General Troubleshooting Of VFD Problems03/14/2019They are referred to by a myriad of names – Variable Frequency Drive, VFD, AC Drive, Inverter, AC Motor Controller, even a few more “colorful” terms have been heard coming from frustrated maintenance personnel when working on them, but we’ll save those for a MUCH later time. No matter what they’re called, the ability to quickly isolate a problem on a VFD (term we’ll stick with for this conversation) is critical for today’s maintenance personnel. Here at PES, we understand that need, which is why we post helpful blogs like this one that can be used as a reference tool when troubleshooting VFD problems. Below is a list of common problems that can be found and checks / possible solutions for them. *Caution – Dangerous voltages exist when working with VFDs, even after the power has been removed (due to large capacitors in the bus circuit) – only qualified personnel should perform work in electrical panels or on VFD equipment. Be sure to follow all lockout/tagout procedures and other safety requirements per your local codes. *Allow at least 5 minutes after power has been removed before working on it to ensure the bus circuit has discharged. Click here to see our blog on this subject *Most VFDs in use today have a display for ease in troubleshooting and entering parameters. · Visual inspection (power should be off for this) Visually inspect the VFD – make sure all wires are terminated properly and look for any obvious problems such as: Burnt areas on drive or connections / wires Cooling fans (if applicable) or heatsinks clogged with lint or other debris Check the motor for: Burnt wiring or a burnt smell coming from the motor (*Removal of wiring cover plate is helpful for this) Physical damage of shaft or coupling / belt. General problems (*Not drive fault conditions) No display If there is no display on the drive, check the incoming line voltage for the rated input voltage at the drive. For units with three phase incoming power, make sure to check all three phases. With the power removed (*allow enough time for the DC buss to discharge), remove all wires except the incoming line voltage and ground (i.e. motor, all inputs & outputs to the drive) and try to power up the drive again to see if something connected to the drive could be the problem *Be sure to label all wires so they will be reconnected to the proper terminals Try to power up the VFD again with these connections removed If still no display, suspect a defective VFD Blown line fuse(s) * DO NOT replace line fuses and re-apply power without first checking drive for possible shorts. If the drive is defective and caused the fuses to blow, replacing fuses and re-applying power may cause catastrophic damage to the drive and possibly other nearby components *Click here to see our blog on testing IGBTs of a drive linked here (related to the Yaskawa A1000 series drive “Testing IGBTs on the Yaskawa A1000 Drive” If the drive has external braking components (braking resistor or braking unit), check this for possible problems After it has been determined there are no obvious problems in the drive’s power section or external braking components, replace the fuse(s) and re-apply power to the drive If the fuse(s) blow again, suspect a defective VFD Will not start If the drive display lights up, but will not start, there can be several reasons *Make sure the drive is not in a fault condition – if it is, resolve that fault condition (see below) Check for the proper type of start input being sent to the drive, either via discrete inputs or communications from other equipment *Loose wires / terminations are a common problem VFD starts but will not run Often the drive is receiving its enable / start signal but no speed signal Check to be sure the speed reference signal is getting to the drive (for how it is configured, either via I/O terminals or commutations) Drive Faults *Refer to the manual for your specific model of drive for more detailed fault information **NOTE: It is VERY important to keep manuals for ALL VFD equipment on hand for reference when problems arise. If you do not have the proper manual, it can often be found and downloaded from the Internet. Overcurrent Fault This is an indication that the drive has sensed too much current in its output Excessive load from motor Faulty motor, motor cables or connections Insufficient acceleration time (*more likely in new applications / installations or if parameter changes have recently been made) Load problem on motor (gearbox, coupling, motor in bind) Overvoltage fault The drive has sensed an overvoltage condition in its DC bus Braking circuit problem, either internal or external (wiring, braking unit, internal or external braking resistor problem) Deceleration setting of the drive is too short (parameter) Under voltage fault The drive has sensed the line voltage or its power supply voltage is too low Check incoming line voltage to be within rated specifications for the drive If three phase incoming power, check voltage on all three phases Possible that drive power supply is being loaded down by something connected to drive I/O *With power off, remove all I/O connections from drive, then apply power again to see if this is the case Drive over temperature fault Typically this relates to the heatsink of the drive being over temperature Check heatsink and fans to be sure they are clear of debris Check to see that cooling fans are running *Note: some drives only run cooling fans when motor is running or above a threshold temperature Motor over temperature fault The connected motor’s motor thermals are not being sensed by the drive Check the motor’s temperature for excessive heat Make sure motor thermals are terminated properly at the drive Ground fault Check wiring going from VFD to motor for possible nicks or bare wires touching ground Check motor for possible ground leakage (*disconnect motor from VFD before checking with insulation tester or megohmmeter) Motor overload fault *VFD may run briefly before this fault is indicated, as it usually is caused by excessive current over a period of time Check motor and connected load for possible problems Make sure VFD is properly sized and configured (motor parameters) for motor it is running External fault This fault typically refers to an external connection to drive that it is monitoring Check external circuits that are connected to the external fault inputs of the VFD If it is suspected that your VFD is defective, we are here to help! Give us a call at 800-732-4695 and let us know the problem you are having. We have been repairing VFDs and other industrial equipment since 1985, so we have the experience to help get your equipment back into production quickly. Back To Blog
