RU90199U1 - DIAGNOSTIC DEVICE FOR AC ELECTRIC MOTORS AND MECHANICAL EQUIPMENT ASSOCIATED WITH THEM - Google Patents

Abstract

Diagnostic device for AC electric motors and associated mechanical equipment, consisting of a housing with external connectors for measuring vibration emitted by an electric motor along three axes, and located inside the housing by a measuring unit with an analog-to-digital converter (ADC) and a personal computer, characterized in that the device case is sealed, and the analog-to-digital converter is connected to the outputs of the sensors through a multiplexer.

Description

A method for the diagnosis of AC electric motors and associated mechanical equipment and a device for realizing it.

The invention relates to the field of operation of technical equipment, mainly AC electric motors and associated mechanical equipment.

A known method for the diagnosis of mechanical devices, mainly pneumohydraulic units and pipelines, including measuring before operation, and determining the real technical condition of the equipment during operation (see patent of the Russian Federation 2253096, IPC ⁷ G01M 15/00, F15 B 19/00, publication from May 27, 2005) - [1].

The disadvantages of this method is its use mainly for pneumohydraulic units and pipelines, as well as the lack of indication of specific diagnostic parameters necessary to determine the real technical condition of the equipment during operation.

A known method for the diagnosis of mechanical devices, namely rolling bearings and a device for its implementation, including a test bench, measurement of diagnosed parameters and comparison with similar results of "reference *** bearings (see application for invention of the Russian Federation 2004108229, IPC ⁷ С01М 13/04, publication of October 20, 2005) - [2].

The disadvantages of this method is the installation of bearings in the portable equipment of the test bench, for which it is necessary to disassemble the diagnosed equipment, and this method is applicable only to one element of the diagnosed equipment - the rolling bearing.

A known method for the diagnosis of mechanical devices, namely rolling bearings, including measuring the vibration of the diagnosed bearing and determining its technical condition (see application for invention of the Russian Federation 2003124988, IPC ⁷ G01M 13/04, publication of 02/10/2005) - [3].

The disadvantage of this method is its applicability only to determine the technical condition of rolling bearings, excluding the rest of the equipment.

There is a known method for diagnosing machinery, including placing an oversized microphone in the area of the diagnosed node, removing the electrical signal from the microphone output, extracting from this signal an information parameter that determines the level of origin and development of the defect (see patent of the Russian Federation 2090853, IPC ⁷ G01M 17 / 00, publication of September 20, 1997) - [4].

The disadvantage of this method is the use of a microphone as a sensor, the readings of which can be influenced by the state of the environment.

A known method for the diagnosis of electrical equipment, including the impact on the structure by the pathogen of vibration and the assessment of the response signal of the structure, as the response signal, record the spectral density of the vibration power resulting from vibration exposure, and determine the shape of the spectral density of the vibration power (see application for invention RF 2003120314, IPC ⁷ G01N 7/00, publication of January 10, 2005) - [5].

The disadvantage of this method is the use of additional equipment to excite vibration, and as a result, stop the diagnosed equipment.

A known method for diagnosing equipment, including spectral analysis of the forced acoustic response memory of emission-adsorption structural changes (see application for invention of the Russian Federation 2003134817, IPC ⁷ G01N 29/14, publication of 05/10/2005) - [6].

The disadvantage of this method is its use for predicting the residual life of the equipment metal, which is applicable for the visible parts of equipment elements, and for diagnosing the elements inside the equipment, it becomes necessary to parse the diagnosed equipment, and this method is possible only with the use of additional equipment - a vibration exciter.

The prototype of the invention is a method for diagnosing AC electric motors and related mechanical devices, in which during a given time interval they measure and record values, using sensors, convert the received signal from analog to digital, perform a spectral analysis of the received signal and compare the values amplitudes at characteristic frequencies, measurements and their analysis are carried out with a certain periodicity, they create a database from which they control the development of damage over time and determine the residual life of the equipment (see application for invention of the Russian Federation 2005110648, IPC ⁷ G01R 31/34, publication of 10/20/2006) - [7].

The disadvantage of this method is the need to stop the diagnosed equipment, partial disassembly for connecting sensors, which can lead to errors in the repair personnel and reduce the life of the equipment up to 30%.

The problem solved by the invention is as follows: diagnostics of alternating current electric motors and associated mechanical equipment using the CIP method, without shutting down the diagnosed equipment.

