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Diagnosis of electric motors of pumping units based on the phase diagrams of vibration velocities and vibration acceleration

Keywords:

A.N. Akimov – Head of Department, JSC Academician M.F. Reshetnev «ISS» (Zheleznogorsk)
E-mail: akimov@iss-reshetnev.ru
A.M. Lepihin – Dr. Sc. (Eng.), Main Research Scientist, Institute of Computational Technologies of SB RAS (Krasnoyarsk)
E-mail: aml@ict.nsc.ru
R.W. Zelenov – Engineer, Institute of Computational Technologies of SB RAS (Krasnoyarsk)
E-mail: zelenov_r@mail.ru


The article presents the results of vibration diagnostics of rolling bearings of electric motors of pump units of spacecraft cooling systems. Failures and malfunctions of such bearings can lead to severe consequences, up to the termination of normal operation of on-board equipment. In this regard, a reliable system for diagnosing the technical condition of bearings is required.
Currently, there are a large number of different diagnostic devices and systems that are used in the process of vibration diagnostics. In these systems, the methods of statistical analysis of spectra and trends of vibration signals are laid. As the criteria characteristics, the mean square deviations, the peak factor, the cross factor and other vibration parameters are considered. Nevertheless, sufficient reliability of the results of vibrodiagnostics is provided only in the presence of developed defects, when the residual life of bearings is 20…40% of the guaranteed operating time. The detection and identification of bearing defects at the initial stage of their development remains a creative process, which until now has not been formalized.
The norms of permissible vibrations for the considered engines are absent. Therefore, it is extremely difficult to identify vibration frequencies to determine the type of defect or malfunction. A method for ranking the quality of electric motors based on the results of vibrodiagnostics with the construction of phase diagrams of «vibration velocity vibroacceleration» and «mean square deviation of vibration velocity is the mean square deviation of vibration acceleration» is proposed.
The object of control were the bearings of the electric motors of pump pumping units of the cooling systems of on-board apparatus of space vehicles. The electric motor is a three-phase synchronous machine, driven by an inductor. Vibrodiagnostics was carried out in idle and during operation in the pump unit. The SD-12M vibration analyzer performed the signal recording and processing. The vibration signals were recorded on the X, Y and Z axes for 30 minutes with a sampling frequency of 20480 at 5000 rpm and 6000 rpm, synchronously recording in three orthogonal directions using a three-axis accelerometer.
An analysis of the spectra of vibration signals showed that there is no stationary in the vibrating signal trends. In the spectra of signals there are frequencies and harmonics corresponding to the frequencies of the separator, the inner casing and the outer casing, the frequency of the rolling bodies, the negotiable frequency, the scapular and tooth frequencies and their harmonics. The signal spectra do not have obvious anomalous zones or modes. The spectra show a slight increase in amplitudes in the frequency range from 4 to 7 kHz with a pitch between harmonics close to one of the characteristic frequencies of the bearing defect. For engines in the pump unit is characterized by the presence of high amplitudes at frequencies multiple of the frequency of the blades (6 and 12 rotation frequency). In the vibration spectra along the Z-axis, there are components with a frequency of 49.992 Hz.
A deeper analysis of the operating modes of electric motors is performed using phase diagrams «vibration acceleration – vibration velocity» and «mean square deviation of vibration intensity – the standard deviation of the acceleration». The analysis of the diagrams «vibration acceleration – vibration velocity» made it possible to establish the qualitative boundaries of the zones of vibration levels of the considered electric motors with a low, acceptable, most frequent; increased and dangerous level of vibration.
The construction of phase diagrams gives an integral evaluation of the stability of the operating modes of electric motors and can be considered as an essential addition to the classical analysis of the results of vibrodiagnostics. On this basis, it is possible to pre-rank the quality of the electric motors.

References:
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