How To Find A Faulty Thyristor; Converters Size D1 To D4 (20; Blown Fuses - ABB DCS800 Service Manual

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A fuse has disconnected one of the six thyristors. This is possible only for
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converters with 900 ... 5200 A (six internal branch fuses). A converter with
three external fuses stops working completely at once when one of the three
AC input fuses interrupts a phase input of the converter.
A thyristor does not get firing pulses or does not react to firing pulses.
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The current controller may be totally mismatched to the DC load.
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The AC mains network is causing that fault message. In this case,
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asymmetrical phase shift, uneven phase voltage or critical designed power
factor correction equipment or harmonic reduction equipment can be the
reason.

How to find a faulty thyristor

If a blown fuse is suspected in the converter, the problem is caused most often by
a faulty thyristor. 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 instructions, related to the machine or the application itself,
are obeyed.
Converters size D1 to D4 (20...1000 A)
These converters require semiconductor fuses in the 3 AC lines.
The converter must be disconnected from the mains.
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One motor armature cable should be disconnected from the converter.
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Blown fuses

Using the OHM function of a normal multimeter, measurements must be made
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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 picture Anti-parallel B6-bridges with
branching fuses on page 45). Normally, every measurement should show high
resistance (> 1 k
Target: find a short circuit, indicated by low resistance ( <1
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thyristor).
If the converter is designed with half-bridge thyristor modules, then a module
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consists of two anti-parallel thyristors. In this case it is sufficient to know which
thyristor pair or module has a defective thyristor because the complete module
must be replaced.
After a thyristor module is replaced, the above mentioned measurement should
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be done another time to make sure that all faulty thyristors have been detected!
Note:
The RC circuit could also cause 0
The measurement, showing less resistance than 1
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.
).
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result for a short time.
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) (destroyed
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should be made a second
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