This problem is solved by the fact that during a given time interval, the values of the vibration signal emitted by the electric motor are measured in three axes using the appropriate vibration sensors, the readings of which are recorded through an analog-to-digital converter on a personal computer storage device, spectral analysis of the received signal is made and comparison values of amplitudes at characteristic frequencies, measurements and their analysis are carried out with a certain frequency, create from them ba from the data on which control the development of lesions in time and determining the remaining service life of equipment, while the measurements are made indiscriminately diagnosed operating equipment, via an external sensor mounting on the casing.

A device for implementing the proposed method contains external vibration sensors attached to the body of the diagnosed equipment using external holders, a sealed case with a personal computer, an analog-to-digital converter and a multiplexer with separate inputs of the analog-to-digital converter, and connectors for connecting vibration measurement sensors emitted by the electric motor in three axes.

When developing the presented method, studies of operational reliability were carried out, which are the basis for solving the above problems. The studies were conducted in two main directions, namely, retrospective and structural-type analysis. A retrospective analysis aimed to identify patterns of aging and damage to components and elements of electric motors. Structural-type analysis - determination of the least reliable components and elements of electric motors.

As the analysis showed, the role of repair personnel in maintaining reliable and safe operation of power supply systems is important. Reducing violations due to the fault of the repair personnel, reducing the repair time directly leads to increased reliability.

In 2002, the proportion of disruptions in the operation of power supply systems through the fault of personnel was 39%. A third of them occurred through the fault of the repair staff.

If we consider the distribution of violations among repair production sites, then the share of the production site for the repair of electric motors accounts for 40.3%, the section for the repair of complete switchgear - 6 / 0.4 kV - 26.8%, and the site for the repair of open distribution devices - 330/750 kV - 21.9%. The remaining repair sites account for less than 10%.

The distribution of violations by type of equipment showed that the largest number of violations occurred in switchgear — 44%, electric motors — 34%, transformers and reactors — 8%, and turbine generators — 4%. The first two types of equipment account for about 80% of violations.

Distribution of violations due to fault of repair and maintenance personnel on electric motors, taking into account the voltage level: 0.4 kV - 60.5%, 6 kV - 39.5%. According to the nodes of the electric motor: input box - 38.4%, adapter box of clamps - 26.1%, bearing units - 16.7%, stator winding - 12%, other units - 7%.

The analysis showed that the largest number of violations in the operation of electrical equipment (44.7%) is associated with damage to electrical contact connections (poor contact, open circuit).

Frequently encountered causes of motor failures, according to acts of investigation of workshop failures account for 55.2%, is classified as poor repair.

This is followed by maintenance errors (11.4%).

It should be noted that some acts do not indicate what exactly poor repair or maintenance was expressed in, which, in turn, does not allow for a more in-depth analysis of the causes and the development of adequate measures to prevent violations.

The next reason for violations (11.4%) is negligence, carelessness, excessive self-confidence. Example: when tested according to the coca schedule, the reverse rotation of the unit was revealed. Upon examination, it was found that the phases were reversed when the power cable was connected.

Then there are poor-quality adjustment or its failure, violation of the terms (periodicity) of the repair, the performance of maintenance and repair not in full, respectively, 7.8%, 5.7% and 3.2%.

The deficiencies in control of acts account for 3.2%. This figure also seems to be underestimated, since a significant part of the violations could have been avoided by monitoring the implementation of responsible repair operations and carefully accepting equipment from repair.

Based on the foregoing, it is clear that, recently, all enterprises are forced to look for ways to improve the efficiency of their repair services. The best results are obtained during the transition from the equipment maintenance system - scheduled preventive repairs (NDP) to the technical maintenance service system. It is known that you should not disassemble and repair still good equipment. Simple disassembly and assembly of equipment, even without replacing parts, can reduce its life by 30 percent. There is also no guarantee that you will install the best quality components during the repair. And if we take into account the inevitable after-repair run-in of the units of the unit, then instead of benefit it will be ... But you cannot put off the necessary repairs. Usually, all defects tend to further self-development, expanding to a whole range of reasons, one of which ultimately leads to an emergency stop of the units. The cheapest and fastest repair is the timely elimination of the root cause of the accident. This is achieved through an operational assessment of the current technical condition of the equipment, timely detection of defects, optimal planning of the timing of repairs, all of these questions are answered by the vibration diagnostics of rotating equipment. Vibration is the most universal parameter that takes into account almost all aspects of the state of the unit, which allows it to "determine" in working conditions to determine the technical condition of the equipment. The main purpose of vibration diagnostics is the implementation of the equipment maintenance system according to the actual technical condition, according to which maintenance is carried out only in the case and in the place where it is absolutely necessary. The basis for determining the current state of the equipment is the measurement of the rms value (RMS) of the vibration velocity (mm / s) in the range from 10 to 1000 Hz in three directions - “Vertical”, “Cross” (“Horizontal”) and “Axial”. Comparison of the measured values with the standard allows you to assess the state of the unit. The choice of such a unit of measurement is due to the presence of a number of Russian and international norms and recommendations on permissible vibration levels (in units of vibration velocity) for various types of equipment, for example, ISO 2372 recommendations. In these recommendations, the values of the maximum vibration level depend on the engine power of the unit, on the number of shaft revolutions unit, depending on the type of foundation. At the same time, these recommendations do not take into account the installation conditions of each unit, operating and maintenance conditions, technological load, operating life, etc. Carrying out works on vibration diagnostics gives a real economic effect, as it helps:

