ATV320 trips SCF3 at start, after washdown, what to check?
My Altivar ATV320 drive is tripping on SCF3 (Ground Short Circuit) right at startup. This started happening after a recent washdown of the machine. What should I check first?
An SCF3 fault on a Schneider Altivar ATV320 drive indicates a significant earth leakage current at the drive's output. This fault often occurs at start-up or while running, especially with multiple motors connected to one drive or in damp conditions. Since it happened after a washdown, insulation issues are highly probable.
Likely causes and checks
1Motor cable insulation to ground
- Points to it
- Water ingress from the washdown could have damaged or compromised the insulation of the motor cables, leading to leakage to ground. This is a common cause, especially if cables run through wet conduits.
- Check
- Lock out the machine and confirm the DC bus voltage is below 42 Vdc. Disconnect the motor cable from the drive and use a megohmmeter to test each conductor to ground.
2Motor winding insulation to ground
- Points to it
- Similar to cable insulation, the motor windings themselves could have been affected by moisture from the washdown, leading to a breakdown in insulation to ground.
- Check
- If the cable insulation tests good, disconnect the motor from the drive and megger the motor windings to ground.
3Leakage from several motors or long cables in parallel
- Points to it
- If multiple motors are connected to this single drive or if the total cable length is extensive, the cumulative capacitive leakage can trigger an SCF3 fault, especially if dampness exacerbates the issue.
- Check
- If insulation tests for both cable and motor are good, consider connecting chokes in series with the motor and reducing the switching frequency (SFR) parameter on the drive.
4Speed loop or brake settings
- Points to it
- While less likely given the washdown context, incorrect speed loop or brake adjustments can sometimes contribute to SCF3 trips, particularly on brake-controlled axes around brake release.
- Check
- Check the speed loop and brake adjustment parameters. You might also consider increasing the [Time to restart] TTR parameter.
Next check: After addressing the cause, an SCF3 fault requires a power reset of the device unless the [Extended Fault Reset] HRFC parameter is set to 'Yes', in which case it can be cleared manually with the [Fault Reset Assign] rsf parameter.
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