Although variable frequency drives are gaining a lot of popularity, they are not simple devices.  These drives are full of electronics and therefore susceptible to all sorts of problems.  These problems can range from incoming power disturbances to environmental hazards.  They have an important function and offer huge energy savings.  In mechanical applications they allow fine adjustments that wouldn’t be possible by other methods.  To keep motors running it is important to follow certain procedures, and avoid many errors.  The following is a list of these procedures:

1) Start with baseline readings of the motor by using a multimeter. Measure the starting and running amperage, the running voltage and the leg-to-leg balance.  It is also a good idea to connect a thermocouple to the clamp meter to compare results.

2) Make other measurements periodically.  Take additional amperage, resistance and insulation resistance reading, comparing them to previous readings.  If the measurements deviate by more than 5-10%, start looking for bad electrical connections or loose fitting mechanical connections.

3) Check the protection.  Look at the protection systems to see if the fusing is correct, and if the overload contacters are set too high or too low.  Check to see if the fuses are rated properly and if they blow repeatedly.

4) Don’t change parts instead of troubleshooting the actual problem.  Do not just change out parts until the problem goes away for that technique is extremely costly, and makes it much harder to find the original problem.

5) Check the line at the motor, not just the panel on the wall.  The problem may lie in the wiring, not the motor.

6) Make sure it is the right motor.  At times, motors can be put into applications they were not designed for.

7) Check for power problems.  After a power issue, it is very important to measure the power to see if the problem has been corrected.

Troubleshooting problems with VDFs can be complicated and time consuming, and it is important to follow steps to identify the root problem.