- an increase in time between repairs - and as a result, this is an increase in productivity and a decrease in the cost of repairs;

- prevention of predicted breakdowns - which contributes to increased reliability;

- elimination of secondary breakdowns, for example, gearbox breakdowns due to bearing malfunctions;

- elimination of unnecessary consumption of parts, the exclusion of the replacement of still serviceable parts;

- reducing the volume of spare parts, as the nomenclature and quantity of necessary parts and spare parts are known in advance;

- reducing the total duration of the repair work, because All necessary work is planned in advance.

Analysis of failure statistics of electric motors showed that:

- 46.8% of motor failures occur as a result of failures in the bearing units;

- 33.6% of failures due to a malfunction in the stator winding;

- 5.5% of failures cause misalignment;

- 4.0% failed due to the bending of the paws of the electric motors (a generic name that includes both the curvature of the paws themselves and various deformations of the frames on which the units are mounted);

- 3.2% of failures provoked defects in the couplings;

- 6.9% of electric motors fail due to a failure of other components (imbalance of the rotor of the unit, insufficient rigidity of the mounting of the unit, wear of the bearing housing with the pump housing, physical wear of the equipment, skew axis of the shaft line, structural resonance, corrosion-erosion wear.

As can be seen from the above analysis, the most common type of malfunctions are - violations in the bearing assemblies. This type of malfunction can be caused by the following factors:

- defects in the outer ring of the bearing;

- defects on the inner ring of the bearing;

- defects in rolling elements;

- violation of lubrication.

As a result of theoretical and experimental studies, expressions were obtained for calculating the frequencies of reflecting factors causing disturbances in the bearing assemblies.

To calculate the frequency of vibration with defects in the outer ring of the bearing, the expression is used:

where D _B is the diameter of the inner ring;

D _H is the diameter of the outer ring;

N is the number of rolling bodies;

f _p - frequency of rotation of the rotor of the electric motor.

Defects in the inner ring of the bearing appear at a frequency calculated by the formula:

The frequency reflecting the defects of the rolling elements is determined by the formula:

where D _W - the diameter of the rolling elements.

If the lubrication of the bearing is impaired, an increase in the amplitude of vibration is observed at all of the above frequencies simultaneously.

Vibration of the electric motor directly depends on the torque in the electric motor. Since other types of malfunctions (malfunctions in the stator winding, misalignment, bending of the legs of the electric motors, defects in the couplings) affect the torque, they cause a change in the vibration of the electric motors.

Torque in an asynchronous machine is created as a result of the interaction of a rotating field and currents induced by it in the rotor winding. Its value can be found on the basis of the law of electromagnetic forces, the torque is equal to ([8] - See chapter 3, § 3-13):

where B _M is the maximum induction in the air gap, all / cm ² ;

l is the active length of the conductor, cm;

N is the number of stator winding conductors;

D 'is the diameter of the rotor;

Ψ ₂ is the shift between B _M and I _2M (in electric radians);

I _2M maximum current of the rotor circuit. As:

where i ₁ is the current in the stator winding of the electric motor;

ω ₁ - the number of turns in the winding;

l is the active length of the conductor;

Where

where E ₂ - emf in the winding of the rotor of the electric motor;

r ₂ is the active resistance of the rotor winding;

x ² - inductive resistance of the rotor winding;

s is the working slip.

Comparing the types of malfunctions with the above formulas, it is seen that:

- malfunctions in the stator winding affect the torque due to a change in the number of conductors in the stator winding (N), the active length of the conductor (l) and changes in the maximum induction in the air gap (B _M );

- misalignment and defects in the couplings have an effect due to a change in the load on the motor shaft and, consequently, changes in the working slip (s);

- the bending of the paws of the electric motors leads to a change in the air gap between the stator winding and the rotor, which leads to a change in the maximum induction in the air gap (B _M ) and, as a consequence, to a change in the torque M

In order to determine the frequencies at which faults manifest themselves, it is necessary to consider the torque as a function of time. As a result of theoretical and experimental studies, expressions were obtained for calculating the frequencies of reflecting types of malfunctions of electric motors.

To determine the presence of inter-turn faults, it is necessary to analyze at a frequency determined by the formula:

where f _U is the frequency of the supply network;

k are the coefficients determined by the rotor speed;

s is the working slip;

p is the number of pole pairs.

Alignment and defects in the couplings are determined at frequencies calculated by the formula:

The bend of the paws of electric motors manifests itself at a frequency calculated by the formula:

Failures of the driven equipment manifest themselves at the characteristic blade frequency, which is determined as follows:

where f _l - the frequency of rotation of the impeller;

Zl - the number of impeller blades.

Vibration measurement is carried out with a certain periodicity, from the obtained data create a database, determine the residual life and form a plan for technical inspection and repair of equipment based on data on the actual technical condition of the equipment.

Figure 1 schematically shows a schematic diagram of a device that implements the method.

Figure 2 is a photograph of a device that implements the method. A device for implementing the proposed method (Fig. 1) contains external vibration sensors 1 along three axes (1a, 1c and 1 s), a sealed housing 2 with a personal computer 3, an analog-to-digital converter 4 and a multiplexer with separate inputs of an analog-to-digital converter 5, and connectors for connecting vibration measurement sensors emitted by the electric motor along three axes 6, as well as the diagnosed electric motor 7 with equipment 8.

A device that implements the above method works as follows: measured over a specified time interval of the values of the vibration signal emitted by the electric motor 7 in three axes, using the appropriate external vibration sensors 1 (1a, 1c and 1 s) connected to the connectors 6, then through the multiplexer 5, the signal is transmitted to an analog-to-digital converter 4 and after converting the signal from an analog form to digital, it is transmitted to a portable computer 3, where the signal is recorded on a read-only memory roystvo followed by treatment consisting of a fast Fourier transform weighted spectral bands windowed informative over separate frequencies.

Thus: the proposed method allows to determine the presence of malfunctions of electric motors and related equipment, including incipient malfunctions, in-place diagnosis of the electric motor and related equipment using the developed device. This makes it possible to determine the actual technical condition of electric motors and related equipment in real time with different operating modes of its operation, which reduces the cost of maintenance and technical repair by eliminating incipient malfunctions and simplified maintenance of serviceable equipment.

The above set of features according to the claims is not currently known from the prior art and does not follow from the well-known rules for the diagnosis of AC electric motors and associated mechanical equipment, this proves compliance with the criterion of "inventive step".

The proposed method and device realizing it are new for the diagnosis of AC electric motors and related equipment, which meets the criteria of the invention: "novelty."

The constructive implementation of the device diagnosing AC electric motors and associated mechanical equipment with the indicated set of essential features does not present any structural, technical and technological difficulties, hence the compliance with the criterion of "industrial applicability" follows.

Literature

1. Pat. RF №2253096 dated 05/27/2005, class G01M 15/00, F15B 19/00 (Method for assessing the technical condition of equipment).

2. Application for the invention of the Russian Federation No. 2004108229, dated 10.20.2005, class. G01M 13/04 (Method for the comprehensive diagnosis of rolling bearings and a device for its implementation).

3. Application for the invention of the Russian Federation No. 2003124988, dated 10.02.2005, class. G01M 13/04 (Method for the diagnosis of rolling bearings).

4. Pat. RF №2090853 from 09.20.1997, class G01M 17/00 (Method for vibro-acoustic diagnostics of machinery).

5. Application for the invention of the Russian Federation No. 2003120314 of 01/10/2005, class. G01N 7/00 (Method for the diagnosis of electrical equipment).

6. Application for the invention of the Russian Federation No. 2003134817 from 05/10/2005, class. G01N 29/14 (Method for predicting the residual life by non-destructive testing in the examination of industrial safety of equipment).

7. Application for the invention of the Russian Federation No. 2005110648 from 10.20.2006, class. G01R 31/34 (Method for the diagnosis of AC electric motors and related mechanical devices) - prototype.

8. P.S. Sergeev. Electric cars. Textbook for high schools. // Moscow.

Claims (1)

Diagnostic device for AC electric motors and related mechanical equipment, consisting of a housing with external connectors for measuring vibration emitted by an electric motor along three axes, and located inside the housing by a measuring unit with an analog-to-digital converter (ADC) and a personal computer, characterized in that the device case is sealed, and the analog-to-digital converter is connected to the outputs of the sensors through a multiplexer.