As you know, the benefits of using a variable frequency drives (VFD) are great and many. However, like all machines, they can be “moments” where you stand there, staring at it, pulling your hair out as you’re wondering what the heck is happening.
The dark side of AC drives, as listed below, is by no means a comprehensive collection of symptoms and solutions for an issue with your drive. The goal of this list is to present you with several possible issues that are the direct result of using a VFD. Should your drive “walk” down one of these paths, contact us and let one of our outstanding field service technicians troubleshoot and remedy your electronic malady.
Issues
Harmonics & EMI/RFI
Symptoms
Harmonics (Low Frequency Noise)
- Product Failure
- Can be intermittent
- Overheating Distribution Transformer
- Circuit Breaker Tripping
- Motors Burning Out
- Power Factor Capacitor Bank(?) Failure
EMI/RFI
- Static on AM radio band
- Directly effects sensitive equipment, e.g. inadvertent
security alarm activation - Radiated Issue and Conduction
Band-Aid Solutions
Harmonics
- Increase load impedance
- Install line reactors
- Harmonic Traps
- Active Filters
- Drives
EMI/RFI
- EMC filters
- EMI/RFI filters
- Drives
Output Reflective Wave (DV/DT)
Symptoms
- Identifiable Motor failure (e.g. motor failure in first turn)
- Occurs only with 380 volts and higher
- Does NOT occur in 208/230/240 volt systems
Band-Aid Solution
- Change the distance between drive and motor to a distance of approximately 50 to 350 feet
Bearing Currents
Symptoms
- Common-mode voltage possibly creates current to the bearings
leading to motor failure
Band-Aid Solution
- Proper grounding
- Common-mode filters
- DV/DT filters
- Shaft Grounding Brushes
- Insulated Bearings
Symptoms
- Drive shuts down on over-current or ground fault
- Band-Aid Solution
- Move the drive closer to the motor, within 600 feet
- Oversize Drive
