Troubleshooting VFDs

 In Documentary

Variable Frequency Drives (VFDs) are being used in an increasing number of applications to improve efficiency, protect motors and save on energy consumption costs. With additional use of VFDs, we have observed more requests for how to specify a VFD for an application and how to troubleshoot the VFD when a system isn’t operating correctly. 

VFDs are often integral pieces of equipment which can cause an entire plant or piece of equipment to shut down if they fail.  We wanted to provide a list of easy tips to troubleshoot your VFD and offer our team as a potential resource if you need additional help – info@elitecontrols.us.

Step #1: Safety

Safety is always our number one priority for our customers and employees. Life-threatening voltage levels are present in the VFD even after the power supply is removed.  Please contact a professional if you don’t feel comfortable and ensure you perform lockout/tagout procedures before beginning any troubleshooting.

Step #2: Display

Usually the VFD will tell you where to look for an issue.  Looking at the display (or keypad) for an error code and referencing the manufacturer’s programming manual is most often the best first place to look.  An example on the Danfoss VLT Micro Drive  – towards the end of the manual, troubleshooting guides based on alarm codes are detailed for the user and an explanation of the difference between a warning and alarm is given below.

  “A warning or an alarm is signaled by the relevant LED on the front of the frequency converter and indicated by a code on the display. A warning remains active until its cause is no longer present. Under certain circumstances operation of the motor may still be continued. Warning messages may be critical but are not necessarily so. In the event of an alarm, the frequency converter will have tripped. Alarms must be reset to restart operation once their cause has been rectified.”

A detailed table helps users to understand whether to check for phase loss on the supply side, DC overvoltage, DC undervoltage, inverter overload, motor heat, over current, short circuit, etc.

Step #3: Connections

If the fault codes don’t help to track down the problem, the next place you might check are connections for power supply to the VFD.  Sometimes a visual check is enough to see a loose connection, or you can check for voltage drop if you’re still connected to power or resistance if powered down.

Step #4: Temperature

You can also check connections by temperature (using a probe or IR-thermometer) to tell if they’re loose. Its important to examine the drive and the motor (this you can sometimes just smell if it’s hot) because improper motor insulation can cause overheating and a short that will trip the system.

Step #5: System Evaluation

Often, frequent problems with VFDs can be related to the overall specification of the system and not the VFD itself.  As outlined by EC&M, checking the following areas can also lead you to a solution:

  • Breaker – are they sized properly from the drive back to power service
  • Current to the motor
  • Voltage notching
  • Inductive noise in signal, control, or power wiring
  • Damaged signal, control, or power wiring
  • Current through the controller during sudden load changes, or during speed ramps

Elite Controls, Inc. has a team with over 50 years of engineering expertise in control systems, we are happy to help diagnose problems and specify the right VFD for your system. Contact us at info@elitecontrols.us for further assistance.