5 Steps To Begin Variable Frequency Drive Troubleshooting
OH NO! Your Variable Frequency Drive (VFD) is not working! What do you do?!
Here are 5 steps to begin troubleshooting.
#1 Inspect for physical damage
Look to see if there are signs that the magic smoke hasn’t been released. Inspect the device and its surrounding area to ensure there is no sign of soot that points to an electrical device failure. If there are signs that something has combusted, shut off incoming power and alert the powers to be that a replacement must be installed. For help with this check out this article on what to consider with a VFD startup.
#2 Verify incoming power
There is a power source feeding the VFD and now is the time to verify that nothing has interrupted this supply. It is important to check items such as fuses, circuit breakers and disconnects upstream to make sure they are intact and ready to operate. Appropriate meters should be utilized and never test without proper training and adhering to your company safety policies. For additional resources on testing electrical distribution equipment the resources found here may be helpful.
#3 Validate fault codes
Fault codes are a great way to learn what the drive experienced and caused issues. While they vary from manufacturer to manufacturer there are some core faults that can point to the underlying issues you are experiencing. The primary faults are:
- Overvoltage – DC bus measures a voltage higher than it should be
- Overcurrent – motor current exceeds acceptable FLA from the motor nameplate
- Overtemperature – drive/motor is overheating
- Motor Overload – motor runs at higher levels than designed for extended periods of time
- Ground Fault – something causing the VFD to conduct to ground
- Undervoltage – adequate voltage to charge the DC bus is not being supplied
Faults can provide great insight into what occurred and corrective actions to take moving forward. Many VFD’s will have a fault history and that is a great place to begin the process of reverse engineering what occurred.
#4 Check Run and Frequency Reference Signals
Without the presence of a run command the VFD will not operate. While this seems simple enough there are plenty of technicians that spent too long going down the wrong path to only find out later the VFD was not getting the proper run command. Along with that input there should be a frequency reference signal to instruct the VFD what output it should provide. A great troubleshooting tip is to switch the drive from remote to local and try to manually run the drive. Note by doing this the motor could run so you must pay close attention to what load is being driven to ensure safe operations. If this causes the VFD to operate, you can isolate your further troubleshooting to these sources as you have identified the root issue.
#5 Ensure stop circuits are satisfied
All safety circuits must be closed to ensure the control circuit is satisfied. This includes items such as safe torque off sensors, thermal sensors, and other safety switches that keep the drive from running to increase safety overall. If one of these items has been opened the circuit is performing as designed and that will prohibit the VFD from operating.
There you have it – 5 steps to take when your VFD is not operating. While these only scratch the surface of VFD troubleshooting we have experts and resources available to support further. Connect with the EECO VFD team and let us help you solve your complex applications.
For further support on this great technology check out the following resources: