Variable frequency drive users look to drive manufacturers and reps not only for quality products but expertise. If they don't find the knowledge to fix any problems they run into, they may go to another brand. But more positively, the more expertise you show, the more you build their loyalty. And if you can stave off any problems they might later run into, so much the better.
One way that drives salespeople and reps already do this is by recommending using inverter-duty motors (with Class F or H insulation) with drives. Drives protect the motor windings from turn-to-turn shorts due to the VFD output's high dV/dt. Some motors, on some drives, in some applications, will be alright with Class B insulation, but why take the chance?
The Problem of Shaft Voltage
Burnt out windings aren't the only risk that drives pose to motors. The common mode voltage of the three phases capacitively creates a potential difference between the rotor and motor frame. This so-called shaft voltage can discharge destructively through the bearings, often drastically shortening bearing life. Now, is every motor running on a VFD going to have its bearings fail prematurely? Maybe not, but why take the chance? Why not just avoid the problem altogether?
The best and easiest way to prevent this premature bearing failure is to recommend that your customers use motors with AEGIS® Shaft Grounding Rings factory-installed. AEGIS Rings discharge shaft voltage safely to ground, channeling the discharge currents around the bearings. These long-lived rings protect:
- motors from premature bearing failure
- your customers from the expense of repair/replacement and associated downtime, and
- you from customers understandably angry that their new motor failed after just a few months
Best of all, by warning customers of this problem, and solving it, you will be showing your expertise, and continuing to earn their loyalty.
Motors with AEGIS factory installed are available from ABB Motors & Mechanical, WEG Electric, Marathon, TECO, LEESON, GE, and many moreFor more on the problem of capacitively coupled bearing current and its mitigation with AEGIS rings, see our Bearing Protection Handbook. Or even better, you can request a Lunch & Learn training, worth one Professional Development Hour.
