Air resonance Group diagnose the fault
..........................................................................................................................................................................................................................

Abstract: The oxygen compressor vibration fault diagnosis of the practice, come resonance unit of the general characteristics of the fault. These conclusions, the diagnosis of rotating equipment failures resonance has an important reference.
Key words: air compressor group; resonance; fault diagnosis
Key words: TH45, China: B
 
     Our 16,000 m3 oxygen unit is the introduction of the last century France 60's production of second-hand equipment, put into operation in 1992. In addition to the air compressor group which was put into test when the failure occurred vibration, stability is still running. In November 2003, the unit of the main rotor because of a burning bag, the replacement of the main motor. Conjoined at the test, the emergence of a strong vibration motor can not run. To this end, we had a crew of the vibration monitoring and diagnosis. This article describes the unit fault diagnosis and management of the practice and experience.
     First, unit structure and layout of the measuring point
     1. Unit structure and parameters
     Units of the structure shown in Figure 1. Motor-driven gear through the four H-type air compressor. Synchronous motor for electric power 7650kw, speed 1500r/min. Compressor air flow 93000m3 / h, I, Ⅱ-class speed 4203r/min, dish, IV-class speed 617lr/min.
     2. Measuring points
     Points in the bearing, as shown in Figure 1. Level. And the vertical axis were recorded as H, V, A.
     Second, the failure analysis
     1. Failure to describe the phenomenon
     Vibration monitoring found that the vibration motor has the following features.
    (1) Electrical monomers test, vibration in good condition and the measuring point ①, ② value of the vibration is not, in the following 20μm. But when the compressor and motor-linked test, the vibration of the compressor in good condition, bearing vibration in the Department about 20μm, and the vibration motor is very intense. The December 13, 2003, the table Measured using hand-held joint-time test points ① the H, V and A vibration to the value of 66μm, 190μm and 77μm.
     (2) If in a short time idling Couplings torn off and the motor, the motor can not return to single test at the time of normal. For example, the measuring point ① V of the speed of vibration in the value of the motor when less than a single test Imm / s, conjoined by the test after motor idling, to 14.lmm / s.
     (3) electrical measurements on the same point in three directions on the obvious difference between the value of the vibration to the vertical direction for the largest.
     2. Fault diagnosis
    (1) of the vibration motor fault diagnosis, some began to take a detour. On the first motor vibration spectrum analysis found that the frequency spectrum in a very prominent component, that is, electric power frequency dominant component. It is common sense that at this time should first consider the existence of imbalance in the rotor failure. Speed of 1500r/min for the synchronous motor, should also be given to electrical factors. However, the motor points of the two horizontal vibration of the small value is inconsistent with the general characteristics of the unbalanced fault. In addition, the electrical power in the moments immediately vibration significantly reduce the value of that vibration and electrical factors. Based on the above analysis, to determine the vibration motor failure by the electrical aspects of the factors. After electric motor to re-examine and adjust the parameters, the vibration fault still exists, to prove the above conclusions of the diagnosis is wrong.
     From then on the motor speed up analysis of the curve that caused the miscarriage of justice is mainly due to the electrical power after the vibration of its value immediately as a significant reduction in electric power brought about by the effects. In fact, due to the electrical work and speed up the speed curve on the emergence of vibration when the peak is too close to the speed, power, motor speed quickly away from the Office of the peak speed of vibration, the vibration of its value immediately in order to significantly reduce , Shown in Figure 2. If you do not use specialized equipment, people feel alone, vulnerable to this phenomenon as the electric power effect, resulting in a wrong diagnosis conclusion.

     (2) in resetting the magnetic center to replace the motor bearings, bearing motors to adjust and the tight space, full-speed re-balancing rotor, and so on, as well as on the coupling bolts by the weight of symmetry, such as the installation of a series of checks and adjustments, Vibration motor failure can not be ruled out. Concluded that the electrical fault may be the basis of the vibration problems caused by the resonance unit.
     The vibration motor is not only intense but also very unstable amplitude, time was rapidly increasing flared. For example, in 2min time monitoring, measuring point ① V vibration displacement from the beginning of 150μm, will soon increase to 300μm, and then reached 600μm. If mechanical or electrical aspects of the reasons, regardless of how severe vibration, in a relatively short time, the value of the vibration of the growth will not so quickly. Only in the event of self-excited vibration, such as film or forced oscillation caused by vibration resonance, the vibration of its value will grow so quickly.
     In the test, the value of the vibration motor oil temperature changes are not sensitive to vibration there is no indication that the failure by the oscillation arising from the oil film bearings.
     However, on the basis of the problems caused by the resonance unit to the conclusion that in a long time there is no consensus, especially as a basis for reinforcement after the vibration motor still has not been eliminated (later proved, mainly because of measures to deal does not go far enough), It also increases the number of people on the conclusion of the suspected diagnosis.
    (3) on single-motor, the natural frequency of the electrical system and ƒ1 support stiffness k1;, the quality of the rotor m1; about. When the compressor and motor on-line, should motor, coupling, and the compressor-based system as a whole to look at. In this way, the entire unit of the system natural frequency has changed. Therefore, it is easy to understand why, when normal electrical test monomer, and the compressor and conjoined test when a strong resonance.
     These can also be judged on the basis of the reinforcement from the deal after surveying the results to be confirmed. The unit basis for a framework of the overall structure of several "day" shaped beams and the column constituted 6. Compressors and motors were installed on both ends of the foundation. Electrical failure in dealing with the vibration, on the basis of a total of two reinforcement. For the first time, on the side of the electric motor and the vertical axis of the two beam reinforcement, and compressor side of the two beams on the crack filling made of plastic and carbon fiber surface adhesion to deal with. After the deal, electrical test monomer, the basis of its vibration than not to deal with the former better, ① H, ① V, ① A were 4μm, 3μm, 6μm. Conjoined test, although the vibration motor is still severe, but the vibration characteristics than the pre-consolidation has improved. From the motor or
Speed curve can be seen, 1200r/min to 1470r/min range of the steep slowdown in some form. In addition, three of the original motor direction from the vertical vibration of the more prominent becomes more prominent axial. These phenomena show that the foundation reinforcement, the vibration characteristics of the system has changed. As a result, on the basis of the processing in the right direction. After the second reinforcement of the motor speed or curve further shows that the vibration characteristics of the unit has been significantly improved.
     Third, the failure to deal with
     Based on the reinforcement of the second compressor is measurement on the basis of the cracks between the columns and beams with concrete poured into one, at the same time on the motor side of the column between the use of angle steel reinforcement. Conjoined test, the motor bearing before and after the Department of vibration are reduced to below 60μm, the failure to eliminate the vibration motor, the unit returned to normal operation.
     IV, Conclusion
Through the oxygen of the air compressor vibration fault diagnosis of practice can be summed up by the unit resonance with the general characteristics: (1) vibration frequency spectrum on the outside frequency compulsory component is very prominent; (2) occurs Unit resonance, Their unstable Vibration amplitude; (3) When the unit resonance, its vibration is usually a very strong showing of a one-way.