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Fault Tracing Thyristors
3ADW000488R0101 DCS880 Service manual e a
Converters size H5 … H8 (900 ... 5200 A)
These converters are equipped with fuses in the branches of the power part.
− The converter must be disconnected from the mains.
Blown fuses
− Make sure, that the connection to the motor is open (e.g. disconnect motor cables).
− Using the OHM function of a normal multimeter, measurements must be made from each AC terminal to
each DC terminal (U1 to C1, V1 to C1, W1 to C1, U1 to D1, V1 to D1 and W1 to D1.
− In case of a blown fuse, the faulty thyristor or the faulty pair of thyristors are already isolated at one side
from the others and therefore the faulty branch is known:
Bridge configuration H5 … H8
− Normally, each measurement should show high resistance (> 1 kOhm).
− Target: Find a short circuit, indicated by low resistance (< 1 Ohm) (destroyed thyristor).
− Size H5 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. Continue with related part Exchange of Thyristors for Size H5
section Find faulty thyristor.
− For sizes H6 … H8 the OHM test should be performed, when the thyristor is still clamped. Outside the
converter a special thyristor clamping device is needed.
− For 4-Q converters with anti-parallel thyristors or BCT’s:
The selection of a forward or reverse thyristor or BCT (Bidirectional-Controlled-Thyristor) is done
during the disassembly.
Continue with related part Exchange of Thyristors for Size H6, H7 or H8
section Find faulty thyristor.
− After a thyristor was replaced, the OHM test should be done another time to make sure that all faulty
thyristors have been detected! If the motor is still connected to the converter the result of the measurement
may be wrong.
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