F517 fault in ABB DCS880 drive indicates Armature current ripple. This means one or several thyristors may carry no current.

1. Check the values of 01.50 Current ripple and 01.51 Current ripple filtered1.
2. Check the setting of 31.46 Current ripple function and 31.47 Current ripple level.
3. Check for too high gain of current controller. See 27.29 M1 current proportional gain.
4. Check the positive/negative current feedback with an oscilloscope (6 pulses within one cycle visible?).
5. Check the thyristor gate-cathode resistance.
6. Check the thyristor gate connection.
7. Check the current transformers (T51, T52).
8. Check the condition of the mains (voltage, cabling, fuses, switchgear).