Lightning Damage
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Below are some pictures
of parts of a Ziel Abegg lift motor drive (from a local hospital)
that suddenly blew up.
This specific drive weighs in
at 36.5Kgm (80pounds) and can drive a 37KW motor at 74A (or max
134A) |
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Most of these drives follow
a typical standard practice which is updated when new and hopefully
better components are made available. In this drive, a pretty
powerful example, individual motor power modules are used. Early
models would have used large "discrete" SCRs, triacs,
or more modern IGBTs with a rats nest of wiring, but integrated
modules offer reduced manufacturing costs. In smaller drives
U, V and W drive would be integrated into a single module. |
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On the right are "snubbers"
each using is a pair of resistors of 150 ohm, in parallel, with
a series 0.15uF capacitor (in red) across the three mains phases.
the resistors use 21SWG wire ends and each is fused open. The
fusing current of this wire is 58A so some 116A must have flowed
through the circuitry. Oddly each resistor still measures 150
ohms so the duration of the current must have been very short.
This is also the evidence from the red voltage surge protectors
which haven't disintegrated. |
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Below, a close up of the 3-phase
mains input tracking under the circuit protectors. What was the
purpose of the circuit protectors you might ask? Well, these
are in place to damp out only minor surges not a direct lightning
strike. |
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A few clues on the upper
surface but more evidence of what happened on the underside of
the second of the two pcbs which were mounted over the heatsink. |
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Below, the line-up of
motor drive modules (U, V and W) with that for the brake on the
right. |
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The bridge rectifier is
soldered in place unlike the plug-in motor modules. Picture taken
after cleaning away most of the soot. |
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A view of the rectifier which
might include a monitoring facility of the inputs. Unlike many failed rectifiers all the diodes
in the bridge are open circuit and in fact these parts rarely
fail.
I interpret this to have a rating
of 180A and 1600V |
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A view of one of three
of the three motor power modules on the left, and on the right
the brake module which is slightly different. Ratings appear
to be 220A and 1200V for the motor with 200A and 1200V for the
brake. |
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It remains to be seen
what damage there is to the other components (and of course track
ie. where did all that soot come from!) on the various circuit
boards.... |
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