I am facing a similar type of problem in our VFD, it is giving F0027, F0026 and F0025 faults. I had changed all cards with new including CUVC, IVI and IGD cards. It worked fine for about one week. After one week the problem started again. I checked all the IGBTs all are working Ok.

Our application is for a drilling rig, Top drive.

At random if I reset the fault it starts to rotate (once in say 20 attempts) and immediately fault 0027 appears. Motor with cable is OK, I disconnected the cable and got a megger value of more than 5 Mohms.

The remaining cards we do not have changed is the cards above the IGBT

Is it ok to megger the motor with drive connected?

What may be the probable causes?

Is the humidity in the compartment any way effect the performance?

Thanking You

Sagar