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Converters size A5,
C3 and C4
(900...5150 A)
Blown fuses
Ripple monitor
DCS 500 / DCS 600 Service Manual
These converters are equipped with fuses in the branches of the
power part.
- The converter must be disconnected from the mains.
- 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
therefor the faulty branch is known (see Figure 4-4 ).
- The OHM test should be performed, when the thyristor is still
clamped. Outside the converter a special thyristor clamping de-
vice is needed.
- For 4-Q converters with antiparallel thyristors:
The selection of a forward or reverse thyristor is done during the
disassembly. Continue with related chapter 5, 6 or 7
Find faulty thyristor
- After a thyristor was replaced, the OHM test should be done an-
other time to make sure that all faulty thyristors have been de-
tected! If the motor is still connected to the converter the result of
the measurement may be wrong.
If the ripple monitor fault occured, the fault tracing must be adapted
to the reasons listed before:
- Check the fuses and the thyristors, according to the statements
before.
- If the power section seems to be ok, but still one or more thyris-
tors don´t take current, something went wrong in between the
firing pulse generation and the thyristor´s gate; in this case
check:
• Is a firing pulse present on the primary side of the firing pulse
transformer?
• Is a firing pulse present on the secondary side of the firing
pulse transformer?
• Is the firing pulse transfered to the gate of the thyristor? Are
there all electrical connections still healthy?
• Can the thyristor be fired with the applied firing pulse? Is the
pulse form of the firing pulse identical at all measuring posi-
tions?
- Check the settings of the current controller.
- Check the AC mains network by taking recordings of the line
voltage and current at all 3 phases at the same time.
3ADW000093R0601_DCS500B/DCS600_Service Manual_e_f
Chapter 2 - Fault Tracing Thyristors
VI A
2 - 3
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