Preventive maintenance on your variable frequency drives isn’t complicated, but can save you a lot of downtime and grief.
EMA has been in business now for almost 23 years, and we do field service on VFD s every day. Most of the time, when we get a call from an industrial facility, it’s an emergency situation. Many of those calls could have been averted with a simple PM program.
EMA does preventive maintenance on everything from simple HVAC fan and pump drives, to complex coordinated drive systems. The PM s are performed on both small and large horsepower VFDs, including medium voltage VFDs.
Here are 5 things to watch for.
- Contaminants: Many VFD failures are heat related. A natural byproduct of switching components (like those found in VFDs), is heat and the drive’s ability to dissipate that heat can be restricted by contaminants such as dust, oil, or debris. For every 10 degrees C rise in temperature, the life of electronic components is reduced by half. A PM program should involve cleaning the drive, especially the heat sink and checking for proper operation of all cooling fans.
- Loose Connections: Loose connections are another very common reason for drive failures. As current “jumps” between 2 loose connections, a small arc can occur. Over time, the oxide build up in that gap will essentially terminate the connection. Not to mention, that a loose connection is in essence a high resistance connection. Run current through a resistance, and you get heat. A PM program should involve checking all connections and tightening loose ones.
- The “eye” check: One of the most commonly used troubleshooting techniques (don’t tell my boss I’m letting you in on these industry secrets) is a simple visual inspection. A large number of problems are found by simply looking for discolored or bulged components on printed circuit boards. Electrolytic capacitors, another common failure item, tend to bulge and leak before they completely go bad; this is usually fairly obvious to see, as are burnt resistors and ICs. A PM program should include visually inspecting all printed circuit boards.
- Get ahead of future problems by taking measurements: By taking simple readings such as input/output voltage, DC Buss voltage, DC Buss ripple, control power supply voltage, and input/output current, one can see indications of future problems. The general rule on the input and output current is balance. For example: If you read 40 amps on the T1 motor lead, you want to have around 40 amps on the T2 and T3 motor leads as well. If you’ve got a phase much higher or lower than the others, you have a potential problem on your hands. A PM program should include taking live measurements. WARNING: If you are not familiar or comfortable with high voltage electrical equipment, you should have a trained technician, such as one from EMA, take these readings.
- Check for proper operation: An often overlooked benefit to PM is having someone make sure the drive is in fact working as it should. A common finding is changed parameters which affect drive operation. In cases like this, there isn’t anything actually wrong with the VFD, it just isn’t running as it should. A PM program should include an operational check of the drive by someone who understands the application.
*Bonus Tip* (your reward for reading this far down). Preventive Maintenance allows you to familiarize yourself with the VFD. PMs are generally performed during a low-stress, scheduled, time, so use this time to familiarize yourself with the VFD and expand your knowledge. No one wants to learn how things work when the machine is down and your boss is looking over your shoulder (that’s when you call EMA). A PM is a perfect time to do this!
As always, EMA has the best technicians and engineers in the business. Our PM program is much more comprehensive than what is mentioned above. To get information on our Preventive maintenance, click the SERVICES tab at the top of this page. To schedule PM or repair service, click the contact icon on the top right.
Remember for long VFD life; keep them clean, keep them cool, and keep our competition away from them!
Trey Mayfield, EMA