Chapter 2 - Fault Tracing Thyristors
VI A
2 - 2
DCS 500 / DCS 600 Service Manual
How to find a faulty thy-
ristor
If a blown fuse is suspected in the converter, the problem is caused
most often by a faulty thyistor. To make sure, that a thyristor is the
reason and needs to be exchanged fault tracing must be done in
two different ways, depending on the size of the converter.
In general, make sure, that all safety instructions,
given within this manual or within the safety instruc-
tions, related to the machine or the application itself,
are obeyed.
Converters size C1
and C2/C2b
(25...1000 A)
These converters require semiconductor fuses in the 3 AC lines.
- The converter must be disconnected from the mains.
- One motor armature cable should be disconnected from the con-
verter.
Blown fuses
- 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; see
). Normally, every measurement should show high re-
sistance (> 1 k
Ω
). Target: find a short circuit, indicated by low re-
sistance ( <1
Ω
) (destroyed thyristor).
- If the converter is designed with half-bridge thyristor modules,
then a module consists of two antiparallel thyristors. In this case
it is sufficient to know which thyristor pair or module has a defec-
tive thyristor because the complete module must be replaced.
- After a thyristor module is replaced, the above mentioned meas-
urement should be done another time to make sure that all faulty
thyristors have been detected!
Note
The RC 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 the opposite polarity; if this
measurement shows the same result, one or two thy-
ristors located in that path are faulty; they need to be
replaced.
3ADW000093R0701_DCS500B/DCS600_Service manual_e_g
