Quote:
Originally Posted by Porsche-O-Phile
There are concerns about VFDs now starting to come to light that deal with eddy current creation in motor bearings and other components. This probably isn't a huge deal for a residential pool pump and the fixes are supposedly relatively straightforward (grounding rings, non-conductive bearings, things like that) but in some applications it can be a huge deal. I'm running into this now involving exhaust AHU fans serving a critical lab building.
VFDs are generally a good technology but there are quirks related to using them that aren't readily obvious or fully understood by many engineers (ask your EE if he or she has reviewed or commissioned a harmonics study for whatever facility they intend to install them in before doing so - if they look at you like you have three heads, run away). Also make sure that any pumps and motors are specifically rated as VFD compatible so you can get a warranty later if there's an issue and not end up potentially buying them twice.
Ahh, the joys of new high-tech stuff in buildings...
|
When working for a large manufacturer of centrifugal water chillers there were problems with the rotor discharging a stored electrical charge through the steel ball bearings to the bearing race on the back end of the motor on VFD machines. Eventually the bearings would degrade and start to rumble.
The fix was to remove the defective bearings at the back end and install ceramic bearing sets. Also the back bearing cover plate was re designed to allow the installation of a grounding brush on the end of the motor shaft. Was kind of crude but it worked.
Most motors that are installed for VSD/VFD are designed for the purpose. Not that it prevents all failures.