How To Troubleshoot Problems With A VFD

Variable frequency drives (VFDs) adjust the frequency and voltage of your power supply to control the speed and torque of your AC motors. This has several benefits for the industrial, manufacturing, and processing sectors.

A VFD matches the torque and speed of your electric motors to your requirements. It improves the energy use and overall efficiency of your system and even reduces noise levels during operations. But when things go wrong, you need to know how to troubleshoot problems with a VFD quickly and simply.

3 Ways To Troubleshoot VFD Problems

Excess heat, condensation, or erratic performance are usually the first signs that a VFD is not functioning properly. Never ignore these signs.

Check The VFD Fault Codes

VFD fault codes can give you a good idea of where the issue lies.

• An Overheat error code usually indicates that the drive/motor is overheating due to a high ambient temperature, or a failed component like a faulty cooling fan.

• An Overvoltage error code means that the DC bus voltage is exceeding the VFDs threshold.

• An Undervoltage error code usually indicates that the DC bus is not being supplied with high enough voltage. But it can also mean that there is an uneven current draw due to a short in the motor or degradation of internal drive components.

• Are you seeing an Overcurrent error code? This is a protective mechanism that kicks in when the current spike reaches over 250% of the VFD’s current rating. Rapid changes in load torque, electrical or even mechanical errors, may be to blame.

• A Motor Overload error code shows that the motor current has exceeded the VFD or motor parameters. A high starting current or spiking voltage may be to blame.

• A Ground Fault code indicates that electricity is being bled to the ground. The code may also say “earth leakage” and the drive may trip. This type of fault can damage the drive, so you need to get the motor and wiring insulation checked.

Check For Physical Damage

If you are uncertain of where the fault lies, physical inspection often identifies the problem very quickly. There are some common physical signs to look for such as soot build-up or signs of burning, discoloration, or cracking.  

If you see any of these signs, the components showing physical damage need to be replaced. Shut off the power and order a replacement part right away.

Check For Incoming Power Issues

If you don’t see any obvious signs of damage to the VFD, it could be a power supply issue. To rule out problems that may be interrupting the power supply, check the basic components like upstream fuses, circuit breakers, and disconnect switches. The simplest way to check them is to use a digital multimeter.

Fuses

Check the fuses with a multimeter, by touching the probes to both ends of the fuse, in continuity or resistance mode. If your multimeter does not have a continuity setting, turn the dial to the lowest number in resistance mode, measured in ohms (Ω).

An infinite ohms reading means that the fuse is blown and needs to be replaced.

Circuit Breakers

For your safety, switch off the main power or switch the circuit breaker off at the box. Remove the circuit breaker box panel and detach the circuit breaker from the rest of the electrical system. Set your multimeter to the lowest setting in resistance mode.

Touch the red probe of the multimeter to the power supply terminal and the black probe to the terminal connected to the circuit breaker panel. Any reading you get other than zero ohms shows that the circuit breaker is indeed at fault.

Disconnect Switches

You can also troubleshoot your VFD problems by testing disconnect switches with a multimeter. Turn off the power supply to the switch. When you are certain that no power is running to the switch, open the switch box and disconnect the wires. Once again, set your multimeter to continuity or resistance mode.

Touch the multimeter probes to the disconnect switch’s terminals. The multimeter should display zero ohms reading with the switch on and infinite ohms when off. If that is not the case, your disconnect switch is faulty.

Some switches can also be tested for continuity without disconnecting the power or wires. Always refer to the safety instructions for both your multimeter and disconnect switch.

Conclusion

At AEC, we know how important proper maintenance is to keep your automated processes running smoothly. A faulty VFD can cause a variety of problems that will impact your processes and cause unnecessary delays.

This is why we stock a wide range of components to keep you and your business on track. Contact us today for the best in automated control systems and standard panel parts and accessories.