Blown Fuses; Faulty Thyristor - ABB DCT880 Service Manual

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Blown fuses

− Using the OHM function of a normal multimeter, measurements must be made from both sides of the
semiconductor fuses (e.g. U1 to thyristor, V1 to thyristor and W1 to thyristor):

Faulty thyristor

− Make sure, the internal fuses are fine.
− Using the OHM function of a normal multimeter, measurements must be made from both sides of the
thyristor power controller (e.g. U1 to U2, V1 to V2 and W1 to W2).
− Normally, each measurement should show high resistance (> 1 kΩ).
− Target: find a short circuit, indicated by low resistance (< 1 Ω) (destroyed thyristor).
− If the Thyristor power controller is designed with thyristor modules, then a module consists of two
thyristors. In this case, it is sufficient to know which thyristor module has a defective thyristor because the
complete module must be replaced.
− After a thyristor module is replaced, the above-mentioned measurement should be done another time to
make sure that all faulty thyristors have been detected!
Note:
The RC / snubber circuit could also cause 0 Ω result for a short time.
The measurement, showing less resistance than 1 Ω should be made a second time with test leads applied to
the terminals with opposite polarity; if this measurement shows the same result, one or two thyristors located
in that path are faulty; they need to be replaced.
Fault Tracing Thyristors
3ADW000449R0101 DCT880 Service Manual e a