Cause : Fault message from thyristor check function (active in operating state o3)
This fault message can be activated only if the thyristor check is activated via parameter P830.
If “Thyristor defective” or “Thyristor unable to block” is signaled, then the relevant thyristor module must be replaced.

Possible causes for irreparable damage to thyristors:

♦ Interruption in snubber circuit

♦ Current controller and precontrol are not optimized (excessive current peaks)

♦ Inadequate cooling (e.g. fan is not operating, ambient temperature is too high, fan is rotating in wrong direction (incorrect phase sequence), inadequate air supply, heatsink is very dirty)

♦ Excessive voltage peaks in incoming supply system

♦ External short circuit or fault to ground (check armature circuit) If “Thyristor unable to block” is signaled, the cause can generally be attributed to a firing circuit fault, rather than to a defective
thyristor.

Possible causes:

♦ Firing pulse cable to relevant thyristor is interrupted

♦ Ribbon cable X101 or X102 is incorrectly inserted or interrupted

♦ Defective electronics or gating board

♦ Internal interruption in gating cable in thyristor module