I received an application for vibration diagnostics of an electric motor of type 5AN355 V4 U3 (400 kW, 1480 rpm) after a major overhaul. This electric motor works in tandem with the mains pump at the boiler house in Reutov.
Measurement of the vibration of the electric motor was carried out in order to obtain data on the vibration parameters and their further comparison with acceptable values regulated by GOST IEC 60034-14 (2018). After incoming control, it was necessary to perform laser alignment with the pump and put the unit into commercial operation.
Vibrodiagnostics was performed on 09/05/2018 by a second-level specialist in vibration analysis of machines Stanislav Antonychev, using the QUARTZ vibration analyzer, plant No. 135.
The examined electric motor type 5АН355 В4 У3 belongs to the category "A", with a height of the axis of rotation of more than 280 mm, and has a rigid mount.
According to the results of vibration diagnostics, it was found that this electric motor 5АН355 В4 У3 is not allowed to operate due to exceeding the maximum permissible vibration values, standardized by GOST IEC 60034-14 (2018).
At idle, on a warm engine, at point 1 - in the axial direction (at a reverse frequency of 25 Hz), the value of vibration velocity is fixed at the level of 18.51 mm / s (Fig. 1), which is 7 times higher than the vibration velocity level 2 allowed for this unit , 8 mm / sec.
The presence of the VFD made it possible to measure the vibration of the heated engine at different speeds. From table 2 it is seen that with increasing speed of the motor shaft increases the level of vibration on the bearing shields.
Assuming that this is possibly grazing, a dump of the vibration acceleration signal (rotation speed 1480 rpm (50 Hz)) was recorded at point 1O (Fig. 2).
Then we decided to try to balance the impeller of the engine cooling. After calculating the mass and the installation angle, we hooked a load (in the form of a clothespin) weighing 18 grams, which immediately removed the axial vibration (from 18.51 mm / s to 1.5 mm / s). But our glee did not last long, since the engine, having worked with the balancing weight for about 15 minutes, fired axial vibration at the point 1 ° (at the reverse frequency of 25 Hz) for 21 mm / sec.
After all the experiments, they decided that the engine was unsuitable. The mystery of the cause of axial vibration on a warm engine has remained unsolved to this day!
Regardless of the cause of the increased axial forces on the thrust bearings, this is a rather dangerous defect. Most rolling bearings are not designed to compensate for axial forces, and therefore in this situation they quickly fail.