17
Fault Tracing Thyristors
3ADW000488R0101 DCS880 Service manual e a
Additionally for service and preventive maintenance
Following additional tools are mandatory for cleaning:
− An ESD safe blower/ESD vacuum cleaner (ABB
Service Finland code 0006ESD/MUNTZ 555-
ESD-S-E).
How to detect a faulty thyristor
Thyristor problems can be noticed differently:
A fuse is blown
This is an indication that a strong overcurrent has happened due to one of the following reasons:
− An internal short circuit between the phases (line side/AC-side) because of a defective thyristor (short circuit
inside a thyristor from anode to cathode).
− An internal short circuit between the phases (line side/AC-side) because of circulating current in a 4-Q
converter (malfunction of the control electronics, no thyristor defective).
− An external short circuit at the DC terminals of the converter without sufficient impedance.
− A commutation fault during generating (active braking with high current, high EMF and with low AC voltage)
of a 4-Q converter.
Note:
− In case of parallel fuses: If one of the parallel fuses is blown, all parallel fuses have to be changed. The
‘undamaged’ fuses might be ‘half-blown’ and will blow with the next high current.
− In case of serial fuses (e.g. DC-fuses): If one of the serial fuses is blown, all serial fuses have to be
changed. The ‘undamaged’ fuses might be ‘half-blown’ and will blow with the next high current.
DC-current pulses measured using an oscilloscope
Connect an oscilloscope at the fixed AO named IACT (XAO:4/5 on the SDCS-CON-H01) and check for the
proper amount of current pulses:
There should be six current pulses in positive direction.
In case of a 4-Q converter also the six current pulses for the negative current direction or other speed direction
have to be checked.
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