Investigations Into the Causes of High Vibrations in Case of a Circulating Water Pump Motor
A two pole circulating water pump motor vibrations under coupled run were extremely high. Normally, the
problems with such motors are that of dynamic unbalance, resonance, misalignment or poor foundation. But the motor under
study was found to be free from all these problems. The motor has been performing well for over 800 hours but was lying
idle for few weeks prior to taking this run. The solo run of motor exhibited comparatively low vibrations but multiple
frequencies of rotational speed were observed. Thus thorough investigations were made to establish the cause of this typical
behavior. Phase measurement technique was applied and rotor bent was ruled out. The problem was ultimately traced to poor
bearing condition, which was then improved. However after coupling with the cooling pump again, vibrations were
increased. This was controlled by in situ balancing and the problem was resolved. This paper presents the description of the
entire diagnosis process and test results obtained at each stage of analysis with major findings. The analysis can be used for
diagnosis of the causes responsible for the vibration problems of any large motor.
Key Words- Spectrum, phase measurement technique, in-situ balancing, frequency components, coupling, amplitude.