Most VFD repair can be prevented with routine maintenance. VFD repair cost and lead times can also be reduced with routine maintenance. VFD repair can be expensive and also cost manufacturers production downtime during the VFD repair process. Most manufacturers keep spare VFD units in stock to prevent production downtime whenthe VFD repair isin process.
Checkingconnections is a step many people miss or do incorrectly during the VFD repair process. Heat cycles and mechanical vibration can lead to sub-standard connections, as can standard preventative maintenancepractices. Reusing torque screws is not a good Idea, and further tightening an already tight connection can ruin the connection.Bad connections eventually lead to arcing. Arcing at the VFD input could result in nuisance over voltage faults, clearing of input fuses, or damage to protective components. Arcing at the VFD output could result in over-current faults or even damage to the power components.
Loose connections can cause erratic operation. For example, a loose START/STOP signal wire can cause uncontrollable VFD starting and stopping. A loose speed reference wire can cause the drive speed to fluctuate, resulting in scrap, machine damage, or personnel injury.
Conduct Diode and IGBT Tests
There are a number of methods to test the input and output power sections of aVFD, and this step is essential prior to applying power to the VFD unit. If for any reason there is a short on the input side or output side of the VFD, further damage can be caused to the unit if power is applied to it.
For this reason, Precision Electric uses meters to properly test the input and output power sections of the VFD prior to applying power to the actual unit. If a short is found, the unit can be disassembled and the cause of the short can be diagnosed and quoted for repair. If the repair is too costly, then a replacement is offeredto the customer.
Power Up Unit
If the input and output power sections test healthy during this step of the VFD repair process, Precision Electric will power the unit and perform amp reading and output frequency tests. Precision Electric prefers to slowly increase power voltage to the unit until the rated input voltage of the VFD is achieved.
Depending on whether or not the VFD provides a display will determine what further action(s) will be taken. If display is unavailable, dis-assembly and diagnosis of the internal power supply of the control section of the VFD is likely necessary to further evaluate cause of failure and establish costand lead time for the VFD repair.
Run A Motor
If the previous three tests have passed during the VFD repair process, then it is time to run a basic jog function of the VFD with a simple template program. Often when a VFD comes into our facility, we make sure to backup whatever program is currently stored in the VFD prior to inputting a template program and running a test procedure. This ensure we have a backup copy of the program.
The best method for backing up depends on the brand of drive, but after it has been backed up, we either reset the VFD to factory defaults through the keypad and recommission a basic start, stop and job application or closed loop if an encoder is involved. If the motor will not run, it will be necessary to checkthe output voltages and current ratings going to the motor to see if the VFD is functioning properly to rotate the motor.
At this point we have determined the cause of failure, estimated lead time and costof the VFD repair. If the VFD has tested good entirely, then further underlying issues are communicated with the customer. This is when Precision Electricwill gather application specific information from the customer to establish whether or not it may be some outside issue associated with the system including, but not limited to, PLC communications, faulty IO, bad wiring or even bad cabling. There is no single way to do this step, as it really depends on a wide variety of variables.
Send Service Tech
If the customer cannot establish failure on any other aspect of the machine and the VFD appears to test fine, then it may be necessary to send a field service technician on site to establish cause of failure. Field service technicians should betrained to troubleshoot any issue ranging from standard VFD repair, to advanced robotics, PLCs and more. Field technicians should also be trained to establish cause of failure and come up with solutions as quick as possible.
VFD repair should be taken with extreme caution. VFD repair should only be performed by technicians who have required training and experience to work with electrical equipment. Precision Electric strongly recommends to consult an expert in the field when repairing VFD equipment.Many VFD controllers have an internal DC bus that retains a charge after power has been cut to the drive, as a result, it does not mean it’s safe to work with. Technicians working with VFD repair must always take extra precautions to ensure proper safety measures are taken, or injury or even death may occur.
For VFD repair and VFD replacement quotes, contact Precision Electric.