What are the probable causes of SCF3 (Short-Circuit to Ground) fault in Altivar 71 drive.

1. SCF3: Short-Circuit to ground detects a short circuit current to the ground at the start-up or during the running. It is fast hardware detection based on measuring of current imbalance. The good way for suppress SCF3:---
- Test and check the insulation between phase and ground of the cable
- Test and check the insulation between phase and ground of the cable of the motor.
- Check the insulation of Motor
- Reduce the switching frequency.
- Use Motor choke depending on the motor cable length.

2. One of the root cause for SCF3 is that the mains voltage is unbalanced. For good working of VSD, the limit of voltage unbalance is +/-3%. Please check and if this is the case, then use Line Choke.

3. It is also very important to check if the ground connection is good or change since that the drive was installed.

4. If after doing above said, there is always some SCF fault, it could be necessary to decrease SPG and increase SIT.
And:
- Do factory setting of motor control parameter.
- Enter all motor parameter voltage/current/speed.
- Do the auto tuning with the motor at cold state.

Released for:Schneider Electric India