1.Check for physical damage
Look for signs that magic smoke has not been released. Check the unit and its surrounding area to make sure there are no signs of soot that would indicate electrical equipment failure. If there are signs that something has burned, turn off the input power and alert the electrical department that a replacement must be installed.
2.Verify Input Power
There is a power source supplying power to the VFD and it is time to verify that nothing is interrupting this power source. It is important to check items such as fuses, circuit breakers and upstream disconnects to make sure they are intact and ready to operate. Appropriate meters should be used and never test without proper training and adherence to company safety policies.
3 Verifying Fault Codes
Fault codes are a great way to understand what problems the drive is experiencing and causing. While they vary from manufacturer to manufacturer, there are a few core faults that may point to a potential problem you are experiencing. The main faults are:
- Overvoltage - voltage measured at the DC bus is higher than it should be
- Overcurrent - motor current exceeds the acceptable FLA on the motor nameplate
- Overheating - drive/motor overheating
- Motor overload - motor running at a higher level than designed for an extended period of time
- Ground fault - cause of VFD grounding
- Undervoltage - not enough voltage is supplied to charge the DC Bus
Failures can give you insight into what happened and corrective action to move forward. Many VFDs have a failure history, which is a great place to start reverse engineering what happened.
4.Checking the run and frequency reference signals
The VFD will not run without a run command. While this seems simple enough, many technicians spend too long going down the wrong path, only to realize later that the VFD was not given the correct run command. In addition to that input, there should be a frequency reference signal to indicate to the VFD what output it should be providing. A good troubleshooting tip is to switch the drive from remote to local and try to run the drive manually. Note that the motor may run doing this, so you must pay close attention to the load on the drive to ensure safe operation. If this causes the VFD to run, you can isolate further troubleshooting to these sources since you have identified the underlying problem.
5.Ensure that the stop circuit is satisfied
All safety circuits must be closed to ensure that the control circuits are satisfied. This includes items such as safety torque off sensors, thermal sensors, and other safety switches that prevent the drive from operating to improve overall safety. If one of these items is open, the circuit operates as designed, which will prohibit VFD operation.