exceeds 5% of the global maximum of the energy spectrum in the monitored frequency band at a positive oscillation fixation temperature and at least in the range of 3.0-5.5 kHz at a negative oscillation fixation temperature, the third criterion consists in that,that the local maxima of the energy spectrum of adjacent of the four specified frequency ranges are separated from each other by intervals of at least 1.0 kHz, in which the local minima do not exceed 5% of the global maximum in the monitored frequency band, and the fourth is that the frequencies of the specified local maxima and minima coincide with the corresponding frequencies of the energy spectrum of the insulator's natural oscillations, previously recorded at a temperature of the same sign.

[0021] The second development of the invention consists in that the insulator is classified as having an admissible non-developing defect if the energy spectrum of its natural oscillations satisfies the second and fourth criteria, but does not satisfy the third criterion, or as having an admissible developing defect if the said energy spectrum satisfies the second and third criteria, but does not satisfy the fourth criterion.

[0022] These developments allow us to divide insulators that remain in operation into three groups in accordance with the optimal tactics for further maintenance in terms of labor costs:

[0023] - defect-free;

[0024] - with an acceptable non-developing defect;

[0025] -with an acceptable developing defect.

[0026] The invention has another development, which clarifies the fourth (comparative) criterion and reduces the probability of error in diagnostics according to this criterion, consisting in the fact that frequencies whose difference does not exceed 50 Hz are considered to be coinciding.

[0027] Brief description of the figures

[0028] Fig. 1-6 show examples of energy spectra of natural oscillations of ceramic support-rod insulators. The spectra are shown in logarithmic scale and normalized by the global maximum in the controlled frequency band of 1.0-10.0 kHz. The spectra in Fig. 1 and 2 refer to oscillations recorded, respectively, at positive and negative temperatures on defective insulators subject to decommissioning. The spectra in Fig. 3 and 4 refer to oscillations recorded, respectively, at positive and negative temperatures on defect-free insulators. The spectra in Fig. 5 and bot refer to oscillations recorded, respectively, at positive and negative temperatures on insulators having a defect acceptable for operation.

[0029] Implementation of the invention taking into account its developments

[0030] The procedure for monitoring the insulator using the claimed method, taking into account its developments, can be divided into two stages:

[0031] - monitoring, including excitation of the insulator's natural oscillations, their conversion into an electrical signal with recording on a machine-readable medium, calculation of the energy spectrum of the recorded oscillations in the monitored frequency band (for example, using the mathematical procedure of fast Fourier transform) and its registration (i.e. saving the energy spectrum in computer memory or on a machine-readable medium with an indication of the insulator identifier, date and ambient temperature in °C);

[0032] - diagnostics of the insulator condition by comparing the obtained energy spectrum and the specified diagnostic criteria.

[0033] The monitoring stage, including the calculation of the energy spectrum of the natural oscillations of the monitored insulator, can be carried out, for example, using the mobile indicator complex MIK-2 similar to the monitoring stage described in detail in the source of the prototype. It is advisable (but not necessary) to supplement this stage with the operation of normalizing the energy spectrum, ensuring the convenience of subsequent comparison with universal (in relation to the types and examples of monitored insulators) digital values ​​of the diagnostic criteria. Normalization is advisable to be performed relative to the global maximum of the spectrum in the monitored frequency band, as is accepted in this description, or relative to another value with an equivalent recalculation of the compared values.

[0034] To carry out automatic diagnostics, the software package, available, for example, as part of the MIC-2 complex, must be supplemented with a software application that performs an analysis of the calculated spectrum in accordance with the claimed method.

[0035] The insulator condition is checked periodically, starting from its commissioning and until its decommissioning. The first check is carried out after commissioning, the second and subsequent ones - after the sign of the average daily ambient temperature on the Celsius scale has changed (i.e. after this temperature passes the freezing point of water / melting point of ice). At each check, the suitability of the insulator for further operation is checked using the first criterion. According to this criterion, the insulator is recognized as fit for operation if the maximum values ​​of the energy spectrum of its oscillations in each of the two frequency ranges of 1.0-1.3 kHz and 9.7-10.0 kHz do not exceed !0% of the global maximum of the energy spectrum in the monitored frequency band of 1.0 -10.0 kHz. An insulator that is not recognized as fit is subject to decommissioning.

[0036] During the initial and second inspections, the energy spectrum is checked only by the first criterion. The third and possible subsequent procedures of insulator inspection are carried out after the average daily ambient temperature has passed through zero on the Celsius scale, i.e., in the presence of an energy spectrum of oscillations previously recorded on the insulator under inspection at the same sign of the average daily temperature. This allows one to detect changes in the mechanical state of the insulator by comparing the energy spectra of the insulator's natural oscillations recorded at the same sign of the ambient temperature. Therefore, during the third and subsequent inspection procedures, it is advisable to supplement the diagnostics of the insulator left in operation by comparing such energy spectra. According to the development of the claimed method, such a comparison is performed using three criteria (the second, third, and fourth) in a complex, one of which (the fourth) is comparative. The set of criteria includes:

[0037] - the second criterion, which consists in the fact that the local maximum of the energy spectrum in each of the four frequency ranges 1.3-3.0 kHz, 3.0-5.5 kHz, 5.5-8.0 kHz and 8.0-9.7 kHz exceeds 5% of the global maximum of the energy spectrum in the monitored frequency band at a positive oscillation fixation temperature and, at least, in the range 3.0-5.5 kHz at a negative oscillation fixation temperature;

[0038] - the third criterion, which consists in the fact that the local maxima of adjacent of the four specified frequency ranges are separated from each other by intervals of at least 1.0 kHz, in each of which the energy spectrum has a local minimum of less than 5%;

[0039] - the fourth criterion, which can be characterized as comparative, is that the frequencies of the indicated maxima and minima coincide with the corresponding frequencies of the energy spectrum of the insulator’s natural oscillations, previously recorded at a temperature of the same sign.

[0040] The combined application of the second, third and fourth criteria allows us to classify an insulator that has been deemed suitable into one of three groups:

[0041] - defect-free insulators, if the energy spectrum of the insulator’s natural oscillations satisfies the second, third and fourth criteria;

[0042] - insulators with an acceptable non-developing defect, if the energy spectrum of the insulator’s natural oscillations satisfies the second and fourth criteria, but does not satisfy the third criterion;

[0043] - insulators with an acceptable developing defect if the energy spectrum of the insulator's natural oscillations satisfies the second and third criteria, but does not satisfy the fourth criterion.

[0044] Other combinations of the second, third and fourth criteria for monitoring insulators fit for use are not encountered in practice.

[0045] As can be seen from the above, the technical result of the invention is achieved after the initial testing, including excitation of the insulator's natural oscillations, their recording, calculation of the energy spectrum of the insulator's natural oscillations in the controlled frequency band and verification of the calculated energy spectrum's compliance with the specified diagnostic criterion. In this case, the specified result is achieved due to the fact that, when diagnosing the insulator, an unambiguous and numerically characterized first diagnostic criterion is used, which consists in the fact that the maximum value of the energy spectrum of the natural oscillations of the insulator fit for operation in each of the frequency ranges of 1.0-1.3 kHz and 9.7-10.0 kHz does not exceed 10% of the global maximum of the energy spectrum of the insulator's natural oscillations in the controlled frequency band.

[0046] Similar procedures for monitoring the mechanical strength of insulators in operation with the achievement of the above-mentioned technical result are also performed after subsequent transitions of the average daily air temperature through zero. In this case, after the second (reverse) transition of the average daily temperature through zero on the Celsius scale, it becomes possible to additionally apply a complex diagnostic criterion for assessing the insulator condition, consisting of the second, third and fourth criteria, one of which (the fourth) is comparative, to divide the insulators in operation into the three above-mentioned groups and reasonably establish an individual time interval for each insulator until the next mechanical strength monitoring.

Claims

Invention formula 1. A method for non-destructive acoustic testing of the mechanical strength of a ceramic support-rod insulator, including excitation of the insulator's natural oscillations, calculation and recording of their energy spectrum in a controlled frequency band, and verification of the calculated energy spectrum's compliance with specified diagnostic criteria, characterized in that the insulator is recognized as fit for operation if the energy spectrum of its natural oscillations satisfies the first diagnostic criterion, consisting in the fact that the maximum value of the energy spectrum in each of the frequency ranges of 1.0-1.3 kHz and 9.7-10.0 kHz does not exceed 10% of the global maximum of the energy spectrum of the insulator's natural oscillations in the controlled frequency band.

2. The method according to claim 1, characterized in that the insulator recognized as fit for operation is re-tested at the opposite sign of the ambient temperature, the insulator repeatedly recognized as fit for operation is tested for the third time after the sign of the ambient temperature returns to the initial value, and the insulator recognized as fit for operation for the third time is considered defect-free if the energy spectrum of its natural oscillations satisfies the second, third and fourth criteria, of which the second is that the local maximum of the energy spectrum in each of the four frequency ranges !, 3-3.0 kHz, 3.0-5.5 kHz, 5.5-8.0 kHz and 8.0-9.7 kHz exceeds 5% of the global maximum of the energy spectrum in the monitored frequency band at a positive oscillation recording temperature and, at least, in the range 3.0-5.5 kHz at a negative temperature fixation of oscillations, the third criterion is that the local maxima of the energy spectrum of the neighboring of the specified four frequency ranges are separated from each other by intervals of at least 1.0 kHz, in which local minima do not exceed 5% of the global maximum in the controlled frequency band, and the fourth is that the frequencies of the specified local maxima and minima coincide with the corresponding frequencies of the energy spectrum of the insulator's natural oscillations, previously recorded at a temperature of the same sign.

3. The method according to paragraph 2, characterized in that the insulator is classified as having an acceptable non-developing defect if the energy spectrum of its natural oscillations satisfies the second and fourth criteria, but does not satisfy the third criterion, or as having an acceptable developing defect if the said energy spectrum satisfies the second and third criteria, but does not satisfy the fourth criterion.

4. The method according to paragraph 2 or 3, characterized in that frequencies whose difference does not exceed 50 Hz are considered to be coinciding.

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