The induction motor is the most generally used industrial electric-drive. Detecting the vibration problems that occur in induction-motors has an added complexity due to the rotating magnetic-fields in the machine.
Vibration Spectrum Analysis for Motors & Generators is perhaps the most practical test for rotating machines for identifying mechanical and electrical problems. Vibration analysis can monitor many abnormalities, including wear, imbalance, misalignment, mechanical looseness, bearing damage, structural resonance, fatigue, etc.
How is it Analyzed?
Vibration Spectrum Analysis for Motors and Generators is rarely based on a single vibration spectrum. In most predictive and preventive maintenance programs, vibration spectra are acquired periodically and stored in a database. The data is then influenced by examining for changes in levels at the problem of forcing frequencies.
The influenced data must be acquired simultaneously, in the same orientation, under the same operating conditions, and with the same analyzer settings. Every time the analysis includes frequency range, window type, number of spectral averages, number of spectral lines, etc. Therefore, the transducer- mounting pads are permanently mounted on the machine.
Instruments to detect vibrations:
Three types of vibration transducers are:
1. Shaft Vibration probes with proximeters
2. Velocity pickups
The most familiar transducer is typically an accelerometer because of its widest bandwidth. It is necessary to securely mount the accelerometer or velocity transducer as close as possible to the bearings. For a sizeable high-speed machine with hydrodynamic bearings, the use of non-contacting shaft vibration probes is suggested for vibration analysis.
Some of the mechanical issues detected by vibration spectra are imbalance, misalignment, bent shaft, looseness, and bearing problems. Identification of a mechanical or electrical problem depends upon the frequency ranges and the frequency relationship between running speed, electrical vibration, and other machine’s internal or driven-equipment components.