September 28, 2017
One Resolution to Motor Resonance
By Tim Sorensen
A customer was experiencing high levels of vibration on one of the HVAC motors. The cause for these high vibration levels was determined to be resonance.
Resonance of this motor was seen in the vibration spectral data and was confirmed onsite with a bump test. This motor was not VFD driven and therefore the machine speed could not be varied to avoid this resonance. During testing, an attempt to stiffen the machine to eliminate resonant amplification was made using a 2×4 as a stiffener. Unfortunately, the 2×4 could not be positioned to provide adequate stiffening.
The following pictures show stiffening that was fabricated and installed by the onsite maintenance staff.
Shown below are the spectral comparisons for the before (blue) and after (red) correction vibration data. Due to the scaling and the significant reduction in vibration achieved, the corrected vibration amplitude at operational speed is barely visible.
In conclusion: The issue with high vibration was found with vibration analysis and corrected with ingenuity.