Variable Frequency Drives (VFD) are not intended to be used as a form of circuit protection (smoke in = good; smoke out = bad). In of themselves they offer small amounts of protection for the internal components.
One protective feature is the ability to detect and interrupt ground faults.
So, what is a ground fault? A ground fault is caused when electricity is being bled to the ground from any point in the motor circuit. When this occurs the HMI of drive will usually display something such as “GF”.
Below are some causes and solutions for troubleshooting a ground fault in a VFD:
- The motor may have shorted from a voltage spike, overheated windings, aged insulation, or from an external conductive containment that is connecting the motor windings to ground. If the windings are compromised, the motor will need to be rewound or completely replaced.
- To ensure the VFD is not the root cause, completely disconnect the output leads of the drive while power is off. Apply power to the drive and give it a run command. If no fault occurs, the motor or the leads are the issue.
- If the fault remains while disconnected, then there is an internal issue with the drive, and it is time to go to the bullpen and get a replacement.
- If the insulation on the cables was compromised, current can bleed to ground if it touches a conductor.
- Wire insulation can become compromised from melting after an overcurrent event, damage during installation such as pulling cable that isn’t highly flexible causing it to break and bend, or from an external source such as animals thinking it is a snack.
- Wire insulation can be tested with a megohmmeter to see if the leads are the issue causing a ground fault.
These two areas are great places to troubleshoot and understand why your VFD experienced a ground fault. The team at EECO is here to serve you with VFD support and you can connect with us here to learn more.