General Troubleshooting Of VFD Problems03/14/2019They are referred to by a myriad of names – Variable Frequency Drive, VFD, AC Drive, Inverter, AC Motor Controller, even a few more “colorful” terms have been heard coming from frustrated maintenance personnel when working on them, but we’ll save those for a MUCH later time. No matter what they’re called, the ability to quickly isolate a problem on a VFD (term we’ll stick with for this conversation) is critical for today’s maintenance personnel. Here at PES, we understand that need, which is why we post helpful blogs like this one that can be used as a reference tool when troubleshooting VFD problems. Below is a list of common problems that can be found and checks / possible solutions for them. *Caution – Dangerous voltages exist when working with VFDs, even after the power has been removed (due to large capacitors in the bus circuit) – only qualified personnel should perform work in electrical panels or on VFD equipment. Be sure to follow all lockout/tagout procedures and other safety requirements per your local codes. *Allow at least 5 minutes after power has been removed before working on it to ensure the bus circuit has discharged. Click here to see our blog on this subject *Most VFDs in use today have a display for ease in troubleshooting and entering parameters. · Visual inspection (power should be off for this) Visually inspect the VFD – make sure all wires are terminated properly and look for any obvious problems such as: Burnt areas on drive or connections / wires Cooling fans (if applicable) or heatsinks clogged with lint or other debris Check the motor for: Burnt wiring or a burnt smell coming from the motor (*Removal of wiring cover plate is helpful for this) Physical damage of shaft or coupling / belt. General problems (*Not drive fault conditions) No display If there is no display on the drive, check the incoming line voltage for the rated input voltage at the drive. For units with three phase incoming power, make sure to check all three phases. With the power removed (*allow enough time for the DC buss to discharge), remove all wires except the incoming line voltage and ground (i.e. motor, all inputs & outputs to the drive) and try to power up the drive again to see if something connected to the drive could be the problem *Be sure to label all wires so they will be reconnected to the proper terminals Try to power up the VFD again with these connections removed If still no display, suspect a defective VFD Blown line fuse(s) * DO NOT replace line fuses and re-apply power without first checking drive for possible shorts. If the drive is defective and caused the fuses to blow, replacing fuses and re-applying power may cause catastrophic damage to the drive and possibly other nearby components *Click here to see our blog on testing IGBTs of a drive linked here (related to the Yaskawa A1000 series drive “Testing IGBTs on the Yaskawa A1000 Drive” If the drive has external braking components (braking resistor or braking unit), check this for possible problems After it has been determined there are no obvious problems in the drive’s power section or external braking components, replace the fuse(s) and re-apply power to the drive If the fuse(s) blow again, suspect a defective VFD Will not start If the drive display lights up, but will not start, there can be several reasons *Make sure the drive is not in a fault condition – if it is, resolve that fault condition (see below) Check for the proper type of start input being sent to the drive, either via discrete inputs or communications from other equipment *Loose wires / terminations are a common problem VFD starts but will not run Often the drive is receiving its enable / start signal but no speed signal Check to be sure the speed reference signal is getting to the drive (for how it is configured, either via I/O terminals or commutations) Drive Faults *Refer to the manual for your specific model of drive for more detailed fault information **NOTE: It is VERY important to keep manuals for ALL VFD equipment on hand for reference when problems arise. If you do not have the proper manual, it can often be found and downloaded from the Internet. Overcurrent Fault This is an indication that the drive has sensed too much current in its output Excessive load from motor Faulty motor, motor cables or connections Insufficient acceleration time (*more likely in new applications / installations or if parameter changes have recently been made) Load problem on motor (gearbox, coupling, motor in bind) Overvoltage fault The drive has sensed an overvoltage condition in its DC bus Braking circuit problem, either internal or external (wiring, braking unit, internal or external braking resistor problem) Deceleration setting of the drive is too short (parameter) Under voltage fault The drive has sensed the line voltage or its power supply voltage is too low Check incoming line voltage to be within rated specifications for the drive If three phase incoming power, check voltage on all three phases Possible that drive power supply is being loaded down by something connected to drive I/O *With power off, remove all I/O connections from drive, then apply power again to see if this is the case Drive over temperature fault Typically this relates to the heatsink of the drive being over temperature Check heatsink and fans to be sure they are clear of debris Check to see that cooling fans are running *Note: some drives only run cooling fans when motor is running or above a threshold temperature Motor over temperature fault The connected motor’s motor thermals are not being sensed by the drive Check the motor’s temperature for excessive heat Make sure motor thermals are terminated properly at the drive Ground fault Check wiring going from VFD to motor for possible nicks or bare wires touching ground Check motor for possible ground leakage (*disconnect motor from VFD before checking with insulation tester or megohmmeter) Motor overload fault *VFD may run briefly before this fault is indicated, as it usually is caused by excessive current over a period of time Check motor and connected load for possible problems Make sure VFD is properly sized and configured (motor parameters) for motor it is running External fault This fault typically refers to an external connection to drive that it is monitoring Check external circuits that are connected to the external fault inputs of the VFD If it is suspected that your VFD is defective, we are here to help! Give us a call at 800-732-4695 and let us know the problem you are having. We have been repairing VFDs and other industrial equipment since 1985, so we have the experience to help get your equipment back into production quickly.